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Tomohito Yamada
Faculty of Engineering　Civil Engineering　Infrastructure and Management
Professor
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Last Updated :2024/05/09

Researcher Profile and Settings

Affiliation

  • Faculty of Engineering　Civil Engineering　Infrastructure and Management

Job Title

  • Professor

URL

Research funding number

  • 10554959

J-Global ID

Research Interests

  • 土壌水分   極端現象   全球気候モデル   陸面モデル   全球再解析データ   人工衛星   地球水循環   人間活動   準季節予報   大気陸面相互作用   予報スキル   予測可能性   水文気象   陸面状態   衛星植生観測情報   植生パラメータ   双方向ネスティング   海洋科学   モンスーン変動   陸面過程   自然現象観測・予測   海洋物理   計算物理   モンスーン   水工水理学   雲解像モデル   

Research Areas

  • Social infrastructure (civil Engineering, architecture, disaster prevention) / Hydroengineering

Educational Organization

Academic & Professional Experience

  • 2022/05 - Today Hokkaido University Professor
  • 2009/04 - 2022/04 Hokkaido University Associate Professor
  • 2007/04 - 2009/03 NASA Goddard Space Flight Center, Global Modeling and Assimilation Office / University of Maryland Baltimore County Research Associate

Research Activities

Published Papers

  • Yuta Ohya, Tomohito J. Yamada
    Journal of Hydroinformatics 1464-7141 2024/01/30 
    Abstract

    In recent years, line-shaped rainbands (LRBs) have increased in Hokkaido, Japan. LRBs caused several flood disasters historically, thus the meteorological patterns that cause them need to be investigated. This study aimed to understand statistically the relationship between LRBs and weather patterns during the summer months under climate change conditions. Our study investigates the link between LRBs and meteorological patterns in Hokkaido during July and August, using historical and climate prediction models. With a 2°/4° global temperature rise, LRB occurrences in this region increase by approximately 1.51/2.07 times. The highest occurrences of LRBs correlate with increased water vapor flux from the south and positive pressure anomalies over the Pacific Ocean. Three main meteorological patterns contribute significantly to LRBs: (1) a nearby low-pressure system, (2) a strengthening Pacific High frontal pattern, and (3) approaching or landing typhoons in Hokkaido. These patterns double the LRB occurrence probability, a trait observed across past and projected climates (+2K and +4K experiments). These are important insights for future flood risk management.
  • Kei KOURA, Naoki KOYAMA, Tadashi YAMADA, Tomohito J. YAMADA
    Japanese Journal of JSCE 80 (16) n/a - n/a 2024
  • Dan HASHIMOTO, Maki MIYAMOTO, Yuta OHYA, Tomohito J. YAMADA
    Japanese Journal of JSCE 80 (16) n/a - n/a 2024
  • Maki Miyamoto, Tomohito J. Yamada
    Hydrological Research Letters 18 (1) 28 - 34 2024
  • Tsuyoshi Hoshino, Tomohito J. Yamada
    Journal of Hydrology 617 128910 - 128910 0022-1694 2023/02
  • Maki MIYAMOTO, Tomohito J. YAMADA
    Japanese Journal of JSCE 79 (27) n/a - n/a 2023
  • Abhinav Dengri, Tomohito Yamada
    IOP Conference Series: Earth and Environmental Science 1136 (1) 012012 - 012012 1755-1307 2023/01/01 
    Abstract A simple soil-atmosphere interaction model is developed to study the bimodal distribution of soil moisture in regions where there is feedback between precipitation and soil moisture. Our study includes planetary boundary layer (PBL) feedback in the coupled analytical soil-atmosphere interaction model with a varying PBL height and entrainment from the free atmosphere. This study aims to reveal the dominant PBL feedbacks that impact the occurrence of soil moisture bimodality by comparing the evolution of prognostic variables for a detailed PBL scheme (with varying PBL height and entrainment of heat and moisture from the free atmosphere) with the simple PBL scheme (with fixed PBL height and no entrainment). This study has shown the existence of multiple equilibria in the continental water balance for both detailed PBL and simple PBL schemes when the model is integrated for different initial soil moisture up to equilibria. Although both with and without PBL feedback, the results are in qualitative agreement; the soil moisture initialization to realize multiple equilibria of a detailed PBL scheme is larger than the simple PBL scheme. Although the direct quantitative comparison with observation is clearly limited in the simple model, it also demonstrates how the non-linear dynamics of the coupled soil-atmosphere system may be expected to occur in observations.
  • Kotaro Miyazaki, Tsuyoshi Hoshino, Keita Shimizu, Sourabh Shrivastava, Tomohito J Yamada
    IOP Conference Series: Earth and Environmental Science 1136 (1) 012027 - 012027 1755-1307 2023/01/01 
    Abstract The Hokkaido Eastern Iburi earthquake in 2018 induced the largest landslide over the Azuma River basin in Hokkaido, the north island of Japan. This study estimated the sediment erosion rate over the Azuma River basin using the universal soil loss equation (USLE) for the pre- and post-earthquake conditions. The results showed that the potential sediment erosion rate from the entire basin increased by 8–29 times more than the pre-earthquake condition. The primary cause of the increase in sediment erosion rate was deforestation due to the landslide, which generated 13% of the bare land area in the entire basin. In addition, the influence of interannual variability of rainfall on sediment erosion rate was calculated from observed rainfall data. As a result, the minimum annual sediment erosion rate after the earthquake exceeded the maximum before the earthquake, indicating that the post-earthquake sediment erosion rate is substantially higher than the pre-earthquake rate. These findings suggest that in order to assess the sediment erosion risk over the Azuma River basin, it is necessary to predict and monitor the vegetation recovery, considering the interannual variability of rainfall.
  • Yuta Ohya, Tomohito J Yamada
    IOP Conference Series: Earth and Environmental Science 1136 (1) 012025 - 012025 1755-1307 2023/01/01 
    Abstract Line-shaped rainbands (LRBs), including Mesoscale Convective Systems (MCSs), stagnate on river basins and cause floods and landslides. Moreover, the frequency of LRBs is increasing around Hokkaido a part of northern Japan. Due to the complexity of the three-dimensional structures found in LRBs, some research dealt with two-dimensional observation data to identify them for the sake of simplicity. In previous studies, several methods to widely identify LRBs from radar rainfall data in terms of rainfall intensity, shape of rainfall area, and duration have been proposed. However, using the nationally consistent definition, the number of LRBs occurring in this region would be evaluated as very few due to the little rainfall climatology of this area. In this study, based on the previous studies, we adjust many combinations of threshold values, such as rainfall intensity, aspect ratio, and time duration in order to verify of validity the LRBs that occurred in northern Japan. The authors visually identified the six LRBs that caused the disaster and showed thresholds at which they were mechanically extractable by a computer program. The combination of thresholds that included at least six of those disaster-scale cases was “a rainfall area defined by a closed curve with a previous 3-hour rainfall of 40 mm or more, stagnating for 2 hours or more (covering 40% or more of its area), and with a maximum aspect ratio of 2.5 or more.”
  • Maki Miyamoto, Tomohito J. Yamada
    IOP Conference Series: Earth and Environmental Science 1136 (1) 012023 - 012023 1755-1307 2023/01/01 
    Abstract Atmospheric fronts play an important role on the day-to-day variation of rainfall in Japan, North-western Pacific. They are defined as a discrepancy of air density and have been depicted on surface weather charts for more than 100 years by Japan Meteorological Agency (JMA). This study develops an approach to detect fronts from the charts published from 1978 to 2020 and investigates how detected fronts could be utilized. The fronts which are depicted on the charts might have a diverse physical characteristic in each age. One of factors is a difference in how to represent fronts. The difference also prevents from detecting fronts under a certain accuracy. Previous study demonstrates detecting fronts based on the color available from the charts. However, this approach is applicable for weather charts published after 2000 by JMA. This paper describes consideration points for a unified detection of fronts from the charts for 43 years in detail. Furthermore, we compare fronts detected by several methods and discuss a spatial scale in which their differences could be neglected.
  • Sho Kawazoe, Masaru Inatsu, Tomohito J. Yamada, Tsuyoshi Hoshino
    Journal of Applied Meteorology and Climatology 1558-8424 2022/12/22 
    Abstract This study investigates the impact of future climate warming on tropical (TC) and extratropical cyclones (ETC) using the database for Policy Decision-making for Future climate change (d4PDF) large ensemble simulations. Cyclone tracking was performed using the Neighbor Enclosed Area Tracking algorithm (NEAT), and TC and ETCs were identified over the western North Pacific (WNP). For cyclone frequency, it was revealed that while a slight underestimation of the total number of TCs and ETCs in both the WNP and near Hokkaido, Japan, exists, the d4PDF reproduced the spatial distribution of both TC and ETC tracks well compared to observations/reanalysis. The 4-K warming scenarios derived from six different sea surface temperature warming patterns showed robust decreases in TC frequency in the tropical WNP and a slight reduction in ETCs near Japan. Next, precipitation characteristics for TCs or ETCs in the vicinity of Hokkaido were examined using 5 km-mesh regional climate ensemble simulations. Four representative cyclone locations near Hokkaido are identified using K-means clustering and revealed distinct precipitation characteristics between clusters, with higher TC-associated precipitation than ETC-associated precipitation and the heaviest precipitation in the southern portion of the prefecture. The 4-K warming scenarios revealed increased precipitation for all cyclone placements for both TCs and ETCs. Lastly, average cyclone intensity, translation speed, and size were examined. It was shown that TCs in future climates are more intense, propagate more slowly, and are smaller in terms of enclosed vorticity area as they approach Hokkaido. For ETCs, mean intensity does not change much, they travel slightly faster, and become smaller.
  • Tomohito J. Yamada, Sourabh Shrivastava, Ryosuke Kato
    Theoretical and Applied Climatology 150 (1-2) 73 - 83 0177-798X 2022/10 [Refereed]
     
    Abstract Earlier onset of the Southeast Asian summer monsoon (SAM) was observed over the Chao Phraya River basin in Thailand using Thai Meteorological Department-derived high-resolution merged rainfall data from 1981 to 2016. SAM variability depends on numerous local and global factors, including thermal conditions over the Bay of Bengal (BoB) and Tibetan Plateau (TbT). Despite tremendous past research efforts, the effect of thermal heat contrast on the SAM remains unclear. Using observational and reanalysis datasets, we found that the absolute value of total heat over the BoB was increasing. However, the interannual variability of total heat was greater over the TbT. Changes in surface temperature (± 1.5 °C), air thickness (± 20 m), and geopotential height over the TbT were associated with the timing of SAM onset. The results also suggested that significant changes in air thickness are driven by surface temperature differences over the TbT, while changes in the integrated apparent heat source and integrated apparent moisture sink of ± 100 W m−2 resulted in anomalous convective activities over the BoB and mainland of the Indochina Peninsula in years of early and late SAM onset. At the intraseasonal timescale, Madden–Julian oscillation (MJO) was observed over the Indian Ocean and Western Hemisphere for 4–10 days in years of early SAM onset. The opposite situation was found for years of late SAM onset, with MJO located over the Western Pacific Ocean and Maritime Continent.
  • Shaik Allabakash, Sanghun Lim, Kyu-Soo Chong, Tomohito J. Yamada
    Remote Sensing 14 (19) 4849 - 4849 2022/09/28 [Refereed]
     
    Air pollution is a serious challenge in South Korea and worldwide, and negatively impacts human health and mortality rates. To assess air quality and the spatiotemporal characteristics of atmospheric particulate matter (PM), PM concentrations were compared with meteorological conditions and the concentrations of other airborne pollutants over South Korea from 2015 to 2020, using different linear and non-linear models such as linear regression, generalized additive, and multivariable linear regression models. The results showed that meteorological conditions played a significant role in the formation, transportation, and deposition of air pollutants. PM2.5 levels peaked in January, while PM10 levels peaked in April. Both were at their lowest levels in July. Further, PM2.5 was the highest during winter, followed by spring, autumn, and summer, whereas PM10 was the highest in spring followed by winter, autumn, and summer. PM concentrations were negatively correlated with temperature, relative humidity, and precipitation. Wind speed had an inverse relationship with air quality; zonal and vertical wind components were positively and negatively correlated with PM, respectively. Furthermore, CO, black carbon, SO2, and SO4 had a positive relationship with PM. The impact of transboundary air pollution on PM concentration in South Korea was also elucidated using air mass trajectories.
  • Takeshi KODAMA, Keita SHIMIZU, Tomohito J, YAMADA
    河川技術論文集 28 343 - 348 2022/06 [Refereed]
  • 日蘭共同研究「Flood Risk and Climate Change Hokkaido （北海道における氾濫リスクと気候変動）」最終報告書
    Bob Maaskant, Bas Kolen, Mark Hegnauer, 千葉学, 植村郁彦, 山田朋人
    2022/02
  • Yuta OHYA, Maki MIYAMOTO, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 78 (2) I_43 - I_48 2022
  • Yuka Kanamori, Masaru Inatsu, Ryoichi Tsurumaki, Naoki Matsuoka, Tsuyoshi Hoshino, Tomohito J. Yamada
    SOLA 18 249 - 253 2022
  • OHYA Yuta, YAMADA Tomohito J.
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 公益社団法人 土木学会 78 (5) I_225 - I_231 2022 
    Using observations and the Ensemble Climate Prediction Database (d4PDF), we analyzed the occurrence characteristics of linear and stagnant precipitation bands. In recent years, heavy rainfall disasters involving LRB have been frequent all over Japan, and the Japan Meteorological Agency defines a linear precipitation bands from the shape and stagnation time of precipitation zones of 80 mm/3h or more from the aspect of disaster prevention. In Hokkaido, however, several floods and landslides have occurred even with much lower precipitation than that. In this study, LRB are redefined for the Hokkaido region, and the frequency of occurrence, regional distribution, and model characteristics in past and present climates are shown through observations and application to the d4PDF.
  • MIYAMOTO Maki, YAMADA Tomohito J.
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 公益社団法人 土木学会 78 (5) I_151 - I_156 2022 
    In this study, a method for extracting fronts from weather maps treated as weather information was developed and applied to 34 years of weather maps. The front can now be treated as grid data, and it is shown that rainfall within 100 km around the front accounts for more than 30% of the rainfall in the Kyushu region in June and July. Furthermore, it was found that the spatial mean rainfall over the area passed by the front as it moved meridionally over the Kyushu region reached a maximum when the front moved about 300 kilometers. The weather patterns suggest that the north-south movement of the front is affected by moving depression with fronts, the approach of a typhoon or tropical cyclone, and an enhancement of an anticyclone.
  • OKACHI Hiroki, YAMADA Tomohito J.
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 公益社団法人 土木学会 78 (5) I_171 - I_177 2022 
    Drop size distribution of sea spray generated from wave breakings can be a confounding factor for rainfall observations at sea, and has significance as a sea-salt particle that causes salt damage and rainfall inland. In this study, field observations of sea spray were conducted using a disdrometer, and drop size distribution equation as a function of wind speed was proposed. The proposed equation enables the estimation of the amount of sea spray that can be mixed during rainfall observations and the estimation of the amount of sea spray that are the source of sea salt particles that cause salt damage and cause rainfall.
  • Dengri Abhinav, Yamada Tomohito
    水文・水資源学会研究発表会要旨集 水文・水資源学会 35 257  2022 
    We study bimodal distribution for soil moisture and precipitation using satellite dataset over the northern Indian region. Strong soil moisture bimodality is present over northern india which is caused by clear transition from dry to wet season.
  • 高薮 出, 辻野 博之, 村田 昭彦, 川瀬 宏明, 仲江川 敏之, 山田 朋人, 山崎 剛, 石川 洋一, 坪木 和久
    水文・水資源学会研究発表会要旨集 水文・水資源学会 35 113  2022 
    将来の水文・水資源の様相を評価するためには、将来気候変動の予測が必要不可欠である。気候変動予測シミュレーション技術の高度化等による将来予測の不確実性の低減や、気候変動メカニズムの解明に関する研究開発、気候予測データの高精度化等からその利活用までを想定した研究開発を一体的に推進することで、気候変動対策に活用される科学的根拠を創出・提供することを目的とした、文部科学省「気候変動予測先端研究プログラム」が開始された。このプログラムの下、日本域における気候変動予測の高度化を目指して（領域課題３：「日本域における気候変動の高度化」）、1：日本域気候変動の予測システム開発とメカニズム解明、2：極端現象のメカニズム解明による地域・流域に応じた適応策推進に資する気候変動予測情報の創出、3：海外の脆弱地域における高精度気候予測データセットの創出に、我々は取り組んでいる。また、水文・水資源分野を始めとして、多様なユーザーとの対話を通して、気候変動予測の共通認識の醸成を目指している。これらの研究目標の基盤となる研究を、すでに文部科学省「統合的気候モデル高度化研究プログラム」等で実施してきた。その成果の一例として、大気海洋相互作用を表現可能な日本域気候変動予測システム(Time Sequential Experiments with Coupled model; TSE-C）の開発や、近年洪水事例が多発している要因がこれまでの温暖化によるのか、それ以外の要因かを明らかにするイベントアトリビューション研究が挙げられる。気候変動予測の現在地点と今後の計画を紹介し、議論の端緒としたい。
  • 石原 道秀, 山田 朋人
    水文・水資源学会研究発表会要旨集 水文・水資源学会 35 285  2022 
    気候変動の影響により水害の更なる頻発・激甚化が懸念される中，流域治水関連法が令和3年11月に施行された．流域治水のおける治水計画では，流域を集水域・河川区域・氾濫域の3つから捉え，1)氾濫をできるだけ防ぐ・減らす対策，2)被害対象を減少させるための対策，3)被害の軽減，早期復旧・復興のための対策，をハード・ソフト一体で多層的に進められている1)．これらの対策の具体のうち，本研究と関連するものは遊水池整備である． 遊水池は，洪水を一時的に貯めることで下流に洪水が一気に流れ出すことを防ぐ役割を持つ．遊水池が効果を発揮した一例として，釧路川および釧路湿原における2016年8月の大雨に伴う出水がある．釧路川および釧路湿原では，湿原が持つ遊水機能を高めるために，湿原の下流端に横堤が設置されている．これにより2016年8月の大雨では，湿原に約2.1千万m3の水量（東京ドーム約17杯分）を貯留し，横堤下流側の水位が低減したことが試算されている2)．将来予測の不確実性を考慮した上で流域治水を実施するには，外力規模ごとの遊水池の効果の定量化が必要となるはずである．そこで本研究では，ある外力に対する横堤の規模の違いから遊水機能がどう変化するのか把握することを目的に，釧路川および釧路湿原を模した簡易的な数値実験による感度分析を実施した．
  • 内藤 大梧, 山田 朋人
    水文・水資源学会研究発表会要旨集 水文・水資源学会 35 245  2022 
    泥炭地は地域特有の植生と高い地下水位によって成立しており，急速な温暖化の進行や人為的な地域水文環境の変動によって大きな影響を受ける可能性がある．一方で泥炭地の経年変化を数理モデル化した「泥炭堆積モデル(Peat Accumulation model）」においてその目的の多くは気候変動に対する炭素の固定量の変化の算出であり，透水係数をはじめとする各係数や堆積量などについて実際の泥炭地での観測との比較が行われた例は少ない．そのため，泥炭堆積モデルにおいて計算された各係数の値が，実際の値と一致しない可能性がある． ここでは，泥炭堆積モデルの最新モデルの一つであるMPeatについて感度分析を行い，どのようなパラメータがモデルの計算結果により大きな影響を及ぼすのか，観測結果と照らし合わせる必要があるかを明らかにした． 泥炭堆積モデルMPeatの感度分析の結果，泥炭地の半径や透水係数のパラメータ，ヤング率のパラメータ，植物の生産量がモデルの結果に特に大きな影響を与えていることが確認された．泥炭堆積モデルによる堆積予測を行う際には，対象地域の泥炭の特性を観測などにより十分理解する必要があると思われる．
  • 宮本 真希, 山田 朋人
    水文・水資源学会研究発表会要旨集 水文・水資源学会 35 249  2022 
    日本が位置する中緯度帯において，年間降水量のうち約7割は前線による降水である．前線に伴う豪雨災害は広範囲かつ甚大であり，例えば令和2年7月豪雨や平成30年7月豪雨では西日本を中心に，昭和56年水害では北海道の道央において被害が拡大した．これらは各地域の代表的な豪雨災害であるため，日本全国を対象として，前線に伴い生じる豪雨を議論する必要がある．天気図に示された前線はUtsumi et al. (2014)が提案した手法により1度格子データとして利用可能である．本研究では，より空間解像度の高いグリッドデータを作成し，前線データの活用について議論する． 対象期間は1978年から2020年の6月から10月とした．既往手法に加えて，本研究では，高解像度グリッドデータを作成するために物体認識および形状認識により三角および半円を取り除き，線として前線を表した．さらに，1999年以前の天気図においては前線が黒で描かれており，そのままでは色に基づく前線抽出が行えないため，目視による判断で前線を色付けして43年間の前線データを作成した． 作成した前線データは，前線の幅は約100kmであると仮定した場合，どの抽出方法においても概ね同質である．空間解像度を0.1度した場合においても抽出方法による前線の位置の違いは数十kmにとどまるため，天気図スケールより小さい空間スケールに対しても有用であると推測される．
  • 青木 一眞, 山田 朋人
    水文・水資源学会研究発表会要旨集 水文・水資源学会 35 197  2022 
    湖の水温は水面の熱収支の問題であり、季節や、それぞれのダム湖が位置する気候によって湖中の水温構造は変化する。水温構造の変化や、それに伴う水質の変化は、湖の生態系や、農業、工業、生活用水などの利水に影響を及ぼす。本研究では全国の湖やダム湖における水温構造、水質変化、全層循環の発生の有無の詳細な検討や、それらの将来における変化を示すことを目標とし、本稿ではその第一段階として十勝ダムにおける東大雪湖について鉛直1次元の水温解析モデルを適用した結果を示す。
  • 岡地 寛季, 山田 朋人
    水文・水資源学会研究発表会要旨集 水文・水資源学会 35 43  2022 
    海面抵抗の大きさの指標となる海面抵抗係数は従来風速に対して単調増加として扱われるが，Powell et al. (2003)は暴風時に減少することを観測より示した．近年はある風速を超えると一定値となることが示唆されている．しかし，海面近傍の飛沫の質量密度や水平風速は暴風雨下かつ混相流としての基礎的な物理量であるが，極端現象が生起することが稀有であることや暴風雨下での観測が困難であるという背景を有する．そこで本研究は極端現象下の海面近傍の領域を対象にレーダ観測を実施し，飛沫の質量密度及び水平風速の推定手法を提案する．
  • 大屋 祐太, 山田 朋人
    水文・水資源学会研究発表会要旨集 水文・水資源学会 35 253  2022 
    本研究は，北海道とその周辺域の観測データおよび大量アンサンブルデータから同地域における降雨量が集中する7-9月に発生した線状かつ停滞性を有する豪雨を客観的に抽出した．特に同地域は日本海・太平洋・オホーツク海の特性の異なる海に囲われ，大雪山系・日高山脈の地形によるエリアごとの気候特性を有するため，こうした特徴に注目し，議論を行う．
  • 気候変動を考慮した流域全体を俯瞰した水害リスクの考え方
    山田朋人
    日本不動産学会誌 36 (1(140)) 2022 [Not refereed]
  • 日蘭共同研究「Flood Risk and Climate Change Hokkaido （北海道における氾濫リスクと気候変動）」詳細報告書１
    星野剛, Mark, H, 清水啓太, 山田朋人
    2022
  • Tesfa Gebrie Andualem, Mulatu Kassa, Girum Getachew Demeke, Guna Hewa, Imran Ahmed Dar, Quoc Bao Pham, Tomohito J. Yamada
    Sustainable Water Resources Management 7 (6) 2363-5037 2021/12 [Refereed]
  • Yulong Zhu, Tatsuya Ishikawa, Tomohito J. Yamada, Srikrishnan Siva Subramanian
    Journal of Infrastructure Preservation and Resilience 2 (1) 2021/12 [Refereed]
     
    AbstractTo semi-quantitatively assess the effects of climate change on the slope failures, this paper proposes an effective approach for evaluating the influences of climate change on slope stability in seasonally cold regions. To discuss climate change, this study firstly analyzes the trend of the two main climate factors (precipitation and air temperature) based on the regression analysis results of the meteorological monitoring data during the past 120 years in different scales (e.g., world, country (Japan), and city (Sapporo)), and the downscaled outputs of three different regional atmospheric models (RAMs) with lateral boundary conditions from three different general circulation models (GCMs). Next, to discuss the effects of different climate factors (air temperature, precipitation, etc.) and to determine the key climate factors on the slope instability, a slope stability assessment approach for evaluating the effects of climate changes on slope instability is proposed through the water content simulation and slope stability analysis with considering freeze-thaw action. Finally, to check the effectiveness of the above assessment approach, assessment of instability of an actual highway embankment slope with the local layer geometry is done by applying the past and predicted future climate data. The results indicate that affected by global warming, the air temperature rise in some cold cities is more serious. The climate changes (especially the increase in precipitation) in the future will increase the infiltration during the Spring season. It will lengthen the time that the highway slope is in an unstable state due to high volumetric water content, causing the occurrence of slope failures will be more concentrated in April. While during the Ssummer-Autumn period, the time domain of its occurrence will become wider.
  • Construction of a High-resolution Ensemble Climate Dataset for Duture Projection of Flood Risk in the Kanto Region
    山田朋人, 星野剛, 清水啓太, 成岱蔚
    Annual Report of the Earth Simulator April 2020 - February 2021 2021/10
  • Assessment of Future Flood Risks and Its Cause using Dynamical Downscaling
    星野剛, 山田朋人
    Annual Report of the Earth Simulator April 2020 - February 2021 2021/10
  • Tomohito J. Yamada, Tsuyoshi Hoshino, Akihiro Suzuki
    Atmospheric Science Letters 22 (8) 1530-261X 2021/08/04 [Refereed]
  • Thanh Thu Nguyen, Makoto Nakatsugawa, Tomohito J. Yamada, Tsuyoshi Hoshino
    Water 13 (7) 896 - 896 2021/03/25 [Refereed]
     
    This study aims to evaluate the change in flood inundation in the Chitose River basin (CRB), a tributary of the Ishikari River, considering the extreme rainfall impacts and topographic vulnerability. The changing impacts were assessed using a large-ensemble rainfall dataset with a high resolution of 5 km (d4PDF) as input data for the rainfall–runoff–inundation (RRI) model. Additionally, the prediction of time differences between the peak discharge in the Chitose River and peak water levels at the confluence point intersecting the Ishikari River were improved compared to the previous study. Results indicate that due to climatic changes, extreme river floods are expected to increase by 21–24% in the Ishikari River basin (IRB), while flood inundation is expected to be severe and higher in the CRB, with increases of 24.5, 46.5, and 13.8% for the inundation area, inundation volume, and peak inundation depth, respectively. Flood inundation is likely to occur in the CRB downstream area with a frequency of 90–100%. Additionally, the inundation duration is expected to increase by 5–10 h here. Moreover, the short time difference (0–10 h) is predicted to increase significantly in the CRB. This study provides useful information for policymakers to mitigate flood damage in vulnerable areas.
  • Masashi Kiguchi, Kumiko Takata, Naota Hanasaki, Boonlert Archevarahuprok, Adisorn Champathong, Eiji Ikoma, Chaiporn Jaikaeo, Sudsaisin Kaewrueng, Shinjiro Kanae, So Kazama, Koichiro Kuraji, Kyoko Matsumoto, Shinichiro Nakamura, Dzung Nguyen-Le, Keigo Noda, Napaporn Piamsa-Nga, Mongkol Raksapatcharawong, Prem Rangsiwanichpong, Sompratana Ritphring, Hiroaki Shirakawa, Chatuphorn Somphong, Mallika Srisutham, Desell Suanburi, Weerakaset Suanpaga, Taichi Tebakari, Yongyut Trisurat, Keiko Udo, Sanit Wongsa, Tomohito Yamada, Koshi Yoshida, Thanya Kiatiwat, Taikan Oki
    Environmental Research Letters 16 (2) 023004 - 023004 1748-9326 2021/02/01 [Refereed]
     
    Thailand plays a central economic and policy-making role in Southeast Asia. Although climate change adaptation is being mainstreamed in Thailand, a well-organized overview of the impacts of climate change and potential adaptation measures has been unavailable to date. Here we present a comprehensive review of climate-change impact studies that focused on the Thai water sector, based on a literature review of six sub-sectors: riverine hydrology, sediment erosion, coastal erosion, forest hydrology, agricultural hydrology, and urban hydrology. Our review examined the long-term availability of observational data, historical changes, projected changes in key variables, and the availability of economic assessments and their implications for adaptation actions. Although some basic hydrometeorological variables have been well monitored, specific historical changes due to climate change have seldom been detected. Furthermore, although numerous future projections have been proposed, the likely changes due to climate change remain unclear due to a general lack of systematic multi-model and multi-scenario assessments and limited spatiotemporal coverage of the study area. Several gaps in the research were identified, and ten research recommendations are presented. While the information contained herein contributes to state-of-the-art knowledge on the impact of climate change on the water sector in Thailand, it will also benefit other countries on the Indochina Peninsula with a similar climate.
  • Maki MIYAMOTO, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 77 (2) I_463 - I_468 2021
  • 内外水同時解析による浸水発生要因に着目した浸水被害特性の評価手法の提案
    米田駿星, 佐藤誠, 川村育男, 山田朋人
    河川技術論文集 27 517 - 522 2021 [Refereed]
  • 流域治水の検討に資するオランダの遊水地化事業に関する調査報告
    戸村翔, 千葉学, 山本太郎, 武田淳史, 植村郁彦, 舛屋繁和, 大村宣明, 吉田隆年, 星野剛, 山田朋人, 中津川誠
    河川技術論文集 27 591 - 596 2021 [Refereed]
  • d4PDFを活用した発電専用ダムによる洪水被害軽減運用手法の効果検証
    松本知士, 池田典之, 河田暢亮, 山田朋人, 中津川誠, 中北英一
    河川技術論文集 27 637 - 642 2021 [Refereed]
  • 風速シア無し・安定度一定条件のおろし風の水理学的表現の検討
    北野慈和, 山田朋人
    土木学会論文集B1(水工学) 77 1315 - 1320 2021 [Refereed]
  • アンサンブル気候データを用いた降雨強度-気温の関係の分析
    星野剛, 山田朋人
    土木学会論文集B1(水工学) 77 1267 - 1272 2021 [Refereed]
  • Analytical Land-vegetation-atmosphere Model to Study Soil Moisture Bimodality
    A. Dengri, T. J. Yamada
    Journal of Japan Society of Civil Engineers, Ser. B1(Hydraulic Engineering) 77 235 - 240 2021 [Refereed]
  • 九州地方を対象とした梅雨期における前線および周辺環境場の年々特性
    宮本真希, 山田 朋人
    土木学会論文集B1(水工学) 77 463 - 468 2021 [Refereed]
  • 情報理論を導入した確率降雨量の統合的将来予測
    清水啓太, 山田朋人
    土木学会論文集B1(水工学) 77 163 - 168 2021 [Refereed]
  • 現代ポートフォリオ理論を用いた降雨時空間分布の不確実性を考慮した流域内各河川への効率的な投資比率について
    舛屋繁和, 千葉 学, 山田 朋人
    土木学会論文集B1(水工学) 77 1399 - 1404 2021 [Refereed]
  • Hayase YONEDA, Ikuo KAWAMURA, Shigeo OKAWA, Makoto SATO, Tomohito YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 77 (2) I_1285 - I_1290 2021 [Refereed]
  • Daiwei Cheng, Keita Shimizu, Tomohito J. Yamada
    Hydrological Research Letters 15 (4) 84 - 91 2021 [Refereed]
  • Hiroki Okachi, Tomohito J. Yamada, Yasuyuki Baba, Teruhiro Kubo
    Atmosphere 11 (11) 1210 - 1210 2020/11/09 [Refereed]
     
    The effects of sea spray on open-ocean rainfall measurements-the drop size distribution (DSD) and rainfall intensities-were studied using a state-of-the-art optical disdrometer. The number of rain droplets less than 1 mm in diameter is affected by several factors, including the type of rainfall and seasonality. Over the ocean, small rain and large sea spray droplets co-exist in the same diameter size class (0.072 to 1000 mm); hence, sea spray creates uncertainty when seeking to characterize the drop size distribution (DSD) of rain droplets over the ocean. We measured droplet sizes at a marine tower using a state-of-the-art optical disdrometer, a tipping-bucket rain gauge, a wind anemometer, and a time-lapse camera, over a period that included typhoon Krosa of 2019. The number of rain droplets of diameter less than 1 mm increased monotonically as the horizontal wind speed became stronger. Thus, the shape parameter μ of the Ulbrich distribution decreased. This decreasing trend can be recognized as an increase in sea spray. During no-rainfall hours (indicated by rain gauges on the ocean tower and nearby land), sea spray DSDs were obtained at various horizontal wind speeds. Furthermore, the proportions of sea spray to rainfall at different rainfall intensities and horizontal wind speeds were determined; at a horizontal wind speed of 16 to 20 m s−1, the average sea spray proportions were 82.7%, 19.1%, and 5.3% during total rainfall periods of 2.1 mm h−1, 8.9 mm h−1, and 32.1 mm h−1, respectively. Representation of sea spray DSDs, as well as rainfall DSDs, is a key element of calculating real rainfall intensities over the open ocean.
  • Keita Shimizu, Tadashi Yamada, Tomohito J. Yamada
    Water 12 (10) 2727 - 2727 2020/09/29 [Refereed]
     
    Nonstationarity in hydrological variables has been identified throughout Japan in recent years. As a result, the reliability of designs derived from using method based on the assumption of stationary might deteriorate. Non-stationary hydrological frequency analysis is among the measures to counter this possibility. Using this method, time variations in the probable hydrological quantity can be estimated using a non-stationary extreme value distribution model with time as an explanatory variable. In this study, we build a new method for constructing the confidence interval regarding the non-stationary extreme value distribution by applying a theory of probability limit method test. Furthermore, by introducing a confidence interval based on probability limit method test into the non-stationary hydrological frequency analysis, uncertainty in design rainfall because of lack of observation information was quantified, and it is shown that assessment pertaining to both the occurrence risk of extremely heavy rainfall and changes in the trend of extreme rainfall accompanied with climate change is possible.
  • Keita Shimizu, Tadashi Yamada, Tomohito J. Yamada
    Water 12 (9) 2554 - 2554 2020/09/12 [Refereed]
     
    The shortage of extreme rainfall data gives substantial uncertainty to design rainfalls and causes predictions for torrential rainfall to deviate strongly from adopted probability distributions used in river planning. These torrential rainfalls are treated as outliers which existing studies do not evaluate. However, probability limit method test which its acceptance region expresses with high accuracy the range where observed ith order statistics could realize. Confidence interval which quantifies uncertainty of adopted distributions can be constructed by assuming that these critical values in both sides of the adopted region follow the same function form applied to actual observed data. Furthermore, its validity is proved through comparison of confidence interval derived from ensemble downscaling calculations. In addition, these critical values are almost in accordance with outliers in samples from the ensemble downscaling calculations. Therefore, prediction interval which expresses the range that an unknown observed datum can take is constructed by extrapolating the critical values for limit estimation of a future datum. In this paper, quantification method of uncertainty of design rainfall and occurrence risk of outliers in the traditional framework, using the proposed confidence interval and prediction interval, is shown. Moreover, their application to future climate by using Bayesian statistics is explained.
  • Tsuyoshi Hoshino, Tomohito J. Yamada, Hiroaki Kawase
    Atmosphere 11 (5) 435 - 435 2020/04/25 [Refereed]
     
    Previous studies have shown that the acceleration of global warming will increase the intensity of rainfall induced by tropical cyclones (TCs) (hereinafter referred to as “TC-induced rainfall”). TC-induced rainfall is affected by TC position and topography (slope shape and direction). Thus, TC-induced rainfall is expected to vary by sub-basin due to varying topographies. However, these relationships have not been explained, as historical TCs, which occurred several decades earlier, do not exhaustively encompass all TC positions that could potentially affect each basin. We used large ensemble regional climate model experiments with 5 km grid spacing, which enabled us to prepare a huge TC database for understanding the characteristics of TC-induced rainfall over sub-basins. We quantified the characteristics of TC-induced rainfall (rainfall volume, relationship between TC position and rainfall intensity, and contribution of TC intensity on rainfall) over four sub-basins in the Tokachi River basin, central Hokkaido, northern Japan. The results reveal differences in TC-induced rainfall characteristics between the sub-basins. In addition, the large ensemble data under a future climate scenario were used to evaluate future changes in the characteristics of TC-induced rainfall for each sub-basin.
  • Tomohito J. Yamada, Chhay Ngorn Seang, Tsuyoshi Hoshino
    Atmosphere 11 (4) 371 - 371 2020/04/10 [Refereed]
     
    Record-breaking precipitation events have been frequent in Japan in recent years. To investigate the statistical characteristics of the frequency of record-breaking events, observations can be compared with the values derived from sampling theory with a stationary state. This study counted the number of record-breaking daily and 3-day total precipitation events at 58 rain-gauge stations in Japan between 1901 and 2018. The average number of record-breaking events over the 118-year period was 5.9 for daily total precipitation, which is larger than the theoretical value of 5.4 derived using the assumption that the climate system over the same period was stationary. Sampling theory was used to incorporate the influence of the long-term temperature trend from the Clausius–Clapeyron relation associated with the saturation vapor pressure. In theory, the long-term temperature trend gives a similar number of observed record-breaking events when the long-term temperature trend is approximately 0.5 Kelvin/100 years.
  • Yuta OHYA, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 76 (2) I_193 - I_198 2020
  • Yasuyuki Baba, Teruhiro Kubo, Nobuhito Mori, Yasunori Watanabe, Tomohito Yamada, Ayumi Saruwatari, Junichi Otsuka, Yusuke Uchiyama, Junichi Ninomiya, Tomoya Shimura
    22nd Congress of the International Association for Hydro-Environment Engineering and Research-Asia Pacific Division, IAHR-APD 2020: "Creating Resilience to Water-Related Challenges" 2020 
    This paper shows some observation results on high wave condition due to typhoons measured at an offshore observation tower. Japan is affected by typhoons every year, and some typhoons cause serious damages in Kii peninsula and its surrounding areas sometimes. In 2018, three typhoons (No.20, 21, 24) approached around the Kii peninsula, and the severe wave conditions caused by the typhoon Jebi (No.21) and the typhoon Trami (No.24) are observed at the observation tower of SOO. During the typhoon Jebi and the typhoon Trami approaching, the maximum significant wave heights reach 9.60m by the typhoon Jebi and 11.09m by the typhoon Trami, respectively. On the other hand, wave condition caused by the typhoon Cimaron (No.20) is relatively milder than the ones by the typhoon Jebi and the typhoon Trami, even though a central atmospheric pressure and the distance between the center of the typhoon and the observation tower are similar to those of the typhoon Jebi and the typhoon Trami. In case of 2018, it is pointed out that the magnitude of high wave condition is associated with the offshore wave direction around Kii peninsula because the observation site opens to the south-west (between about 190deg and 240deg). In this paper, the factors and backgrounds related to high wave conditions by typhoons are discussed based on the observation results including other typhoon cases.
  • 2014年9月に発生した線状降水帯における鉛直渦構造と降水強度の関係
    大屋祐太, 山田朋人
    土木学会論文集B1(水工学) 76 193 - 198 2020 [Refereed]
  • 船舶レーダによる 2018 年夏季の観測と 散乱理論に基づく粒径分布のパラメタ推定手法
    岡地寛季, 山田朋人
    土木学会論文集B1(水工学) 76 181 - 186 2020 [Refereed]
  • FACTOR ANALYSIS FOR SPATIAL DEVIATION OF HEAVY RAINFALL IN TERMS OF DYNAMIC AND THERMODYNAMIC EFFECT
    星野剛, 山田朋人
    土木学会論文集B1(水工学) 76 19 - 24 2020 [Refereed]
  • 気候変動予測情報を用いた極値水文量の統計的推定
    清水啓太, 山田正, 山田朋人
    河川技術論文集 26 19 - 24 2020 [Refereed]
  • Tsuyoshi HOSHINO, Hiroki OKACHI, Yui TAKEHARA, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 76 (1) 414 - 423 2020 [Refereed]
  • Thu Thanh Nguyen, Makoto Nakatsugawa, Tomohito J. Yamada, Tsuyoshi Hoshino
    Hydrological Research Letters 14 (4) 155 - 161 2020 [Refereed]
  • Sho Kawazoe, Masaru Inatsu, Tomohito J. Yamada, Tsuyoshi Hoshino
    SOLA 16 233 - 239 2020 [Refereed]
  • Tomohito J. Yamada, Yadu Pokhrel
    Atmosphere 10 (11) 725 - 725 2019/11/19 [Refereed]
     
    Irrigation can affect climate and weather patterns from regional to global scales through the alteration of surface water and energy balances. Here, we couple a land-surface model (LSM) that includes various human land-water management activities including irrigation with an atmospheric general circulation model (AGCM) to examine the impacts of irrigation-induced land disturbance on the subseasonal predictability of near-surface variables. Results indicate that the simulated global irrigation and groundwater withdrawals (circa 2000) are ~3600 and ~370 km3/year, respectively, which are in good agreement with previous estimates from country statistics and offline–LSMs. Subseasonal predictions for boreal summers during the 1986–1995 period suggest that the spread among ensemble simulations of air temperature can be substantially reduced by using realistic land initializations considering irrigation-induced changes in soil moisture. Additionally, it is found that the subseasonal forecast skill for near-surface temperature and sea level pressure significantly improves when human-induced land disturbance is accounted for in the AGCM. These results underscore the need to incorporate irrigation into weather forecast models, such as the global forecast system.
  • べイズ手法を用いた信頼区間の将来変化予測-アンサンブル気候予測データへの適用-
    清水 啓太, 山田 正, 山田 朋人
    土木学会論文集B1(水工学) Vol.75 2019/11 [Refereed][Not invited]
  • ベイズ手法に基づくアンサンブル気候予測データを用いた信頼区間の更新
    清水 啓太, 山田 正, 山田 朋人
    水文・水資源学会2019年度研究発表会要旨集 2019/09 [Not refereed][Not invited]
  • 信頼区間・予測区間を導入した水文頻度解析における不確実性評価
    清水 啓太, 山田 正, 山田 朋人
    河川技術論文集 2019/06 [Refereed][Not invited]
  • Dzung Nguyen-Le, Tomohito J. Yamada
    Weather and Forecasting 34 (2) 345 - 360 0882-8156 2019/04/01 [Refereed]
     
    Abstract In this study, self-organizing maps in combination with K-means clustering are used to objectively classify the anomalous weather patterns (WPs) associated with the summertime [May–June (MJ) and July–August–September (JAS)] heavy rainfall days during 1979–2007 over the Upper Nan River basin, northwestern Thailand. The results show that in MJ, intensive rains are mainly brought by the remarkable enhancement of the westerly summer monsoon. Meanwhile, westward-propagating tropical disturbances including tropical cyclones are the primary factors that reproduce heavy rainfall over the Upper Nan in JAS. These results also suggest that the occurrence time of local heavy rainfall is strongly related to the seasonal transition of the summer monsoon over the Indochina Peninsula. The classification results are then implemented with the perfect prognosis and analog method to predict the occurrence (yes/no) of heavy rainfall days over the studied basin in summer 2008–17 using prognostic WPs from the operational Japan Meteorological Agency Global Spectral Model (GSM). In general, the forecast skill of this approach up to 3-day lead times is significantly improved, in which the method not only outperforms GSM with the same forecast ranges, but also its 3-day forecast is better than the 1–2-day forecasts from GSM. However, the false alarms ratio is still high, particularly in JAS. Nevertheless, it is expected that the new approach will provide warning and useful guidance for decision-making by forecasters or end-users engaging in water management and disaster prevention activities.
  • Fujita Mikiko, Sato Tomonori, Yamada Tomohito J, Kawazoe Sho, Nakano Masuo, Ito Kosuke
    JOURNAL OF THE METEOROLOGICAL SOCIETY OF JAPAN 97 (2) 387 - 401 0026-1165 2019/04 [Refereed][Not invited]
  • 岡地寛季, 山田朋人, 渡部靖憲, 猿渡亜由未, 大塚淳一, 森信人, 馬場康之, 久保輝広, 二宮順一, 内山雄介, 水谷英郎
    土木学会論文集 G(環境)(Web) 公益社団法人 土木学会 75 (5) I_41 - I_46 2185-6648 2019 [Refereed]
  • 2016年北海道豪雨災害を対象としたアンサンブル気象予測を用いた河川水位，河床変動及び氾濫形態の予測可能性
    ムハマド イザーズ, ハズミー, ビン スハイミ, 山田朋人, 久加朋子, 清水康行, 奥田醇, 星野剛
    土木学会論文集B1(水工学) 75 1435 - 1440 2019 [Refereed]
  • RESEARCH REPORT ON EXAMINATION AND IMPLEMENTATION STATUS OF CLIMATE CHANGE ADAPTATION IN THE FIELD OF FLOOD CONTROL IN THE NETHERLANDS (2ND REPORT)
    千葉学, 戸村翔, 山本太郎, 植村郁彦, 舛屋繁和, 吉田隆年, 大村宣明, 時岡真治, 佐々木博文, 濱田悠貴, 星野剛, 山田朋人, 中津川誠
    河川技術論文集 25 49 - 54 2019 [Refereed]
  • Tsuyoshi HOSHINO, Tomohito J. YAMADA, Dzung Nguyen-Le
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 75 (5) I_25 - I_31 2185-6648 2019 [Refereed]
  • Sho TOMURA, Shigekazu MASUYA, Fumihiko UEMURA, Takatoshi YOSHIDA, Noriaki OOMURA, Manabu CHIBA, Taro YAMAMOTO, Hirokazu OKABE, Hirofumi SASAKI, Ayaka KOBAYASHI, Tsuyoshi HOSHINO, Tomohito YAMADA, Makoto NAKATSUGAWA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 75 (2) I_1357 - I_1362 2019 [Refereed]
  • Yuta Tamaki, Masaru Inatsu, Tomohito J. Yamada
    Hydrological Research Letters 13 (4) 55 - 61 2019 [Refereed]
  • 髙木 雅史, 森 信人, 二宮 順一, 志村 智也, 内山 雄介, 馬場 康之, 水谷 英朗, 久保 輝広, 渡部 靖憲, 大塚 淳一, 山田 朋人, 猿渡 亜由未
    土木学会論文集. B2, 海岸工学 Journal of Japan Society of Civil Engineers. 土木学会海岸工学委員会 編 土木学会 75 (2) I_61 - 66 2019 [Refereed][Not invited]
  • 猿渡 亜由未, 大塚 淳一, 馬場 康之, 久保 輝広, 水谷 英朗, 志村 智也, 二宮 順一, 山田 朋人, 内山 雄介, 森 信人, 渡部 靖憲
    土木学会論文集. B2, 海岸工学 Journal of Japan Society of Civil Engineers. 土木学会海岸工学委員会 編 土木学会 75 (2) I_67 - 72 2019 [Refereed][Not invited]
  • 馬場 康之, 久保 輝広, 森 信人, 渡部 靖憲, 山田 朋人, 猿渡 亜由未, 大塚 淳一, 内山 雄介, 二宮 順一
    土木学会論文集. B2, 海岸工学 Journal of Japan Society of Civil Engineers. 土木学会海岸工学委員会 編 土木学会 75 (2) I_271 - 276 2019 [Refereed][Not invited]
  • 岡地 寛季, 山田 朋人, 渡部 靖憲, 猿渡 亜由未, 大塚 淳一, 森 信人, 馬場 康之, 久保 輝広, 二宮 順一, 内山 雄介, 水谷 英郎
    地球環境研究論文集 : 地球環境シンポジウム 土木学会 27 41 - 46 2019 [Refereed][Not invited]
  • 信頼区間の導入による確率洪水ピーク流量の不確実性評価― 総合確率法の拡張―
    清水啓太, 山田正, 山田朋人
    土木学会論文集B1(水工学) 2018/11 [Refereed][Not invited]
  • 星野剛, 山田朋人, 稲津將, 佐藤友徳, 川瀬宏明, 杉本志織
    土木学会論文集B1(水工学) 74 (5) I_13 - I_18 2185-467X 2018/11 [Refereed][Not invited]
  • 確率限界法検定に基づく信頼区間を用いた確率洪水ピーク流量の不確実性評価
    清水啓太, 山田正, 山田朋人
    土木学会論文集G(環境) 2018/09 [Refereed][Not invited]
  • 岩井尚人, 山中康裕, 根岸淳二郎, 山田朋人
    水利科学 364 (5) 59 - 80 0039-4858 2018/08 [Refereed][Not invited]
     
    地下水の持続可能な利用は，その保全にとって必要である。地下水を保全す る態度を育むために，小学校教育の中で地下水について学ぶ機会を作ることは，重要なことである。本研究では，小学校高学年生が地下水涵養に関する森 林の機能などの地下水に関する基本的知識を学べる教材を，タンクモデルを参 考にして開発した。教材は，3 段タンクで構成され，森林領域の下にある帯水 層に設置したスポンジが水を貯留し，その水は装置外へゆっくりと流出するよ うになっている。教材で表現したのは，森林は主要な地下水の涵養域であるこ と，地下水は地表水に比べて滞留時間が長いことの 2 つである。教材を用いた 散水実験では，3 段のタンクそれぞれからの流出ピークのタイムラグや滞留時 間の違いなど，上記 2 点を定量的に確認した。小学校等の教員13名を対象に実 施した教材の実演と，彼らに対する聞き取り調査では，多くの教員は，小学校 児童にとって，上記 2 点が分かりやすいと判断した。
  • Yuta Tamaki, Masaru Inatsu, Dzung Nguyen-Le, Tomohito J. Yamada
    Journal of Applied Meteorology and Climatology 57 (7) 1477 - 1496 1558-8424 2018/07 [Refereed]
     
    AbstractDynamical downscaling (DDS) was conducted over Japan by using a regional atmospheric model with reanalysis data to investigate the rainfall duration bias over Kyushu, Japan, in July and August from 2006 to 2015. The model results showed that DDS had a positive rainfall duration bias over Kyushu and a dry bias over almost all of Kyushu, which were emphasized for extreme rainfall events. Investigated was the rainfall duration bias for heavy rainfall days, accompanied by synoptic-scale forcing, in which daily precipitation exceeded 30 mm day−1 and covered over 20% of the Kyushu area. Heavy rainfall days were sampled from observed rainfall data that were based on rain gauge and radar observations. A set of daily climatic variables of horizontal wind and equivalent potential temperature at 850 hPa and sea level pressure, around southwestern Japan, corresponding to the sampled dates, was selected to conduct a self-organizing map (SOM) and K-means method. The SOM and K-means method objectively classified three synoptic patterns related to heavy rainfall over Kyushu: strong monsoon, weak monsoon, and typhoon patterns. Rainfall duration had a positive bias in western Kyushu for the strong monsoon pattern and a positive bias in southern and east-coast Kyushu for the typhoon pattern, whereas there was little rainfall duration bias in the weak monsoon pattern. The bias for the typhoon pattern was related to rainfall events with a strong rainfall peak. The results suggest that bias correction for rainfall duration would be required for accurately estimating direct runoff in a catchment area in addition to the precipitation amount.
  • 北海道における気候変動に伴う洪水外力の変化
    山田朋人, 星野剛, 舛屋繁和, 植村郁彦, 吉田隆年, 大村宣明, 山本太郎, 千葉学, 戸村翔, 時岡真治, 佐々木博文, 濱田悠貴, 中津川誠
    河川技術論文集 24 391 - 396 2018/06 [Refereed][Not invited]
  • M. A. Farukh, Tomohito J. Yamada
    International Journal of Climatology 38 (5) 2230 - 2238 0899-8418 2018/04 [Refereed]
  • Watanuki Akira, Yamada Tadashi
    Proceeding of Annual Conference 水文・水資源学会 31 198  2018 
    Recently, various schemes related to solving water problems have been adopted. As these are common, there is planned management of basins. Therefore, it is necessary to accurately understand the state of the water area through monitoring and simulation. However, in the simulation of lake water temperature, it is very difficult to always keep the difference between observed value and calculated value within 1 ° C throughout the year, and as far as the authors know, such estimation method does not exist. Water temperature is an important water quality item in order to know the properties of lakes. Therefore, in this article, we aim to improve the estimation accuracy of lake water temperature with optimal interpolation method in heat budget method. And we studied on the annual number of days when the difference between the estimation result of water temperature and the mesuared value is within 1 ° C.
  • WATANUKI Akira, YAMADA Tadashi
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 公益社団法人 土木学会 74 (5) I_117 - I_123 2018 [Not refereed]
     
    In this article, we calculated the daily mean water temperature in a shallow lake by the optimal interpolation which is one of the data assimilation methods. We set three kinds of the weight of optimal interpolation to investigate an accuracy of calculation. As a result, the accuracy became quickly worse within 8 days of interplorating interval. In addition, when the interval of 8 days was longer, it was found that 30 to 50% of results by data assimilation was worse than results of heat budget method because results of both no data assimilation and by data assimilation were almost the same within 8 days.
  • Yuta OHYA, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (5) I_229 - I_234 2018
  • 大規模洪水時における内外水同時氾濫解析モデルを用いた時空間的な浸水リスク評価
    米田駿星, 佐藤誠, 川村育男, 渡邊一晴, 松本勝治, 山田朋人
    河川技術論文集 25 43 - 47 2018 [Refereed]
  • Hayase YONEDA, Makoto SATOH, Ikuo KAWAMURA, Masashi YAMAGUCHI, Katsuharu MATSUMOTO, Tomohito YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (5) I_1387 - I_1392 2018
  • 水資源の観点から見た，石狩川中流域に おける稲作の現状と将来への示唆
    金子直広, 山田朋人
    水利科学 62 (3) 52 - 70 2018 [Refereed]
  • Hiroki OKACHI, Tomohito J. YAMADA, Yasunori WATANABE
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (4) I_265 - I_270 2185-467X 2018 [Refereed]
  • Tsuyoshi HOSHINO, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (4) I_187 - I_192 2185-467X 2018 [Refereed]
  • Yuta OHYA, Yoshikazu KITANO, Dzung NGUYEN-LE, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (4) I_43 - I_48 2018 [Refereed]
  • Tsuyoshi HOSHINO, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 74 (5) I_25 - I_31 2185-6648 2018 [Refereed]
  • Yui TAKEHARA, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 74 (5) I_249 - I_255 2018 [Refereed]
  • Fumihiko UEMURA, Shigekazu MASUYA, Takatoshi YOSHIDA, Noriaki OOMURA, Manabu CHIBA, Sho TOMURA, Taro YAMAMOTO, Shinji TOKIOKA, Hirofumi SASAKI, Yuki HAMADA, Tsuyoshi HOSHINO, Tomohito YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (5) I_115 - I_120 2185-467X 2018 [Refereed]
  • Hiroki OKACHI, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (5) I_1201 - I_1206 2018 [Refereed]
  • Nobutaka HOSOI, Tomohito YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (5) I_55 - I_60 2018 [Refereed]
  • Mai ANDO, Tsuyoshi HOSHINO, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (5) I_1249 - I_1254 2185-467X 2018 [Refereed]
  • Shigekazu MASUYA, Fumihiko UEMURA, Takatoshi YOSHIDA, Noriaki OOMURA, Manabu CHIBA, Sho TOMURA, Taro YAMAMOTO, Shinji TOKIOKA, Hirofumi SASAKI, Yuki HAMADA, Tsuyoshi HOSHINO, Tomohito YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (5) I_121 - I_126 2185-467X 2018 [Refereed]
  • H. Okachi, T. J. Yamada, Y. Watanabe, J. Ohtsuka
    International Association for Hydro-Environment Engineering and Research (IAHR)-Asia Pacific Division (APD) Congress: Multi-Perspective Water for Sustainable Development, IAHR-APD 2018. 1 493 - 501 2018 [Refereed][Not invited]
     
    © Proceeding of the 21st LAHR-APD Congress 2018. All rights reserved. Various fluxes are always exchanged at the air-sea surface. Considering flux exchanges in furious storm condition, there are much rain droplets and sea sprays generated from wave breaks. Sea sprays are instantly accelerated by local wind as they are generated. They have substantial mass. Therefore, momentum is conveyed by these droplets from the atmosphere to the ocean Focusing on the raindrops, they have horizontal speed more than wind speed when reaching the near-sea surface. That is, raindrops accelerate horizontal wind speed, however, there is no confirmation. Additionally, sea spray transfers latent heat extracted from the atmosphere in the process of its phase change. In this research, parameterization of momentum exchange at the air-sea surface is reconsidered concerning about drag coefficient. The drag coefficient increases as wind speed increases. We propose an equation which includes the effect of raindrops on the equation of drag coefficient that takes into account of sea spray and the characteristics of momentum exchange coefficient related to rainfall intensity and wind velocity. We also perform marine observation from 2013 to 2016 at an observational tower in Wakayama-prefecture, Japan, where typhoon often hits. Several typhoons passed near the tower for four years. We further conduct wind tunnel experiments to directly observe sea sprays (diameter > 72 μm) for six high wind speed conditions (U10=23∼28m/s).
  • Keita SHIMIZU, Tomohito YAMADA, Tadashi YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 74 (4) I_331 - I_336 2018 [Refereed][Not invited]
  • SARUWATARI Ayumi, MORI Nobuhito, WATANABE Yasunori, SAKAGAWA Ryota, OTSUKA Junichi, BABA Yasuyuki, KUBO Teruhiro, MIZUTANI Hideaki, NINOMIYA Junichi, YAMADA Tomohito, UCHIYAMA Yusuke
    Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) 公益社団法人 土木学会 74 (2) I_67 - I_72 1884-2399 2018 [Refereed][Not invited]
  • OKADA Nobue, OTSUKA Junichi, YAMADA Tomohito, SARUWATARI Ayumi, NINOMIYA Junichi, UCHIYAMA Yusuke, TADA Hiroaki, ENDO So, BABA Yasuyuki, MIZUTAMI Hideaki, KUBO Teruhiro, MORI Nobuhito, WATANABE Yasunori
    Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) 公益社団法人 土木学会 74 (2) I_667 - I_672 1884-2399 2018 [Refereed][Not invited]
  • Dzung Nguyen-Le, Tomohito J. Yamada, Duc Tran-Anh
    ATMOSPHERIC SCIENCE LETTERS 18 (8) 324 - 329 1530-261X 2017/08 [Refereed][Not invited]
     
    In this study, the Self-Organizing Maps in combination with K-means clustering technique are used for classification of synoptic weather patterns inducing heavy rainfall exceeding 100mmday(-1) during the Baiu season (June-July) of 1979-2010 over northern Kyushu, southwestern Japan. It suggests that these local extreme rainfall events are attributed to four clustered patterns, which are primarily related to the Baiu front and the extratropical/tropical cyclone/depression activities and represented by the intrusion of warm and moist air accompanied by the low-level jet or cyclonic circulation. The classification results are then implemented with the analogue method to predict the occurrence (yes/no) of local heavy rainfall days in June-July of 2011-2016 by using the prognostic synoptic fields from the operational Japan Meteorological Agency (JMA) Global Spectral Model (GSM). In general, the predictability of our approach evaluated by the Equitable Threat Score up to 7-day lead times is significantly improved than that from the conventional method using only the predicted rainfall intensity from GSM. Although the false alarm ratio is still high, it is expected that the new method will provide a useful guidance, particularly for ranges longer than 2 days, for decision-making and preparation by weather forecasters or end-users engaging in disaster-proofing and water management activities.
  • Yoshitaka Sakata
    Journal of JSCE 72 (5) 253 - 264 2017/02 [Refereed][Not invited]
  • Hoshino Tsuyoshi, Yamada Tomohito
    Proceeding of Annual Conference 水文・水資源学会 30 12 - 12 2017 
    2016年8月，4つの台風が北海道に相次いで接近・上陸し，全道各地に記録的な大雨をもたらした．これにより，氾濫や橋脚の流出などの大雨による被害が広域的に発生し，北海道だけでなく全国的にも前例のないほどの極めて深刻な水害となった。この記録的豪雨の背景には気候変動の影響が考えられ，気候変動へ適応した新しい水防災対策の構築が喫緊の課題として顕在化した．本研究ではこの新しい水防災対策を構築する上で基礎となる気候変動による流域内の降水量の変化を明らかにすることを目的に，気候予測データベース(d4PDF)に基づいて流域内の降水量を評価した．
    十勝川流域において流域平均3日降水量，流域平均10日降水量を調べたところ，どりらも温暖化により降水量が増大する傾向にあり，気候変動により大雨の高頻度化および激甚化が引き起こされることが示唆された．また，流域平均10日降水量も増大していたことから気候変動を踏まえた水防災対策の構築するに当たっては土壌水分量の考慮の重要性がより一層高まるものと考えられる．
  • Kitano Yoshikazu, Yamada Tomohito J.
    Proceeding of Annual Conference 水文・水資源学会 30 8 - 8 2017 
    中緯度における気象擾乱がもたらす極端現象の要因の一つとして，大気ブロッキングが挙げられる．ブロッキングは，移動性高気圧よりもスケールの大きな高気圧が高緯度側に張り出し，大気中上層において通常とは逆転した南北ジオポテンシャル高度勾配，温位勾配が一地域に一定期間（多くの研究では5日程度）継続した場合同定される．また，ブロッキングの強度は，ブロッキング高気圧と周囲との気圧差やブロッキング高低気圧間に形成される東風の強さで定義される．本研究は，Rossby (1950)が提唱し，Armi (1989)，Riffler (2005)により室内実験・現実大気のデータで検証された偏西風が有する比エネルギーの理論を用い，ブロッキングの流れ場が有する比エネルギーの大小からブロッキングを物理的に定義することを目的とする。ジェット気流が有する比エネルギーの式を現実大気場に適用可能とし、ブロッキングが発生するために必要な同エネルギーの下限値を導き出した。
  • Ohya Yuta, Nagao Kenta, Yamada Tomohito
    Proceeding of Annual Conference 水文・水資源学会 30 28 - 28 2017 
    複数のドップラーレーダと変分原理を用いることによって大気の三次元場の議論が可能になる．本研究では，気象庁によって設置・管理されている２基のCバンドレーダを用い，2014年9月に札幌圏で発生した線状降水帯を対象に降水を伴う気象場を分析した．三次元的な風速場の解明によって線状降水帯などの予測及び対策を可能にし，大規模災害を防ぐことに役立つと考えられる．
    使用した手法は，航空機搭載型のレーダによる観測のため考案され，その後地上レーダに特化した手法である．同手法は３項からなる二次元変分法を用いて計算する。 3項はそれぞれ極座標系から直交座標への内挿を行う項，質量保存項，平滑化項である.
    解析対象は，札幌近郊に住む90万人に避難勧告が出され北海道で初となる特別警報となった2014年9月11日の豪雨である．観測結果を同化し日本付近の大気場を補間した気象庁数値モデルと比較した場合，レーダ解析の結果からはより詳細な風速ベクトルを検知でき，線状降水帯の南東に位置の降水域で大気の水平鉛直循環を発見した．また強い反射強度を示す部分では上昇気流が発生し深い積乱雲の構成に寄与していることも示唆された．
  • Kobayashi Ayaka, Shibata Kounosuke, Nguyen-Le Dzung, Yamada Tomohito
    Proceeding of Annual Conference 水文・水資源学会 30 39 - 39 2017 
    2016年8月の約2週間に4度の台風による豪雨で，北海道内では年降水量に匹敵する降雨量を記録し，河川氾濫や土砂災害等の甚大な災害が発生した．台風10号の大雨により, 南富良野町では堤防決壊及び河川氾濫が発生した. 本研究では, 南富良野町を含む空知川上流部に位置する金山ダムを対象流域とし，台風10号時の降雨流出特性を述べる．

    河川整備計画や防災対策は主に地上雨量観測値を用いて行われている．雨量計とは，地上に到達した雨滴を直径20cmの転倒マスで計測するものである．北海道の一級水系流域においては114km2に1つある計算となる．しかし，豪雨をもたらす積乱雲の空間スケールが数kmであり，山間部は地形による降雨強度の時空間的なばらつきが大きい特徴を有することを考慮すると，雨量計の存在する位置により総降雨量の観測値にばらつきが生じる. 一方, レーダー雨量計は面的かつ高解像度での観測が可能だが，間接的に降水強度を推定していることなどにより, 精度限界が存在する．これら２つの観測手法を組み合わせた解析雨量が存在する．解析雨量はレーダーで観測した面的なデータを，地上雨量との比較で補正したものである．本研究で用いる降雨データは，国交省C-band，気象庁C-band，地上雨量計(アメダス及び国土交通省保有のもの)及び解析雨量である．

    本研究は，降雨観測位置による不確実性について検討し，それらが対象流域に与える不確実性を定量化，さらには気象モデルによる2日前からの気象予測結果と比較, 検討をした．
  • Yoshikazu KITANO, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 土木学会 73 (4) I_439 - I_444 1880-8751 2017 [Refereed]
  • Yoshikazu KITANO, Taro YAMAMOTO, Ayaka KOBAYASHI, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 土木学会 73 (4) I_1231 - I_1236 1880-8751 2017 [Refereed]
  • Dzung NGUYEN-LE, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 土木学会 73 (4) I_199 - I_204 1880-8751 2017 [Refereed]
  • Yuta OHYA, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 土木学会 73 (5) I_269 - I_274 2017 [Refereed]
  • Yoshikazu Kitano, Tomohito J. Yamada
    Atmospheric Science Letters Wiley-Blackwell 17 (11) 616 - 622 1530-261X 2016/11 [Refereed]
     
    Atmospheric blocking is one of the most impactful weather patterns in midlatitude regions, causing floods, droughts and unusually high or low temperatures. This study investigates the relationship between extremely cold days over Japan and its surroundings and North Pacific blocking in the European Centre for Medium-rangeWeather Forecasts (ECMWF) re-analysis (ERA-40), phase 5 of the Coupled Model Intercomparison Project (CMIP5) for historical weather and the representative concentration pathway 8.5 (RCP8.5) experiments based on nine climate model datasets in the boreal winter season. Under the climate change conditions based on the RCP8.5 future scenario, extreme cold days (i.e. the first percentile of cold days) over Japan and its surroundings will become weaker but occur more widely when blocking is generated over the northwestern Sea of Okhotsk and its surroundings, because the blocking frequency over this area will decrease and the intensity will weaken.
  • Tomohito J. Yamada, Daiki Takeuchi, M. A. Farukh, Yoshikazu Kitano
    JOURNAL OF CLIMATE 29 (21) 7743 - 7754 0894-8755 2016/11 [Refereed][Not invited]
     
    Pakistan and northwestern India have frequently experienced severe heavy rainfall events during the boreal summer over the last 50 years including an event in late July and early August 2010 due to a sequence of monsoon surges. This study identified five dominant atmospheric patterns by applying principal component analysis and k-means clustering to a long-term sea level pressure dataset from 1979 to 2014. Two of these five dominant atmospheric patterns corresponded with a high frequency of the persistent atmospheric blocking index and positive sea level pressure over western Russia as well as an adjacent meridional trough ahead of northern Pakistan. In these two groups, a negative sea surface temperature anomaly was apparent over the equatorial mid-to eastern Pacific Ocean. The heavy precipitation periods with high persistent blocking frequency in western Russia as in the 2010 heat wave tended to have 1.2 times larger precipitation intensity compared to the whole of the heavy precipitation periods during the 36 years.
  • M. Yokokawa, N. Izumi, K. Naito, G. Parker, T. Yamada, R. Greve
    Journal of Geophysical Research: Earth Surface American Geophysical Union (AGU) 121 (5) 1023 - 1048 2169-9003 2016/05 [Refereed]
     
    Boundary waves often form at the interface between ice and fluid flowing adjacent to it, suchas ripples under river ice covers, and steps on the bed of supraglacial meltwater channels. They may alsobe formed by wind, such as the megadunes on the Antarctic ice sheet. Spiral troughs on the polar ice capsof Mars have been interpreted to be cyclic steps formed by katabatic wind blowing over ice. Cyclic stepsare relatives of upstream-migrating antidunes. Cyclic step formation on ice is not only a mechanical butalso a thermodynamic process. There have been very few studies on the formation of either cyclic steps orupstream-migrating antidunes on ice. In this study, we performed flume experiments to reproduce cyclicsteps on ice by flowing water, and found that trains of steps form when the Froude number is larger thanunity. The features of those steps allow them to be identified as ice-bed analogs of cyclic steps in alluvial andbedrock rivers. We performed a linear stability analysis and obtained a physical explanation of the formationof upstream-migrating antidunes, i.e., precursors of cyclic steps. We compared the results of experimentswith the predictions of the analysis and found the observed steps fall in the range where the analysispredicts interfacial instability. We also found that short antidune-like undulations formed as a precursor tothe appearance of well-defined steps. This fact suggests that such antidune-like undulations correspondto the instability predicted by the analysis and are precursors of cyclic steps.
  • 吉見和紘, Chao-Wen WANG, 山田正, 山田朋人
    土木学会論文集B1（水工学） 72 (4) 2185-467X 2016/03 [Refereed][Not invited]
  • WATANUKI Akira, YAMADA Tadashi
    Proceeding of Annual Conference 水文・水資源学会 29 87  2016 
    The heat budget method is often used as a method to estimate water temperature. But meteorological data at two altitudes are needed to calculated sensible and latent heat fluxes using the gradient method and the Bowen ratio energy balance method. And the bulk method is able to calculate those at one altitude with meteorological data but bulk transfer coefficient must be generally given and atmosphere stability is calculated as neutrality. In this article, we calculated sensible and latent heat fluxes using the iterative approximation method, the bulk method and Kondo's theory at one altitude with meteorological data and estimated daily mean water temperature. As a result, the prediction didn't improve.
  • WANG Chao-Wen, YOSHIMI Kazuhiro, YAMADA Tadashi, YAMADA Tomohito
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 72 (4) I_1279 - I_1284 1880-8751 2016 [Not refereed]
     
    Most of the past studies on the analysis of landslides are evaluated by determinism. It means the analysis are only two results, stable and unstable. However in the real environment, there are a lot of uncertainty factors that would affect the occurrence of landslides. In the study, the authors consider the hydrological uncertainty and the variability of soil parameters of the slope to propose a new method for the risk evaluation of landslide induced by rainfall. The uncertainty has two types, one is the limitation of observation or experiment and the other one is and the error of data. For the landslides analysis, the uncertainty analysis can be separated by the external force from rainfall and the resistance force of slope stability. In considering the external force, it would focus on the analysis the relationship between rainfall and storage by using storage function model based on the uncertainty rainfall and the analysis of slope stability would consider the deviation of the soil parameters. Finally the occurrence of landslides can be summarized as like the risk evaluation during rainfall based on the stochastic process theory.
  • Tao Lu, Tomohito Yamada, Tadashi Yamada
    12TH INTERNATIONAL CONFERENCE ON HYDROINFORMATICS (HIC 2016) - SMART WATER FOR THE FUTURE 154 88 - 93 1877-7058 2016 [Refereed][Not invited]
     
    This study focuses on the improvement of the accuracy and construction of a real-time, short-term rainfall prediction system in watershed, comparing the prediction results with radar observed rainfall intensity, to provide a reliable tool for disaster and water resource management. The short-term prediction of rainfall is very important for hydrologie forecasting for watershed with a short response time, especially under the global warming and extreme weather. Last September 9th (2015), heavy rain came a day after Tropical Storm Etau and triggered widespread flooding in Kinu Watershed. We use the Weather Research and Forecasting Model (WRF) to confirm the uncertainty of the rain prediction in Kinu watershed first, then will modify the WRF to suit the 6h, 12h, 24h rainfall prediction in Kinu watershed. Also, radar rainfall data will be employed to correct the WRF prediction in real-time meaning. Finally, we will check the possibility of general application of the system in other watersheds. We now are working on reproducing the heavy rain in Kinu watershed last September. We tried different microphysics, which describes the formation of cloud, to find one to reproduce the heavy rain in this case. The coverage, location of rain bands and distribution of heavy rainfall are applied to comparisons between calculations and observations by C-band radar. We found no Microphysics does well in this case and the area of heavy rain is underestimated by WRF, but the accumulated precipitation is overestimated. Detail insight at microphysics and modification are required. (C) 2016 The Authors. Published by Elsevier Ltd.
  • Daiwei Cheng, Yoshimasa Morooka, Tadashi Yamada, Tomohito J. Yamada
    2016 3RD INTERNATIONAL CONFERENCE ON SYSTEMS AND INFORMATICS (ICSAI) 603 - 608 2474-0217 2016 [Not refereed][Not invited]
     
    Rainfall-runoff process is the central issue of hydrology. The prediction of the runoff has many practical significances. In 1974, M. Hino had firstly applied the Kalman filter in forecasting the rainfall- runoff process, since then many new filters had been suggested and applied in rainfall- runoff process. However, there is no filter can help to recognize the physical meaning of the random external force. On the other hand, recently, K. Yoshimi and T. Yamada have tried to use Fokker-Planck equation to study the uncertainty of stream flow due to the random fluctuation in precipitation. And this can be used in the filter theory to deal with nonlinear systems and also to find the physical meaning of the system noise. The present study is based on K. Yoshimi and T. Yamada's work, aimed at directly using Fokker-Planck equation in the prediction step of filtering, and applied it in the rainfall-runoff process
  • Cheng Daiwei, Yamada Tadashi, Yamada Tomohito
    Proceeding of Annual Conference 水文・水資源学会 29 128 - 128 2016 
    When dealing with the hydrological system, it is very hard to use the first principle directly because of the large scale of the system. So modeling and simplify has to be done. However, there are information neglected by these models and it causes the uncertainty when people want to predict the system. A lot of research had been done in order to solve the above problem. For example, Yoshimi and Yamada had tried to consider the uncertainty of rainfall as a kind random external force of the rainfall-runoff system and to explain the system by stochastic differential equation. However, the infiltration process has not been considered in their study This study is based on Yoshimi and Yamada’s work and aimed at find out the how the uncertainty of rainfall affects the runoff when you consider the infiltration process.
  • Yoshikazu KITANO, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 72 (4) I_121 - I_126 2016 [Refereed][Not invited]
  • Yoshikazu KITANO, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 72 (5) I_233 - I_239 2016 [Refereed]
  • Yoshikazu Kitano, Tomohito J. Yamada
    Procedia Engineering 154 726 - 732 1877-7058 2016 [Refereed]
  • SARUWATARI Ayumi, WATANABE Yasunori, YAMADA Tomohito, OTSUKA Junichi, BABA Yasuyuki, MIZUTANI Hideaki, KUBO Teruhiro, UCHIYAMA Yusuke, MORI Nobuhito, NINOMIYA Junichi
    Journal of Japan Society of Civil Engineers, Ser. A2 (Applied Mechanics (AM)) 公益社団法人 土木学会 72 (2) I_537 - I_547 2185-4661 2016 [Refereed][Not invited]
     
    Sea spray is one of the important factors to affect weather conditions over the ocean in terms of constituting an aerosol as well as determining air-sea transport of heat, moisture and momentum. The final goal of this study is to explain the relationship between sea-spray generation and conditions of the atmosphere and ocean for a more accurate prediction of the amount of sea spray. This study conducted three-year field observations of atmospheric aerosol at an offshore observatory in Tanabe Bay, Wakayama. Large-scale (> 100 km) distribution of atmospheric aerosol was found to dominate the concentration of the observed aerosol less than 1 μm in normal weather conditions. During storm events with strong winds from the Pacific Ocean, however, the observed concentration monotonically increased with the wind speed, which is considered to be a result of the increase in oceanic aerosol derived from sea spray.
  • KUBO Shinya, NINOMIYA Junichi, MORI Nobuhito, BABA Yasuyuki, MIZUTANI Hideaki, KUBO Teruhiro, UCHIYAMA Yusuke, WATANABE Yasunori, YAMADA Tomohito, OTSUKA Junichi, SARUWATARI Ayumi
    Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) 公益社団法人 土木学会 72 (2) I_487 - I_492 1883-8944 2016 [Refereed][Not invited]
     
     This study focuses on the process of thermocline's destruction and reformation during typhoons using field observation data. The thermocline has a large effect on the circulation and would be a factor to make water worse. Therefore, it is necessary to understand its process deeply. In this study, the stability of density stratification was evaluated based on the Brant-Vaisala frequency and the Richardson number. The results suggested that high wave destroyed the stratification and high wind mixed ocean water vertically more energetically during stratified season. On the other hand, is was found that stratification was unstable regardless of typhoon intensity during unstratified season. Moreover, the characteristics of water-mass were evaluated on the TS diagram during unstratified season.
  • UCHIYAMA Yusuke, YOSHIKI Tomomichi, TADA Hiroaki, BABA Yasuyuki, MIZUTANI Hideaki, KUBO Teruhiro, MORI Nobuhito, SARUWATARI Ayumi, OTSUKA Junichi, NINOMIYA Junichi, WATANABE Yasunori, YAMADA Tomohito
    Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) 公益社団法人 土木学会 72 (2) I_493 - I_498 1884-2399 2016 [Refereed][Not invited]
     
     For rigorious description of upper ocean dynamics and resultant volume transport at the mouth of Tanabe Bay, Wakayama, Japan, a comprehensive field campaign was conducted from summer to fall of 2015. The vertical structure of transient dynamics in the surface boundary layer and consequent water exchange at the mouth are characterized by high-frequency variability peaked at around the semi-diurnal period as well as in the lower-frequency subtidal band centered at 3 day period, consistent with the previous modeling study. A spectral coherence analysis indicates that near-surface currents are mainly driven by wind stress peaked at the diurnal frequency, whereas subsurface currents fluctuate rather by semi-diurnal internal tides. The upper ocean cools down gradually, corresponding to seasonal transition from summer to fall condition. However, an abrupt cooling event is observed albeit in a calm local forcing condition where an offshore subtidal cold water intrusion induced remotely by the fluctuating Kuroshio path plays an essential role.
  • Chao-Wen WANG, 吉見和紘, 山田正, 山田朋人
    土木学会論文集G（環境） 公益社団法人 土木学会 71 (5) I_1 - I_6 2185-6648 2015/09 [Refereed][Not invited]
     
    Most of the past studies on the levee destruction are determinism that for the different flood conditions the levee is failure or not failure. However in the real environment, there are a lot of uncertainty factors that would affect the analysis result of the levee stability very seriously. In this study, the authors would consider the variability of soil parameters of levee and propose the new idea for the reliability evaluation of levee during floods by using the probability theory.
     In consideration of the different water level conditions, the probability of safety factor of levee can be estimated. When the levee is completely saturated, the safety factor is 80% smaller than 1.2 with considering the uncertainty of the soil parameters in the levee with 7.5 m height. And another water levels, like 7.50 m, 7.25 m and 7.0m is be estimated, here the high water level is 7.0 m assumed.
     In conclusions, with considering the variability of the soil parameters, the safety factor of levee is a distribution. Furthermore the driving force and resistance force of levee can be summarized as the reliable design analysis. Finally in this study, the risk of flood (including of levee destruction and overflow) can be evaluated with the change of water level.
  • 崔 瑂芝, 佐々木 翔太, 吉見 和紘, 山田 正, 山田 朋人
    第23回地球環境シンポジウム講演集 土木学会 23 189 - 192 2015/09 [Not refereed][Not invited]
  • 吉見和紘, 山田正, 山田朋人
    土木学会論文集B1(水工学) 公益社団法人 土木学会 71 (1) I_259 - I_264 2185-467X 2015/03 [Refereed][Not invited]
     
    This paper explained the uncertainty of discharge due to the uncertainty of rainfall theoretically and mathematically. The lumped rainfall-runoff model is represented by SDE (stochastic differential equation), because the temporal variation of rainfall is expressed by its average plus deviation, which is approximated by Gaussian distribution. As a result, this paper has shown that it is possible to evaluate the uncertainty of discharge by using the relationship between SDE and Fokker-Planck equation. Moreover, the results of this study show that the uncertainty of discharge increases as rainfall intensity rises and non-linearity about resistance grows strong. These results are clarified by PDFs (probability density function) that satisfy Fokker-Planck equation about discharge. It means the reasonable discharge can be estimated based on the theory of stochastic processes, and it can be applied to the probabilistic risk of flood management.
  • QIAN Chaochao, YAMADA Tadashi
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 公益社団法人 土木学会 71 (5) I_283 - I_288 2015 [Not refereed]
     
    Numerical calculations of climate change and weather forecast has been widely carried out, and Monin-Obukhov length based vertical distribution of wind velocity (Log+Linear law) is used in the calculations typically. However, it is not suitable for the numerical calculations because the stability scale of Monin-Obukhov is an algebraic expression. Also, it is very difficult to give a physical interpretation that the scale of the mixing length is negative when the atmosphere is instable. In addition, the scale on the vertical direction of the mixed layer should be set a priori when the atmosphere is instable. In order to solve these problems, a new differential equation of physically rigorous mixing length with considering atmospheric stability has been proposed in this study. The precision of wind velocity distribution in the vertical direction was confirmed by both observed data and Monin-Obukhov length bese Log+Linear law in the study. The proposed stability length can be used more conveniently than existing Monin-Obukhov length based mixing length to deal with the boundary layer in atmospheric calculations such as GCM or weather models.
  • Ichinose Rinko, Kitano Yoshikazu, Yamada Tomohito, Watanabe Yasunori, Izumi norihiro
    Proceeding of Annual Conference 水文・水資源学会 28 100131  2015 
    The weather condition in the middle latitudes is controlled by westerly wind and high and low pressures, and these phenomena are interpreted as the baroclinic instability waves. A rotating fluid experiment by Fultz and Hide are known as the typical laboratory experiments of baroclinic instability waves. In this study, we introduced a new equipment having the unique feature characterized by the heated and cooled bottom. By this condition, 4-6 zonal wave numbers were observed and flow field were dynamically changed with time. At the sametime, it was observed that the vorticity on center changed with baroclinic waves with time.
  • YOSHIMI Kazuhiro, WANG Chao-Wen, YAMADA Tadashi, YAMADA Tomohito
    Proceeding of Annual Conference 水文・水資源学会 28 100107  2015 
    In this paper, we showed a theoretical framework to evaluate uncertainties of runoff process based on the theory of stochastic process. If a runoff model can be expressed an ordinary differential equation such as the storage-function, we can rewrite it as a stochastic differential equation (SDE) to include disordered component of rainfall. Moreover we can obtain the time evolution of probability density function about discharge from the correspondence relationship between SDE and the Fokker-Planck equation. Through means of this, we could show the uncertainty of discharge caused by rainfall uncertainty theoretically. This result shows the chance of introduction of this concept into river planning.
  • Satoshi Nishimura, Tetsuya Tokoro, Tomohito Yamada, Norihiro Izumi, Maria Fernanda Rivas
    6th Japan-China Geotechnical Symposium, SJGS 2015 34 - 39 2015 
    Mechanical stability of embankments such as road embankments and river dykes is significantly influenced by their internal hydraulic states, as represented by phreatic surface location and pore water pressure distribution. The mass transfer across the embankment surfaces through water infiltration and evapotranspiration, and the internal migration of pore water to/from foundation soil layers are considered to play a major role in dictating the evolution of the hydraulic state. This paper reports a case study in which hydraulic state variations in an embankment in Hokkaido were monitored over 9 months, including a winter period with ground surface freezing and a significant snow cover. The studied embankment was relatively new, constructed with artificially mixed clay and sand which were generated by nearby excavation. The monitoring records indicate a consistent trend of under-drainage to the foundation layer all during the 9 months, with the pore water pressure at deeper parts registering minimum values during winter and reaching maxima during summer. Explanations for this and other observed features were sought by performing unsteady unsaturated seepage flow analysis with some assumed surface input models. Although the adopted models are fairly crude, the analysis results offer important insights into factors that govern the hydraulic state of low-permeability embankment in snowy cold regions.
  • Tomohito J. YAMADA, Koki WACHI, Eiichi SUZUKI
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 土木学会 71 (5) I_55 - I_60 2015 [Refereed]
  • Daiki TAKEUCHI, Tomohito J. YAMADA, Yadu N. POKHREL
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 土木学会 71 (5) I_189 - I_196 2015 [Refereed]
  • Akihiro SUZUKI, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 土木学会 71 (5) I_257 - I_262 2015 [Refereed]
  • Rinko ICHINOSE, Yoshikazu KITANO, Tomohito. J. YAMADA, Yasunori WATANABE, Norihiro IZUMI
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 土木学会 71 (5) I_289 - I_294 2015 [Refereed]
  • Intan SUPRABA, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 土木学会 71 (5) I_17 - I_22 2015 [Refereed]
  • Syota SASAKI, Hayase YONEDA, Tadashi YAMADA, Tomohito J. YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 土木学会 71 (4) I_49 - I_54 1880-8751 2015 [Refereed]
  • Inatsu Masaru, Sato Tomonori, Yamada Tomohito J, Kuno Ryusuke, Sugimoto Shiori, Farukh Murad A, Pokhrel Yadu N, Kure Shuichi
    Atmospheric Science Letters 16 (3) 297 - 304 2015 [Refereed][Not invited]
     
    © 2015 Royal Meteorological Society. The experiments with three general circulation models (GCMs) by three regional atmospheric models (RAMs) for the dynamical downscaling (DDS) have been performed to evaluate the uncertainty in the global warming response during summertime in Hokkaido, Japan. The results of a 10-year RAM integration nested into GCM under present or future climate conditions were synthesized after applying bias correction. For the target decades during which the global-mean temperature increases by 2K in each GCM, the DDS results indicate that surface air temperature and precipitation mostly depend on the GCM imposed as the lateral boundary condition.
  • SUPRABA Intan, YAMADA Tomohito J
    水工学論文集 土木学会水工学委員会 編 土木学会 59 (4) I_151 - 156 1880-8751 2015 [Not refereed][Not invited]
     
    The majority of water catchments in Japan are located in mountainous areas that can produce large quantities of runoff, which may lead to flooding, erosion, and landslides. Thus, it is important to know the minimum total rainfall required to generate surface runoff by estimating the water storage capacity of each catchment. The threshold of minimum total rainfall required to generate surface runoff occurs when at least 95% of total rainfall becomes total loss rainfall such as infiltrates into the ground. The variation in this value is dependent on the catchment characteristics. Based on the relationship between total rainfall and total loss rainfall, the average values of minimum total rainfall required to generate surface runoff and total loss of saturated rainfall were 51.3 mm and 108.5 mm, respectively. Catchments consisting of a smaller area of sedimentary rock and higher values of drainage density, elongation ratio, and catchment width tended to have smaller values of minimum total rainfall required to generate surface runoff.
  • M. A. Farukh, Tomohito J. Yamada
    ATMOSPHERIC SCIENCE LETTERS 15 (4) 259 - 265 1530-261X 2014/10 [Refereed][Not invited]
     
    Synoptic-scale atmospheric circulations are crucial for extreme snowfall events. On the basis of topmost 100 snowfall intensity days in Sapporo, Hokkaido, Japan over winter seasons from 1992 to 2011, this study uses principal component analysis and K-means clustering to characterize synoptic circulation patterns. Composite maps were constructed for sea-level pressure, 850 hPa moisture and wind field, and 500 hPa geopotential height. The circulation patterns of the topmost seven snowfall events were triggered by the advection of very cold airmass from eastern Siberia, anomalously huge moisture with northerly strong wind, active and stationary Aleutian low, and 500 hPa deep cold-core low over the southern Hokkaido.
  • SASAKI SHOTA, YAMADA TADASHI, YAMADA TOMOHITO
    水文・水資源学会誌 THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES 27 (4) 170 - 181 0915-1389 2014/07/05 [Not refereed][Not invited]
     
    This study provides a readily comprehensible hydrology-based model for estimation of the number of radioactive isotopes in the human body, intensity of radioactivity, and internal total exposure without the need for consideration of any complicated mechanism. For example, the International Commission on Radiological Protection has developed an exact model, which is regarded by radiologists as the standard method. However, that method is too complex for non-professional researchers of radiology, including hydrologists, to understand. In contrast, here we calculate the exposure attributable to the ingestion of radioactive isotopes by regarding the human body as a single tissue. Although this study does not involve consideration of a complicated mechanism, it does provide results with accuracy equal to the measured values of intensity of radioactivity obtained using a whole body counter.
  • QIAN Chaochao, YAMADA Tadashi
    Water Science 一般社団法人 日本治山治水協会 58 (1) 64 - 99 0039-4858 2014
  • WATANABE Yamato, YAMADA Tomohito, SUSENO Dwi Prabowo Yuga, SAKOLNAKHON Kamol P.N., TONJAN Somkuan, CHAIYASAN Chatchai
    PROCEEDINGS OF THE JAPANESE CONFERENCE ON HYDRAULICS Japan Society of Civil Engineers 70 (4) I_313 - I_318 2185-467X 2014 
    Chao Phraya river basin is one of the largest basins in the Indochina Peninsula where is located at the South East Asian monsoon region. This study focuses on the diurnal patterns of several cloud types in the rainy season especially during June to August. We used MTSAT (Multi-functional Transport Satellite) Infra-red information from which we classified the clouds into 7 types and then analyzed diurnal characteristics of each cloud type especially in the years 2010 and 2011. 2010 was a drought year and clouds appeared earlier than in the climatology (1996-2011) and 2011, on the other hand, was a flood year and clouds appeared approximately 1 hour later than in the climatology. We obtained results which showed all types of clouds had each diurnal pattern of appearance. Furthermore, those patterns were similar between 2010 and 2011, however they shifted a few hours earlier in 2011 than in 2010.
  • KITANO Yoshikazu, YAMADA Tomohito
    Proceeding of Annual Conference 水文・水資源学会 27 100121 - 100121 2014 
    In middle latitudes, atmospheric blocking is one of the crucial meteorological phenomena. It has a persistent feature leading to extreme events such as heat waves , cold waves , drought and severe precipitation over the surrounding area. The purpose of this study is to reveal the relationship between atmospheric blocking and climate change effects. Mainly, we discuss the change of temperature distribution in mid-latitudes and blocking indexes.
  • Sakata Yoshitaka, Chikita Kazuhisa, Nakatsukawa Makoto, Yamada Tomohito, Kudo Keisuke, Koike Akio, Hamahara Yoshinari, Kimura Mineki, Usutani Tomohide, Uehara Hiroyuki
    Proceeding of Annual Conference 水文・水資源学会 27 100049 - 100049 2014 
    We make an oral presentation of activity results of the research group JSHWR 2013, "Present and future distributions of specific drought rate in Hokkaido, Japan." The purpose of this group is to map present and future specific rates at drought periods in Hokkaido, using an amout of hydrologic and climate data, field measurements in no gauging areas, and spatial analyses based on GIS. The main works in 2013 were to prepare the past hydrologic and climate data over the half century, and to convert the data into GIS format. Other works such as GIS and trend analyses were made only on trial. The conferences were held at 27 May 2013, 26 December 2013, and 20 February 20 2014 to discuss the methods and plans for this research.
  • Yoshikazu KITANO, Tomohito YAMADA, Norihiro IZUMI
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) Japan Society of Civil Engineers 70 (4) I_871 - I_876 2185-467X 2014 [Refereed]
     
    Schmid & Henningson discussed the point disturbance in the homogeneous medium of piecewise linear boundary layer using the method of stationary phase. In addition to this study, we include the density profile to consider the inhomogeneous boundary layer like atmospheric boundary layer. We assume first that the fluid is inviscid and incompressible, density being convected but not diffused. Then the fundamental equations are the Navier-Stokes equations, continuity equation and incompressibility equation and we derive the 3-dimentional Taylor-Goldstein equation. Under the Boussinesq approximation, we obtain the exact solution about the point disturbance propagation on the arbitrary horizontal plane. Using internal Froude number, we explain the characteristics of the solutions.
  • Taiki FUKUSHIMA, Tomohito YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) Japan Society of Civil Engineers 70 (4) I_529 - I_534 2185-467X 2014 [Refereed]
     
    This paper discussed estimation method of probable maximum value of extreme precipitation. We analyzed the 99th percentile of 10-minutes and 1-hour precipitation for each daily average temperature bin based on observational data in Sapporo. Even if temperature is lower than zero degrees, 99th percentile precipitation intensities tend to have an approximation equation that rate of the precipitation increase was almost same as the Clausius-Clapeyron like relation. We estimated the future 99th percentile rainfall intensity under climate change condition by using the projected future temperature in a dynamically downscaled temperature in the Regional Spectral Model (RSM).
  • OTSUKA JUN'ICHI, WATANABE YASUNORI, TASHIRO KOKI, OYAMA TAKAHIRO, SARUWATARI AYUMI, YAMADA TOMOHITO
    土木学会論文集 B2(海岸工学)(Web) Japan Society of Civil Engineers 70 (2) I.41-I.45 (J-STAGE) - I_45 1883-8944 2014 [Not refereed][Not invited]
     
    Sprays and air bubbles formed during wind wave breaking events under various wind conditions were simultaneously visualized using two high-speed video cameras and a back-light imaging technique. The shapes of the sprays and entrained bubbles were quantitatively measured on the basis of novel level-set image detecting algorithm. Spectrum slope of spray and bubble size were found to decrease from approximately 2.2 mm and 1.5 mm respectively. It was also found that the volume rate and wind-wave Reynolds number (RB), the number density and RB are both related to positive correlation.
  • WATANABE YASUNORI, TASHIRO KOKI, OTSUKA JUN'ICHI, OYAMA TAKAHIRO, YAMADA TOMOHITO
    土木学会論文集 B2(海岸工学)(Web) Japan Society of Civil Engineers 70 (2) I.56-I.60 (J-STAGE) - I_60 1883-8944 2014 [Not refereed][Not invited]
     
    High speed infrared imaging measurements were performed for identifying mechanical factors to govern surface skin temperatures on wind waves under moderate to strong winds. Surface renewals owing to turbulent disturbances are found to predominantly determine the skin temperature amplitude and phase lags to surface elevation, which is parameterized by a so-called wind-wave Reynolds number (RB). The modulations of the skin temperature variations are observed at RB ~ 4 × 104, indicating governing dynamics to produce surface turbulence is altered at the boundary.
  • UCHIYAMA YUSUKE, MATSUKAWA DAISUKE, KANKI RYOSUKE, BABA YASUYUKI, MORI NOBUHITO, MIZUTANI HIDEAKI, WATANABE YASUNORI, OTSUKA JUN'ICHI, YAMADA TOMOHITO, SARUWATARI AYUMI, NINOMIYA JUN'ICHI
    土木学会論文集 B2(海岸工学)(Web) Japan Society of Civil Engineers 70 (2) I.446-I.450 (J-STAGE) - I_450 1883-8944 2014 [Not refereed][Not invited]
     
    Tanabe bay is a small embayment connected directly to the Pacific Ocean to the south, whereas frequently suffers from harmful algal blooms due to sewage effluent and the local aquaculture industry. For preserving the ecosystem in the bay, it is necessary to understand an oceanic structure in the bay along with water exchange at the bay entrance. We thus conduct a comprehensive investigation consisting of a shipboard measurement, a season-long platform observation, and a triply nested high-resolution ocean modeling. The water exchange at the bay mouth is largely affected by semi-diurnal tidal currents and episodic subtidal intrusion of the offshore water controlled by mesoscale circulations.
  • Yamada Tomohito J, Farukh Murad. A, Fukushima Taiki, Inatsu Masaru, Sato Tomonori, Pokhrel Yadu N, Oki Taikan
    Hydrological Research Letters THE JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES 8 (4) 108 - 113 1882-3416 2014 [Not refereed][Not invited]
     
    This paper introduces a method named "hybrid-downscaling" to estimate the future extreme hourly precipitation intensity based on observational evidence of the 99th percentile precipitation intensity against air temperature in Sapporo and Tokyo, Japan. The future projected air temperature under the Special Report on Emissions Scenarios (SRES) A1B was used after dynamical downscaling using 3 different regional atmospheric models (RAMs) with lateral boundary conditions from 3 different general circulation models (GCMs). We analyzed the 99th percentile of hourly precipitation intensity against daily mean air temperature in Sapporo and Tokyo. The 99th percentile precipitation intensity tended to have an approximate equation in which the rate of increment was similar to the Clausius-Clapeyron rate of change in the saturated water vapor. This study also showed that the precipitable water vapor and the convective instability followed the Clausius-Clapeyron-like rate of change during the hours with the 99th percentile precipitation intensity.
  • Dwi Prabowo Yuga Suseno, Tomohito J. Yamada
    Journal of Hydrometeorology 14 (6) 1922 - 1932 1525-755X 2013/12 [Not refereed][Not invited]
     
    A rainfall estimation method was developed based on the statistical relationships between cloud-top temperature and rainfall rates acquired by both the 10.8-μm channel of the Multi-Functional Transport Satellite (MTSAT) series and the Automated Meteorological Data Acquisition System (AMeDAS) C-band radar, respectively. The method focused on cumulonimbus (Cb) clouds and was developed in the period of June-September 2010 and 2011 over the landmass of Japan and its surrounding area. Total precipitable water vapor (PWV) and atmospheric vertical instability were considered to represent the atmospheric environmental conditions during the development of statistical models. Validations were performed by comparing the estimated values with the observed rainfall derived from the AMeDAS rain gauge network and the Tropical Rainfall Measuring Mission (TRMM) 3B42 rainfall estimation product. The results demonstrated that the models that considered the combination of total PWV and atmospheric vertical instability were relatively more sensitive to heavy rainfall than were the models that considered no atmospheric environmental conditions. The use of such combined information indicated a reasonable improvement, especially in terms of the correlation between estimated and observed rainfall. Intercomparison results with the TRMM 3B42 confirmed that MTSAT-based rainfall estimations made by considering atmospheric environmental conditions were more accurate for estimating rainfall generated by Cb cloud. © 2013 American Meteorological Society.
  • KONO TAKENORI, KONO TAKENORI, YAMADA TOMOHITO, POKHREL YADU NATH
    地球環境研究論文集 Japan Society of Civil Engineers 21 (5) I.177-I.182 - I_182 2185-6648 2013/09/17 [Not refereed][Not invited]
     
    Water is a fundamental resource for human sustenance. However, the amount of water that is easily accessible is limited and therefore proper management of water resources is very important to fulfill the increasing demand and hence to maintain the standard of living for the escalating population. Recent studies have shown that human activities such as irrigation and reservoir operation have significantly affected the natural flow systems, and therefore accounting these human factors in the model is critically important to simulated land surface hydrologic processes realistically. Recently an integrated model "MATSIRO with human impacts" was developed by incorporating the human factors into the MATSIRO model. In this study, the global model was applied for Japan with a particular focus on Hokkaido region because Hokkaido is the largest agricultural region in Japan and agriculture accounts for the largest portion of human water use. Using the model, we show how the simulated hydrologic variables such as evapotranspiration and soil temperature are affected due to irrigation.
  • Tadashi Yamada, Tomohito J. Yamada, Syota Sasaki
    PROCEEDINGS OF THE 35TH IAHR WORLD CONGRESS, VOLS I AND II 356 - 368 2013 [Refereed][Not invited]
     
    The present study provides a readily understandable kinematic-based model to estimate the effective dose of radioactive substances in the human body without the need for consideration of any complicated mechanism. For example, the International Commission on Radiological Protection has developed an exact model, which is considered by radiologists the standard method of calculating the effective dose. However, this method is too complex for non-professional researchers of radiology to understand because it divides a human body into similar to 20 organs. In contrast, here we calculate the effective dose by regarding the human body as a single vessel. Although the present study does not involve consideration of a complicated mechanism, it does provide results with an accuracy equal to those of existing research.
  • Pokhrel Yadu N, Hanasaki Naota, Yeh Pat J. -F, Yamada Tomohito J, Kanae Shinjiro, Oki Taikan
    NATURE GEOSCIENCE 6 (1) 2 - 3 1752-0894 2013/01 [Refereed][Not invited]
  • FUKUSHIMA TAIKI, YAMADA TOMOHITO, MIYAZAKI SHIN
    土木学会論文集 B1(水工学)(Web) Japan Society of Civil Engineers 69 (4) I.1759-I.1764 (J-STAGE) - I_1764 2185-467X 2013 [Not refereed][Not invited]
     
    This paper discussed the land and sea breeze circulation (LSBC)between Ishikari and Yuhutsu areas in Hokkaido. The diurnal variation of LSBC during boreal summer(July and August) of 1985-2009 was mainly investigated by using various data. LSBC was observed between Ishikari and Sapporo up to 13km from coastal zones of the Japan Sea. Tomakomai to Atsuma area also showed LSBC around16km from coastal zones of the Pacific Ocean. For inland region that area from Chitose to Naganuma, southerly wind was observed all day long. The reason is related to a fact that this inland region has strong southerly wind associated with the meridional temperature gradient between Ishikari and Yuhutsu area. Thermal balance between SST and temperature of land could be important to control the horizontal scale of LSBC. In the La-Nina years, SST over the Japan Sea at the vicinity of Sapporo area was higher than the climatology, and LSBC was enhanced and expanded its spatial scale.
  • YAMADA Tomohito, HATA Yoshihiro
    PROCEEDINGS OF THE JAPANESE CONFERENCE ON HYDRAULICS Japan Society of Civil Engineers 69 (4) I_397 - I_402 2185-467X 2013 [Not refereed][Not invited]
     
    Atmospheric blocking is one of the main causes of extreme meteorological events such as spells of extremely cold weather, heat wave and continuous heavy rainfall in the mid-latitudes. The European Centre for Medium-Range Weather Forecasts Reanalysis Dataset (ERA-40) was analyzed to clarify both the characteristics of the latitudinal surface temperature field and the frequency of atmospheric blocking (FAB) in December, January, and February between 1960 and 1999. In years with a small meridional surface temperature gradient between the low and high latitudes, the FAB was larger than the average for the 40-year climatology, as well as persisting for longer and having a longitudinally larger spatial scale. A noticeable characteristic of these years was a larger dominant eddy scale length at the 500-hPa level compared to the average for the climatology. The amplitude of the dominant eddy scale length was also enhanced.
  • NAITO KENSUKE, IZUMI NORIHIRO, YOKOKAWA MIWA, YAMADA TOMOHITO
    土木学会論文集 B1(水工学)(Web) Japan Society of Civil Engineers 69 (4) I.1123-I.1128 (J-STAGE) - I_1128 2185-467X 2013 [Not refereed][Not invited]
     
    In recent years, cyclic steps are discovered in a variety of environments, such as deep ocean floors and ice floors on planets other than the earth. Water can exists only in the form of ice in the extraterrestrial environments, where temperature is commonly by far lower than that on the earth. Therefore, cyclic steps in the extraterrestrial environments are expected to be often found on ice. In order to obtain basic knowledge on the formation of ice steps, we have performed a series of experiments in a cold room of Institute of Low Temperature Science, Hokkaido University, and reproduced ice steps migrating in the downstream direction. In this paper, we formulated the formation process of ice steps, and provide a reasonable explanation of the downstream migrating ice steps based on the experimental results.
  • WATANABE YAMATO, YAMADA TOMOHITO, SUSENO DWI, PRABOWO YUGA
    土木学会論文集 B1(水工学)(Web) Japan Society of Civil Engineers 69 (4) I.301-I.306 (J-STAGE) - I_306 2185-467X 2013 [Not refereed][Not invited]
     
    There are many extreme hydrometeorological phenomena such as heavy rain and drought events in the world. A considerable shortage of observing stations was motivated us to utilize the remote sensing for observing water resources and related information from space. In this study we used MTSAT (Multi-functional Transport Satellite) to acquire cloud type characteristics. The observation target was the western pacific region. The spatial distribution between MTSAT and JMA(Japan Meteorological Agency) cloud classification showed reasonably good agreement while our result estimated many Cb(Cumulonimbus) focusing on June to September 2010. The Cb cloud was estimated 20 to 60% larger than the 15-year climatology(1996-2010) over northern part of Thailand in 2011.
  • YAMAHARA KOKI, YAMADA TOMOHITO, POKHREL YADU
    土木学会論文集 B1(水工学)(Web) Japan Society of Civil Engineers 69 (4) I.1807-I.1812 (J-STAGE) - I_1812 2185-467X 2013 [Not refereed][Not invited]
     
    In recent years, the damage caused by extreme weather events has frequently been reported in many parts of the world. Therefore the improvement of prediction accuracy for extreme events is an urgent issue. This study conducted to evaluate the sub-seasonal forecast skill with land initializations in an Atmospheric General Circulation Model (AGCM) targeting a severe drought event which occurred in the North American continental in boreal summer of 1988. The experiment using land initialization with influence of human activities, sub-seasonal forecast skill for near surface temperature improved its skill comparing with another forecast experiment without realistic land initializations. We obtained the result of forecast that soil moisture states could come to have a long dry state by considering human activities at the drought event.
  • Tomohito J. Yamada, Shinjiro Kanae, Taikan Oki, Randal D. Koster
    Hydrological Sciences Journal 58 (6) 1276 - 1286 0262-6667 2013 [Not refereed][Not invited]
     
    The seasonal variation of land-atmosphere coupling strength has been examined using an extended series of atmospheric general circulation model (AGCM) simulations. In the Western Sahel of Africa, strong coupling strength for precipitation is found in April and May, just prior to and at the beginning of the monsoon season. At this time, heat and water fluxes from the surface are strongly controlled by land conditions, and the unstable conditions in the lower level of the troposphere, as induced by local land state, allow the surface fluxes to influence the variability of convective precipitation-and thus the timing of monsoon onset.Editor Z. W. KundzewiczCitation Yamada, T.J., Kanae, S., Oki, T., and Koster, R.D., 2013. Seasonal variation of land-atmosphere coupling strength over the West African monsoon region in an atmospheric general circulation model. Hydrological Sciences Journal, 58 (6), 1276-1286. © 2013 IAHS Press.
  • KITANO YOSHIKAZU, YAMADA TOMOHITO, IZUMI NORIHIRO
    地球環境研究論文集 Japan Society of Civil Engineers 20 (5) I.205-I.210 - I_210 2185-6648 2012/09/13 [Not refereed][Not invited]
     
    There are many unknown issues about line-shaped rainbands (LRBs) which is one of the meso-scale meteorological phenomena making torrential rainfall events in Japan. For disaster prevention, it is very important to reveal the formation mechanism of LRBs. In order to know the mechanism, the authors try to examine the instability of the density stratification. In this study, the rainfall and thermodynamic effects are not considered. To simplify the discussion, this theory considers only the up/down motion of the disturbance in the stratified atmosphere. Using this theory, the authors correlate the region of horizontal disturbance and the two parameters which characterize the shape of LRBs, i.e. the Froude number and the rate of density difference.
  • Tomohito J. Yamada, Myong-In Lee, Masao Kanamitsu, Hideki Kanamaru
    JOURNAL OF HYDROMETEOROLOGY 13 (3) 1142 - 1148 1525-755X 2012/06 [Not refereed][Not invited]
     
    The diurnal characteristics of summer rainfall in the contiguous United States and northern Mexico were examined with the United States reanalysis for 5 years in 10-km horizontal resolution (US10), which is dynamically downscaled from the National Centers for Environmental Prediction National Center for Atmospheric Research (NCEP-NCAR) Global Reanalysis 1 using the Regional Spectral Model (RSM). The hourly precipitation outputs demonstrate a realistic structure in the temporal evolution of the observed rainfall episodes and their magnitudes across the United States without any prescriptions of the observed rainfall to the global reanalysis and the downscaled regional reanalysis. Nighttime rainfall over the Great Plains associated with eastward-propagating, mesoscale convective systems originating from the Rocky Mountains is also represented realistically in US 10, while the original reanalysis and most general circulation models (GCMs) have difficulties in capturing the series of nocturnal precipitation events in summer over the Plains. The results suggest an important role of the horizontal resolution of the model in resolving small-scale, propagating convective systems to improve the diurnal cycle of summer rainfall.
  • T. J. Yamada, S. Kanae, T. Oki, Y. Hirabayashi
    ATMOSPHERIC SCIENCE LETTERS 13 (2) 103 - 107 1530-261X 2012/04 [Refereed][Not invited]
     
    The simulation of the onset of the West African monsoon (WAM), associated with the northward shift of the Intertropical Convergence Zone (ITCZ) occurring in May, June, and July, is a challenging task for atmospheric general circulation models (AGCMs), because of complex water and energy balance through the land-atmosphere interaction as well as atmospheric processes. We provide evidence that a combination of state-of-the-art global fields of reanalyzed soil moisture anomalies and a sufficiently high-resolution (similar to 50 km) AGCM produces a successful simulation of the northward shift of the ITCZ and the following onset of the WAM in July. Copyright (C) 2011 Royal Meteorological Society
  • Tomohito J. Yamada, Jun Sasaki, Naoki Matsuoka
    ATMOSPHERIC SCIENCE LETTERS 13 (2) 133 - 138 1530-261X 2012/04 [Refereed][Not invited]
     
    Line-shaped rainbands (LRBs) are severe storm events that cause torrential rainfall across the mid-latitudes and are difficult to accurately predict because of their complex physical processes. We examined the occurrence of LRBs in boreal summer in northern Japan over the period 1990-2010. In years with anomalously many LRBs, the development of LRBs over northern Japan was driven by a combined positive anomaly of warm sea-surface temperatures and westerly moisture flux associated with the prominent pattern of the surface pressure anomalies between the main island of Japan and the Sea of Okhotsk. In contrast, the number of LRBs were significantly small with opposite characteristics. Copyright (C) 2012 Royal Meteorological Society
  • Yasunori Watanabe, Yuta Mitobe, Ayumi Saruwatari, Tomohito Yamada, Yasuo Niida
    Coastal Engineering Journal 54 (1) 2166-4250 2012/03 [Refereed][Not invited]
     
    A numerical computation of the 2011 Tohoku earthquake tsunami was performed to identify fundamental features of the tsunami evolution along the coast of Hokkaido, Japan. Edge waves formed at multiple locations where the refracted tsunami focused, governing local surface oscillations and regional variations in tsunami height along the Pacific coast of Hokkaido. The computation reasonably reproduced the distribution of surveyed tsunami height as well as the time records of surface elevation recorded at ports in Hokkaido. The major features of the frequency spectrum for the 2011 Tohoku tsunami were identical to those for the 2003 Tokachi-oki earthquake tsunami; inherent local properties of surface oscillation caused by the passage of edge waves existed, determined by the local bathymetry. © 2012 World Scientific Publishing Company and Japan Society of Civil Engineers.
  • Yasunori Watanabe, Yuta Mitobe, Ayumi Saruwatari, Tomohito Yamada, Yasuo Niida
    COASTAL ENGINEERING JOURNAL 54 (1) 1250002.1-1250002.17  0578-5634 2012/03 [Not refereed][Not invited]
     
    A numerical computation of the 2011 Tohoku earthquake tsunami was performed to identify fundamental features of the tsunami evolution along the coast of Hokkaido, Japan. Edge waves formed at multiple locations where the refracted tsunami focused, governing local surface oscillations and regional variations in tsunami height along the Pacific coast of Hokkaido. The computation reasonably reproduced the distribution of surveyed tsunami height as well as the time records of surface elevation recorded at ports in Hokkaido. The major features of the frequency spectrum for the 2011 Tohoku tsunami were identical to those for the 2003 Tokachi-oki earthquake tsunami; inherent local properties of surface oscillation caused by the passage of edge waves existed, determined by the local bathymetry.
  • WADA TAKUYA, YAMADA TOMOHITO, SUSENO YUGA DWI PRABOWO
    水工学論文集(CD-ROM) Japan Society of Civil Engineers 56 (4) ROMBUNNO.67 - I_402 1880-8751 2012/02/20 [Not refereed][Not invited]
     
    Meteorological characteristics of the formation and environment of the Niigata-Fukushima heavy rainfall on 28~30 July 2011 were studied. Line-shaped rainfall systems were observed by using synthetic radar and Xband MP radar on 29 July at 09~17 and on 30 July at 00~04. The purpose of this study is to classify these events and to reveal the reason why these occur and stagnate. It was found that the former event can be classified as Back Building type while the latter can be classified as Back Building composite type. The development environments were focused by the convergence, relative humidity, wind and temperature by using the Japan Meteorological Agency GPV mesoscale model dataset. Results indicate that convergence area, flow of high-humidity air at 950hpa and incursion of dry-low-temperature air generated the event on 29 July at 09~17. The event on 30 July at 00~04 was generated by the effect of cold air at 400hpa which flowed into high-humidity region.
  • SUSENO Dwi, Prabowo Yuga, YAMADA Tomohito J
    PROCEEDINGS OF THE JAPANESE CONFERENCE ON HYDRAULICS Japan Society of Civil Engineers 68 (4) I_175 - I_180 2185-467X 2012 [Not refereed][Not invited]
     
    This research deals with the use of geostationary satellite based rainfall estimation for characterizing storm severity. The objectives of this research are to estimate storm rainfall intensity by using Multi-functional Transport Satellite (MTSAT) blended with C-band rainfall radar data and to show the severity of the identified storm rainfall intensity by representing its return period map. A regional frequency analysis (RFA) method developed by Hosking and Wallis (1997) is used to define the frequency distribution of long-term hourly maximum rainfall over Hokkaido Island. RFA indicates that Generalized Normal/Log Normal three parameters (GNO/LN3) is suitable to describe the frequency distribution of long-term hourly maximum rainfall over Hokkaido Island. Characterization of severity of 24 August 2010 storm event has been performed over Ishikari river basin, Hokkaido according to estimated rainfall using MTSAT data. Even though the return period map shows underestimation in comparison with the current situation of flood event in Ishikari river basin, this information is useful for flood control and mitigation.
  • Dwi Prabowo Yuga Suseno, Tomohito J. Yamada
    REMOTE SENSING LETTERS 3 (8) 737 - 746 2150-704X 2012 [Not refereed][Not invited]
     
    A new two-dimensional threshold diagram (2D-THR) has been developed based on maximum likelihood cloud classification results, which can readily be applied for Multi-functional Transport Satellite (MTSAT) split window datasets. Because 2D-THR was trained using northern summer 2010 data for Japan and its surrounding area, it is typically suitable only for summer. Comparison of snapshot cloud type distributions showed that 2D-THR images and the corresponding night-time microphysical colour composite images as well as 2D-THR images and Japan Meteorological Agency (JMA) cloud type images are in good agreement. A time series inter-comparison of the hourly 2D-THR cloud classification results with the JMA cloud type classification data product was performed by calculating spatial correlation of cloud percentage for 1 degrees x 1 degrees grid cells. For cumulonimbus, high-level, middle-level and low-level clouds over tropical and subtropical areas in the northwestern Pacific Ocean region, the spatial correlation between 2D-THR and JMA is moderate. Thus, 2D-THR cloud classification algorithm can be applied in both regions.
  • Yasunori Watanabe, Yuta Mitobe, Yasuo Niida, Tomohito Yamada
    Proceedings of the International Offshore and Polar Engineering Conference 218 - 223 1098-6189 2011/09/19 [Not refereed][Not invited]
     
    Adaptive mesh refinement (AMR) is one of the powerful computational tools to enhance local computing resolution at less cost. In this paper, computational performances of AMR for tsunami computer simulations were examined in terms of the accuracy and computational cost through computational tests for long wave propagation initiated by collapse of a water column on still water. AMR was also applied to a practical tsunami evolution - 2003 Tokachi-oki earthquake tsunami, which was compared with observed water elevation for examining the applicability of this method to practical tsunami events. It was found through the numerical tests that the present method is capable of efficiently performing reliable computations of tsunami propagation at high resolution. Copyright © 2011 by the International Society of Offshore and Polar Engineers (ISOPE).
  • WADA TAKUYA, YAMADA TOMOHITO
    水工学論文集(CD-ROM) Japan Society of Civil Engineers 55 (4) ROMBUNNO.81 - I_486 1880-8751 2011/02/22 [Not refereed][Not invited]
     
    Various problems concerning the global environment such as climate change, urbanization, and the heat island phenomenon are paid to attention, especially in terms of rainfall characteristics. This paper focused on characteristics of diurnal patterns of rainfall at Tokyo (Ohtemachi) based on 120-years hourly data from 1890 to 2008. Diurnal patterns were analyzed by using the "P/D" diagnostics which indicates the shape of a single rainfall event by the peak rainfall amount and its duration (whole duration). The P/D diagnostics showed the intensification of short-time rainfall amount in recent. In addition, we proposed a new "P/D" diagnostics which indicates the shape of a single rainfall event with the peak rainfall amount and its duration (from the starting time to the peak time). The results we obtained are following. 1) There is an increasing tendency in the short-time afternoon rainfall. 2) The duration to reaching peak amount for each single rainfall event is clearly decreased particularly at 15LST and 19LST in the recent two decades.
  • Takuya WADA, Tomohito YAMADA
    Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering) 67 (4) I_481 - I_486 2011 [Refereed]
  • YAMADA TOMOHITO J, KOSTER RANDAL D, KANAE SHINJIRO, OKI TAIKAN
    水工学論文集(CD-ROM) 54 ROMBUNNO.56  1880-8751 2010/02/22 [Not refereed][Not invited]
  • aikawa makoto, Qian chaochao, igarashi gou, ichiki shintarou, yamada tadashi
    Proceeding of Annual Conference 水文・水資源学会 23 87 - 87 2010 
    河口部では，河川流，沿岸流，潮汐流，波浪など様々な流れが混在しており，非常に複雑な流れをしていることが一般的に知られている．これらの流れにより河口部の河床では，複雑な河床変動が生じており，河床の形成や発達の解明は困難である．よって本研究では沿岸流，潮汐流，波浪といった条件を除き河川流に着目した水理実験を行った．本実験は下流端水位や流量の条件を変化させ，河川流が河床の形成及び流速への影響を明らかにすることを目的とする．
  • Tomohito J. Yamada, Randal D. Koster, Shinjiro Kanae, Taikan Oki
    MONTHLY WEATHER REVIEW 135 (7) 2674 - 2687 0027-0644 2007/07 [Not refereed][Not invited]
     
    This study reveals the mathematical structure of a statistical index, Omega, that quantifies similarity among ensemble members in a weather forecast. Previous approaches for quantifying predictability estimate separately the phase and shape characteristics of a forecast ensemble. The diagnostic Omega, on the other hand, characterizes the similarity (across ensemble members) of both aspects together with a simple expression. The diagnostic Omega is thus more mathematically versatile than previous indices.
  • YAMADA TOMOHITO, KANAE SHINJIRO, OKI TAIKAN
    水工学論文集(CD-ROM) Japan Society of Civil Engineers 51 ROMBUNNO.53 - 318 1880-8751 2007/02/22 [Not refereed][Not invited]
     
    The predictability of the Indian summer monsoon is examined from an ensemble of 16 atmospheric general circulation model simulations with prescribed sea surface temperatures (SST). The predictability is estimated with a statistical index (Ω) to quantify similarity among the ensemble members. The model simulations show that the predictability of precipitation and the low-level moisture flux during May and June are much larger than that in July and August. The role of land-atmosphere interaction is also focused. During May and June the predictability of soil moisture and near surface temperature are increased by large predictability of precipitation. At the same time, the predictability of cumulus type precipitation could be improved or maintained by positive feedback of large predictability of soil moisture and near surface temperature through atmospheric instability in atmospheric boundary layer. Finally, we suggest two new statistical methods to estimate the phase and shape predictability, and discuss the monthly change of the predictability of the Indian summer monsoon using 3 types of predictability including Ω.
  • Zhichang Guo, Paul A. Dirmeyer, Randal D. Koster, Gordon Bonan, Edmond Chan, Peter Cox, C. T. Gordon, Shinjiro Kanae, Eva Kowalczyk, David Lawrence, Ping Liu, Cheng-Hsuan Lu, Sergey Malyshev, Bryant McAvaney, J. L. McGregor, Ken Mitchell, David Mocko, Taikan Oki, Keith W. Oleson, Andrew Pitman, Y. C. Sud, Christopher M. Taylor, Diana Verseghy, Ratko Vasic, Yongkang Xue, Tomohito Yamada
    JOURNAL OF HYDROMETEOROLOGY 7 (4) 611 - 625 1525-755X 2006/08 [Not refereed][Not invited]
     
    The 12 weather and climate models participating in the Global Land-Atmosphere Coupling Experiment ( GLACE) show both a wide variation in the strength of land-atmosphere coupling and some intriguing commonalities. In this paper, the causes of variations in coupling strength-both the geographic variations within a given model and the model-to-model differences-are addressed. The ability of soil moisture to affect precipitation is examined in two stages, namely, the ability of the soil moisture to affect evaporation, and the ability of evaporation to affect precipitation. Most of the differences between the models and within a given model are found to be associated with the first stage-an evaporation rate that varies strongly and consistently with soil moisture tends to lead to a higher coupling strength. The first-stage differences reflect identifiable differences in model parameterization and model climate. Intermodel differences in the evaporation-precipitation connection, however, also play a key role.
  • Randal D. Koster, Zhichang Guo, Paul A. Dirmeyer, Gordon Bonan, Edmond Chan, Peter Cox, Harvey Davies, C. T. Gordon, Shinjiro Kanae, Eva Kowalczyk, David Lawrence, Ping Liu, Cheng-Hsuan Lu, Sergey Malyshev, Bryant McAvaney, Ken Mitchell, David Mocko, Taikan Oki, Keith W. Oleson, Andrew Pitman, Y. C. Sud, Christopher M. Taylor, Diana Verseghy, Ratko Vasic, Yongkang Xue, Tomohito Yamada
    JOURNAL OF HYDROMETEOROLOGY 7 (4) 590 - 610 1525-755X 2006/08 [Not refereed][Not invited]
     
    The Global Land-Atmosphere Coupling Experiment ( GLACE) is a model intercomparison study focusing on a typically neglected yet critical element of numerical weather and climate modeling: land atmosphere coupling strength, or the degree to which anomalies in land surface state ( e. g., soil moisture) can affect rainfall generation and other atmospheric processes. The 12 AGCM groups participating in GLACE performed a series of simple numerical experiments that allow the objective quantification of this element for boreal summer. The derived coupling strengths vary widely. Some similarity, however, is found in the spatial patterns generated by the models, with enough similarity to pinpoint multimodel "hot spots" of land-atmosphere coupling. For boreal summer, such hot spots for precipitation and temperature are found over large regions of Africa, central North America, and India; a hot spot for temperature is also found over eastern China. The design of the GLACE simulations are described in full detail so that any interested modeling group can repeat them easily and thereby place their model's coupling strength within the broad range of those documented here.
  • Hasegawa, K, T.Araya, T. Ogawa, S. Kikuchi, M. Kuroki, T. Komatsu, H. Saga, Y. Shimizu, O. Shimizu, H. Suzuki, Y. Suzuki, G. Tanaka, S. Tohma, M. Nakatsugawa, S. Hatta, Y. Murakami, T. Yamashita, T. Yamada, Y. Watanabe, Y. Watanabe, M. Fujita
    Journal of Hydroscience and Hydraulic Engineering 24 (1) 41 - 56 0912-2508 2006/05 [Refereed][Not invited]
  • S Kanae, Y Hirabayashi, T Yamada, T Oki
    JOURNAL OF CLIMATE 19 (8) 1450 - 1460 0894-8755 2006/04 [Not refereed][Not invited]
     
    Outputs from two ensembles of atmospheric model simulations for 1951-98 define the influence of "realistic" land surface wetness on seasonal precipitation predictability in boreal summer. The ensembles consist of one forced with observed sea surface temperatures (SSTs) and the other forced with realistic land surface wetness as well as SSTs. Predictability was determined from correlations between the time series of simulated and observed precipitation. The ratio of forced variance to total variance determined potential predictability. Predictability occurred over some land areas adjacent to tropical oceans without land wetness forcing. On the other hand, because of the chaotic nature of the atmosphere, considerable parts of the land areas of the globe did not even show potential predictability with both land wetness and SST forcings. The use of land wetness forcing enhanced predictability over semiarid regions. Such semiarid regions are generally characterized by a negative correlation between fluxes of latent heat and sensible heat from the land surface, and are "water-regulating" areas where soil moisture plays a governing role in land-atmosphere interactions. Actual seasonal prediction may be possible in these regions if slowly varying surface conditions can be estimated in advance. In contrast, some land regions (e.g., south of the Sahel, the Amazon, and Indochina) showed little predictability despite high potential predictability. These regions are mostly characterized by a positive correlation between the surface fluxes, and are "radiation-regulating" areas where the atmosphere plays a leading role. Improvements in predictability for these regions may require further improvements in model physics.
  • YAMADA TOMOHITO, KANAE SHINJIRO, OKI TAIKAN
    水工学論文集 Japan Society of Civil Engineers 49 (1) 1 - 6 0916-7374 2005/02/01 [Not refereed][Not invited]
     
    It is shown that a similarity parameter has new mathematical structure. Heretofore, the correlation coefficient is used for quantifying the correlation relationship between two ensemble members. Koster et al<SUP>1</SUP> introduced a statistical parameter, called Ω to quantify the similarity among several ensemble members with calculating the ensemble numbers and the two types of variances. However the mathematical structure of Ω had not been revealed in their studies. The present authors applied to derivate Ω for understanding the mathematical meaning of it. As results, we could have a knowledge that Ω consists of mainly two terms. One is the average value of cross correlation coefficients (ACCC) across all ensemble members. Another is the similarity of the mean value and the variance across all ensemble members. Therfore, the authorscan conclude that Ω shows the similarity of the 'shape' of all ensemble members and the mathematical characteristics is more capacious than the correlation coefficient. The paper ends with some remarks on the mathematical characteristics of 'as a new evaluation methodology for the predictabity of numerical forecast.' in monthly or seasonal time scale.
  • RD Koster, PA Dirmeyer, ZC Guo, G Bonan, E Chan, P Cox, CT Gordon, S Kanae, E Kowalczyk, D Lawrence, P Liu, CH Lu, S Malyshev, B McAvaney, K Mitchell, D Mocko, T Oki, K Oleson, A Pitman, YC Sud, CM Taylor, D Verseghy, R Vasic, YK Xue, T Yamada
    SCIENCE 305 (5687) 1138 - 1140 0036-8075 2004/08 [Refereed][Not invited]
     
    Previous estimates of land-atmosphere interaction (the impact of soil moisture on precipitation) have been limited by a lack of observational data and by the model dependence of computational estimates. To counter the second limitation, a dozen climate-modeling groups have recently performed the same highly controlled numerical experiment as part of a coordinated comparison project. This allows a multimodel estimation of the regions on Earth where precipitation is affected by soil moisture anomalies during Northern Hemisphere summer. Potential bene its of this estimation may include improved seasonal rainfall forecasts.
  • YAMADA TOMOHITO, KANAE SHINJIRO, OKI TAIKAN
    水工学論文集 Japan Society of Civil Engineers 48 (1) 223 - 228 0916-7374 2004/02/01 [Not refereed][Not invited]
     
    The extent of the coupling strength between the land and the atmosphere controls the behavior of the atmospheric processes. Precipitation is induced by the soil moisture variation. K02 focused on the coupling strength between four AGCMs. It is mentioned that the coupling strength has much model dependence. The authors are participating the GLACE (Global Land-Atmosphere Coupling Experiment) which follows the K02 experiment. Before undertaking the GLACE experiment, it is conducted the K02 experiment to compare or evaluate our AGCM (CCSR/NIES) result with K02 results. As a result, the coupling strength on the precipitation process is much weaker than the latent heat flux. This is the same characteristics in three of four models in other K02 participants. Moreover, the coupling strength on the latent heat flux shows the relatively high value over the Central Eurasia or the North America.

Books etc

  • 水文・水資源学会誌 Vol.35, No.2
    山田朋人 (私にとっての発想のたまご)
    水文・水資源学会 2022/03
  • ながれ
    一般社団法人日本流体力学会 (気候変動を踏まえた豪雨・洪水氾濫リスクの考え方)
    2021
  • 総合土木技術誌土木施工
    オフィス・スペース (気候変動下における大雨の将来リスクに関する新しい解釈と提案)
    2021
  • 雑誌「河川」
    日本河川協会 (アンサンブル手法による気候変動予測・リスク評価の考え方)
    2020
  • 気候変動適応技術の社会実装ガイドブック
    SI-CATガイドブック編集委員会 (Contributor)
    技報堂出版 2020
  • 国土交通省北海道開発局，北海道，北海道大学 監修：気候変動を踏まえた新しい洪水リスク解析
    一般財団法人 北海道河川財団 (Supervisor)
    2019
  • 水循環 Journal of hydrological system :貯留と浸透
    雨水貯留浸透技術協会 (気候変動下における積雪寒冷地域で想定される水循環，水資源の特徴)
    2019
  • 水理公式集 [2018年度版]
    土木学会 水工学委員会 (Contributor第2章 気象と大気・陸面水文過程)
    2019
  • 生活と環境
    日本環境衛生センター (将来の短時間豪雨の推定と降雨の不確実性―北海道を対象とする総合的ダウンスケール手法の開発と適用)
    2015
  • Designing Climate Change Adaptation
    三村 信男, 太田 俊二, 武若 聡, 亀井 雅敏 (Contributor)
    株式会社クロスメディア・マーケティング 2015

MISC

Awards & Honors

  • 2023/05 令和四年度土木学会北海道支部技術研究発表会 土木学会北海道支部優秀学生講演賞
     石狩川の感潮区域における大気の影響を踏まえた海水と淡水の相互作用 
    受賞者: 田中健人,山田朋人
  • 2023/05 令和四年度土木学会北海道支部技術研究発表会 土木学会北海道支部優秀学生講演賞
     2007年台風9号と2019年台風19号が利根川・千曲川両流域を通過した際における地形性降雨の発生条件 
    受賞者: 松岡陽生,山田朋人
  • 2022/10 水文・水資源学会／日本水文科学会 2022年度研究発表会 優秀発表賞
     夏季の北海道とその周辺域における豪雨の抽出とその時空間特性 
    受賞者: 大屋祐太;山田朋人
  • 2022/10 水文・水資源学会/日本水文科学会 水文・水資源学会/日本水文科学会2022年度研究発表会における優秀発表賞
     夏季の北海道とその周辺域における豪雨の抽出とその時空間特性 
    受賞者: 大屋祐太;山田朋人
  • 2022/09 第30回地球環境シンポジウム 地球環境優秀講演賞
     気候予測データに基づく災害シナリオ作成 ～自治体災害支援システムIDR4Mを活用した避難情報の発令判断支援に向けて～ 
    受賞者: 植村郁彦,鈴⽊章弘,⽯原道秀,⽶⽥駿星,星野剛,⼭本太郎,⼭⽥朋⼈
  • 2022/09 第30回地球環境シンポジウム 地球環境シンポジウム優秀ポスター賞
     気候予測データベースを活用した自治体の避難判断支援のための防災研修 
    受賞者: 鈴木章弘;植村郁彦;星野剛;米田駿星;山本太郎;橋本慎一;山田朋人
  • 2022/09 土木学会 ポスター発表賞
     気候予測データベースを活用した自治体の避難判断支援のための防災研修 
    受賞者: 鈴木章弘;植村郁彦;星野剛;米田駿星;山本太郎;橋本慎一;山田朋人
  • 2022/08 第30回地球環境シンポジウム 地球環境優秀講演賞
     内外水同時解析を用いた浸水特性の分析 
    受賞者: 米田駿星;佐藤誠;江口陽祐;山田朋人
  • 2021/07 日本気象学会北海道支部 北海道支部発表賞
     北海道周辺域で線状降水帯が発生しやすい準季節平均場の将来変化 
    受賞者: 大屋 祐太;山田朋人
  • 2021/06 2020年度河川技術論文賞
     気候変動予測情報を用いた極値水文量の統計的推定 
    受賞者: 清水啓太,山田正,山田朋人
  • 2021/05 土木学会北海道支部 令和二年度土木学会北海道支部優秀学生講演賞
     降雨流出現象の不確実性に関する研究 
    受賞者: 青木一眞;山田朋人;成岱蔚
  • 2021/05 土木学会北海道支部 令和二年度土木学会北海道支部優秀学生講演賞
     気象要素を用いる客観手法による梅雨前線の季節進行と年々変動 
    受賞者: 宮本真希;山田朋人
  • 2021/05 土木学会北海道支部 令和二年度土木学会北海道支部優秀学生講演賞
     厚真川小流域における崩壊斜面からの流出土砂量の観測 
    受賞者: 宮崎功太郎;星野剛;山田朋人;橋場雅弘
  • 2019/05 土木学会北海道支部 平成30年度土木学会北海道支部優秀学生講演賞
     無次元数を用いた十勝川集水域における豪雨の地形依存性評価 
    受賞者: 竹原由;山田朋人
  • 2018/11 土木学会水工学委員会 平成30年度 土木学会水工学論文奨励賞
     確率限界法検定に基づく確率分布モデルの信頼区間を導入した新しい水文頻度解析手法 
    受賞者: 清水啓太;山田朋人;山田 正
  • 2018/06 2018年度河川技術に関するシンポジウム 2018年河川技術に関するシンポジウム優秀発表者賞
     北海道における気候変動に伴う洪水外力の変化 
    受賞者: 山田朋人
  • 2018 Japan Society of Civil Engineers 2018年度河川技術論文賞受賞
     北海道における気候変動に伴う洪水リスクの変化 
    受賞者: 山田朋人;星野剛;舛屋繁和;植村郁彦;吉田隆年;大村宣明;山本太郎;千葉学;戸村翔;時岡真治;佐々木博文;濱田悠貴;中津川誠
  • 2017/09 第25回地球環境シンポジウム 第25回地球環境シンポジウム優秀ポスター賞
     確率限界法検定に基づく確率水文量の信頼区間に関する研究 
    受賞者: 清水啓太,山田朋人,山田 正
  • 2016/12 土木学会応用力学委員会 応用力学シンポジウムポスター賞
     北西太平洋を通過する爆弾低気圧と台風の比較 
    受賞者: 北野慈和;山田朋人
  • 2016/09 土木学会地球環境委員会 平成28年度地球環境論文奨励賞
     底面の加熱および冷却を伴う回転水槽実験による傾圧不安定波の再現 
    受賞者: 一瀬輪子, 北野慈和, 山田朋人, 渡部靖憲, 泉典洋
  • 2016/01 土木学会北海道支部 第56回土木学会北海道支部優秀学生講演賞
     大陸スケールにおける消雪日の空間分布および年々特性 
    受賞者: 布川 敦士;山田 朋人
  • 2015/09 土木学会 平成27年度第23回地球環境シンポジウム優秀ポスター賞
     ディスドロメータを用いた飛沫粒径分布の風速及び高度依存性 
    受賞者: 岡地寛季;山田朋人;渡部靖憲;猿渡亜由未;大塚 淳一;馬場 康之;水谷 英朗;久保 輝広;二宮 順一;内山 雄介;森 信人
  • 2015/04 土木学会北海道支部 平成26年度優秀学生講演賞
     CMIP5マルチモデルにおけるブロッキング発生頻度と極端現象の変遷 
    受賞者: 北野慈和;山田朋人
  • 2014/04 土木学会北海道支部 平成25年度土木学会北海道支部優秀学生講演賞
     MTSAT近赤外放射情報を用いた夏季のチャオプラヤ川流域における雲の日内特性 
    受賞者: 渡部大和;山田朋人
  • 2013/04 土木学会北海道支部令和二年度年次技術研究発表会 平成23年度土木学会北海道支部優秀学生講演賞
     夏季における石狩〜苫小牧館の海陸風循環 
    受賞者: 福島大輝;山田朋人
  • 2013/04 土木学会北海道支部 土木学会北海道支部優秀学生講演賞
     密度界面に発生するship waveの物理機構 
    受賞者: 北野慈和;山田朋人;泉典洋

Research Grants & Projects

  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2023/04 -2028/03 
    Author : 秋山 充良, 山田 朋人, 本田 利器, 松崎 裕, 石橋 寛樹, 高橋 良和
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2022/04 -2025/03 
    Author : 山田 朋人, 中津川 誠, 星野 剛
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2019/12 -2023/03 
    Author : 二瓶 泰雄, 中北 英一, 竹見 哲也, 山田 朋人, 三隅 良平, 飯塚 聡, 鈴木 真一, 仲江川 敏之, 柳瀬 亘, 立川 康人, 田中 茂信, 佐山 敬洋, 田中 智大, 朝位 孝二, 前野 詩朗, 田中 仁, 吉谷 純一, 田中 規夫, 泉 典洋, 矢野 真一郎, 森脇 亮, 赤松 良久, 内田 龍彦, 重枝 未玲, 岩崎 理樹, 清水 義彦, 小山 毅, 長谷川 兼一, 西嶋 一欽, 藤本 郷史, 毛利 栄征, 前田 健一, 岡村 未対, 卜部 厚志, 森口 周二, 蝦名 裕一, 松四 雄騎, 王 功輝, 竹林 洋史, 鈴木 素之, 田島 芳満, 佐々木 淳, 信岡 尚道, 森 信人, 有川 太郎, 鈴木 崇之, 下園 武範, 松井 正宏, 小林 文明, 畑山 満則, 牛山 素行, 佐藤 健, 梶谷 義雄
     
    令和元年東日本台風（台風19号）とその2週間後の大雨（台風21号と低気圧）による広域災害の被害状況・メカニズムの全容を明らかにすることを目的とし，多角的・総合的に多くの分野の専門家からなる研究グループを結成し，調査研究を継続して行った．ここでは，①台風・低気圧による豪雨・流出現象の気象学的解明，②広域にわたる洪水氾濫災害を引き起こしたメカニズムの解明，③多発した土砂災害・土構造物破壊におけるメカニズムの解明，④強風や高潮による被害実態の解明，⑤住民の避難行動の実態と防災情報の伝達状況の把握，の5つのテーマと主に対象とした．その結果，台風19号による豪雨に，山岳部は勿論，平野部でもseeder-feeder機構が貢献していることを，XRAINによる立体観測情報，ひまわりによる観測情報により，seeder-feeder機構を表現した数値モデルを用いて示した．2019年台風19号による豪雨発生機構について，気象庁メソ客観解析データを用いて，降水活動に係る大気安定度や水蒸気場の解析をし，本豪雨発生時には，最近の他の豪雨事例と比較して，湿潤絶対不安定が持続して形成されていたことが分かった．また，洪水氾濫による建築被害に関しては，長野市内の水害被害住宅を対象に，復旧後の室内環境に着目して現地調査を実施している．復旧には数ヶ月の期間を要するが，復旧手順は現地の判断で実施している場合が多く，客観的な情報が整備されていない．その一助となるべく，限られた事例ではあるが，復旧手順とともにそれに伴う環境改善効果を評価しながら知見を蓄積し，環境改善を測るために室内の浮遊真菌濃度や部位の含水率等を計測した．さらに，風水害に関しては，台風に伴って発生した竜巻の影響が大きかったため，台風と竜巻発生の関係を過去の気象資料から抽出し整理した．
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2019/04 -2023/03 
    Author : 廣田 知良, 稲津 將, 山田 朋人, 西尾 善太, 小南 靖弘, 下田 星児, 村上 貴一, 臼井 靖浩, 横山 岳, 濱嵜 孝弘
     
    大規模アンサンブル気象データベースd4pdfを用いて北海道のバレイショへの温暖化への影響と適応策の検討し、温暖化によって収量が低下するリスクは増加し、また作期の早期化では対応できず、高温耐性を持つ品種への転換が重要な適応策になることが明らかとなった。北海道の十勝川水系などの解析から大規模アンサンブル気象データベースd4pdfを用いて洪水リスクの定量化が実現した。北海道胆振東部地震が農地侵食に与える影響について、震災後は大規模土砂崩壊リスクが高まっていると推定され、将来における極端降雨における侵食リスクと共に考慮すべきであることを示した。北海道における冬季の気候変動が農業に与える影響については、１）小麦における雪踏みによる野良イモ防除について現地実証で有効性を示し、２）地形情報および高層気象の情報を説明変数として取り入れた機械学習により、冬季の厳寒条件における気温の空間補間値を補正する手法を開発すると共に、３）融雪水の浸透効果を取り組んだモデル化と４）大規模アンサンブル気象データベースd4pdfを土壌凍結深推定手法と組み合わせて解析する手法開発に着手、５）北海道の小麦栽培における融雪促進影響を検討し、融雪材の促進効果は地域や融雪材散布後の気象条件で与える効果が異なることがわかった。データレスキューでは北海道や関東の小麦、北海道における圃場作業記録、北海道のワイン用ブドウ、九州の1958年～2019年の過去60年の気象概況と農作概況および農業気象災害のデータレスキューについて、これまで入手困難あるいは注目されてこなかったデータも含めて収集が進んだ。また、行政ルートからのデータ収集探査を詳細に集める手法を検討すると共に、テンサイについては、昭和30年代に国の農業研究機関を中心に進められた暖地テンサイに関する各種資料が温暖化研究に展開できる可能性を見出した。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2019/04 -2022/03 
    Author : Yamada Tomohito
     
    1)Based on a large amount of rainfall data, we classified the causes of extreme rainfall into thermodynamic and dynamic aspects, and it was also found that the increase in future rainfall in mountainous areas is related to dynamic aspect in addition to thermodynamic aspect. 2)We quantified the degree of freedom of extreme rainfall in the climate system, proposed a method for predicting future changes in stochastic rainfall. 3)Based on the relationship between total rainfall and rainfall within the flood arrival time and the combined occurrence probability of the two, we showed the existence of rainfall that causes high frequency and high inundation, which could not be understood by the probability evaluation of actual total rainfall. 4)We made it possible to discuss the efficient investment ratios for river management for main and tributary rivers, considering the uncertainty of the damage reduction effect of river management caused by the spatial distribution of rainfall.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2019/04 -2022/03 
    Author : YAMADA Yoshinori
     
    This study has elucidated many new features of convective clouds. Major findings are the clarification of the actual condition of convective clouds, the formation and maintenance mechanism of a line-shaped precipitation system by organization of cumulonimbus clouds, the occurrence mechanism of severe phenomena, and a development of novel approach of short-range forecast of 1-minute precipitation amount by an ensemble of an advanced three-dimensional wind synthesis over a complex terrain, high-resolution numerical model experiments, polarization radar analysis, and a non-linear time series analysis. In particular, it is notable that a success of the elucidation of the time evolution of three-dimensional structures of convective clouds at a very high temporal resolution of 30 seconds by employing dual-Doppler wind synthesis that uses two cutting-edge phased array weather radars. Many of these accomplishments are published in peer reviewed papers and in conference presentations.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2018/04 -2022/03 
    Author : Yasunori Watanabe
     
    We developed computational models to simulate turbulence transitions over waves, formations of thermal boundary layers, and bubble-mediated turbulent flows, which provides physical mechanims contributing to sea-surface drag forces and momentum transfers between atmosphere and ocean. In wind tunnel experiemnts, for the first, we succesfully measured size spectra of the both of sea spray dispersed in atmosphere and air bubbles entrained into sea owing to wind wave breaking, which is related to the sea surface drag and bulk parameters. Contributions of gas dissolution from the entrained bubbles to air-sea gas exchages have been identified through physical and computational experiments. A new model of bubble drag in bubble clouds was also developed in this project, contributing physical understanding of wave-induced aeration process. In ocean observation, features of sea spray, bubble entrainment due to wind wave breaking, and their contributions to heat transfers across sea surfaces.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2020/04 -2021/03 
    Author : YAMADA TADASHI
     
    The purpose of this research was to develop exploration technology by muons in order to visualize the internal structure of levees and civil engineering structures. The research is divided into four topics. As a result, we were able to establish a compact visualization technology which can measure in a short time. The present research has succeeded in downsizing the detector to the size of a laptop and can easily visualize soil cover with thickness up to about 3 m. In addition, when a visualization experiment of the levees was carried out using a simultaneously counting type muon detector, the levee shape could be caught in about 8 hours. Moreover, we also succeeded in visualizing the infiltration situation of a soil tank in an experiment, so it is possible to utilize it as a new technology that can visualize the internal situation of the levee at the time of flood.
  • Newly Development of Inner Visualization for River Levee and Engineering Structures by using Mu-Particle.
    Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Challenging Research (Pioneering)
    Date (from‐to) : 2018/06 -2021/03 
    Author : 山田 正, 安田 浩保, 山田 朋人, 森島 邦博, 平川 大貴, 前田 健一
     
    近年の極端降水現象により甚大な河川災害が繰り返されている。河川災害は、越流破堤と浸透破堤が二大要因であり、この現象を解明するためには、河川堤防の幾何形状と内部状態を空間的に連続して把握することが求められるが、既存の計測技術では不可能である。これに対し、近年注目されている宇宙線ミュー粒子を活用した探査技術を導入し、半導体技術を用いることで継続時間の大幅な短縮と形状の自由度を達成できる新たな可視化技術の確立を目的としている。 今年度は本研究において研究課題として設定した①～④のうち、①と②について実施する予定であったが、③についても取り組むことができた。 研究課題①ミュー粒子による検出器の計測対象の検討：計測対象を検討するために、水文学と地盤工学の土木工学の研究者と宇宙線を専門とする物理学者で定期的に会合を持ち、ミュー粒子検出器により初めて実像の把握が見込める土木構造物にどのようなものがあるのか議論した。その結果，検出器での検出結果と実像の実態を比較検証できる構造物であることが必須要件であるという結論になり、まずは試験体としての土層を製作し、その形状や浸水条件等を変更させながら試験計測を行うことになった。 研究課題②既存の同時計測型の検出器による試験計測：現場での試験計測を行うに当たっての基礎情報を入手するため、複数の河川において現地踏査を行い、現状の確認を行った。また、地下鉄道の漏水箇所を特定できる可能性についても試験計測を行った。 研究課題③光半導体型のミュー粒子検出器の設計と試作：基礎研究として、河川堤防の内部状態を把握するために必要な分解能と、その分解能を実現するために必要なミュー粒子数を捕捉する計測所要時間を概算するための数値計算を行った。これらの計算結果をもとに、光半導体型検出器の設計を行った。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2017/07 -2020/03 
    Author : Yasunari Teppei J.
     
    We carried out researches on “hazards”, “food resources”, “water resources”, and “air pollutions”, using climate models, satellite data, and reanalysis data together with some economic analyses, which are relevant to human sustainability in the future,. In terms of “air pollutions”, we found the climate and environmental factors related to large-scale wildfire occurrences, and further performed machine learning for its prediction as a preliminary research. The global simulations under the increased Siberian wildfire conditions by a climate model, MIROC/SPRINTARS, revealed that the number of days exceeding the environmental standard of PM2.5 in Japan, increased premature mortality, and its economic impact. The updated crop growth model, MATCRO, was incorporated to the latest MIROC. Another climate model simulation also revealed that the frequency of unprecedented occurrences on the observed precipitation was well explained with the temperature trend of 0.5 K per 100 years.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2017/06 -2020/03 
    Author : Fujita Mikiko
     
    The measuring of water vapor amount is essential for the understanding of the convective system that causes heavy precipitation. Especially for the heavy precipitation that occurs in the boreal summer around Japan, it's desired to observe the water vapor feature over the ocean at the leeward area that contains abundant water vapor. We developed the ship-borne analytic system for GNSS precipitable water vapor (PWV), which can estimate the PWV in real-time. Moreover, we investigated the impact of the oceanic water vapor for the forecast of the heavy precipitation event by the observing system simulation experiment. As a result, the accurate GNSS PWV was confirmed by the developed system; that accuracy was similar to the previous study. In the impact investigation, the forecast of heavy precipitation was corrected by the assimilation of oceanic water vapor, in particular, the data was necessary around the leeward area where the water vapor transport was significant.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2017/04 -2020/03 
    Author : Arimura Mikiharu
     
    Typhoon No. 10, which struck Tohoku/Hokkaido in 2016, caused flooding of bridges and large-scale landslides due to flooding of rivers in various places, causing catastrophic damage to the main trunk roads that support local communities. For such unusual weather, it is necessary to build a wide-area road network with a view to the future. Conventionally, river basin plans and ground maintenance plans and road maintenance plans have not been linked sufficiently from the viewpoint of disaster prevention and mitigation. In this study, we used traffic big data for large-scale meteorological disasters to grasp the impact of damage to a wide area road network over a long period of time. In addition, a road improvement planning method was developed to improve the resilience of the wide area road network in consideration of the potential road damage risk due to river and sediment disasters.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2016/04 -2020/03 
    Author : ISHIKAWA Tatsuya
     
    High-latitude zone like Hokkaido is an important region where it is expected to benefit and develop from global warming in future, while it is also expected that new types of geotechnical disasters, which never experienced before, will occur due to climate change. Therefore, in this study, we have constructed a theoretical system that reasonably explains the geotechnical disasters peculiar to snowy cold regions, which are different from the geotechnical disasters observed in warm regions, from the viewpoint of multiphysics (multiphase mechanics) and space-time multiscale by considering the interaction between thermal / hydraulic boundary condition changes and mechanical behavior in the normal to low temperature range. In addition, by using this theoretical system, we have proposed a hierarchical methodology that can evaluate the wide-area risk of geotechnical disasters in high-latitude cold regions occurred under near future weather conditions supposed by the climate change prediction.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2015/04 -2020/03 
    Author : Shimizu Yasuyuki
     
    This study systematizes a wide range of knowledge about the long-term dynamics of meandering, and builds the basic technology for realizing river development that makes full use of natural power and individuality. In particular, focusing on the meandering that determines the plane alignment of river topography, we deeply consider the fundamental mechanism of both short-term fluctuations due to sudden disasters and long-term topographical changes from past to future, and clarified the phenomena. In addition, we analyzed the various impacts on meandering, such as vegetation, presence of estuaries and river structures, diversity of meteorological and topographical geological conditions by theoretical analysis, field surveys, and simplified physical experiments. We also have constructed a computational model that can predict the meandering development transition considering various hydraulic conditions.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2015/04 -2019/03 
    Author : Yasunori Watanabe
     
    We found fundamental features of heat and gas transport in aerated ocean surface layers and modifications of surface drag in violent wave field through experimental parameterization of effects of sea sprays and bubbles entrained by wind wave breaking, computational identifications of heat and gas transfer owing to surface replacement under breaking waves, variable features of surface drag depending on transitions of three-dimensional vortex structures over ocean waves. As sea sprays dispersed in wind boundary layers disrupt the organization of the vortices formed over the breaking waves, causing transitions to fully developed turbulent boundary layer and modifications of surface drag. This process also changes the total momentum and heat fluxes between atmosphere and ocean.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2014/04 -2018/03 
    Author : Yamada Tadashi
     
    We suggested a way of mathematical scientific river planning excluding empirical factors. In conventional river planning, flood control standards such as design high water level are decided deterministically and single-valued, and the detail of river planning are based on these single-valued standards. However, there are uncertainties in hydrological quantities because of the differences in observation methods and their accuracy. In this research, we suggested a distribution of water level (uncertainty) obtained from extreme value statistical theory and runoff analysis method considering the uncertainty of hydrological quantities, and showed the distribution is extremely useful as a material to decide the timing of evacuation information. In addition, we method to introduce the effect of sediment and the resistance of the river channel shape as uncertainty into river channel design. This kind of mathematical scientific planning method is corresponding to new social awareness.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2015/04 -2017/03 
    Author : YAMADA Tomohito, Yadu Pokhrel
     
    Global hydrological cycle is affected by human activities such as irrigation, dam reservoir operation, groundwater pumping and domestic and industrial water consumptions. This study incorporated the land surface model including the dynamic human impact modules such into an Atmospheric General Circulation Model. Results showed that amount of irrigation water demand was approximately 3133 km3/yr which is comparable to observation and previous approaches based on land surface offline simulations and statistical models. The incorporation of the human impact modules into the AGCM showed reasonable sensitivity for surface air temperature against an original AGCM without those modules, and this is comparable to a previous study which adopts the impact of irrigation activity by surface water and heat fluxes as lower boundary conditions for AGCM.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2014/04 -2017/03 
    Author : YAMADA Yoshinori, HARA Tabito
     
    Studies based on observations and numerical models provided many findings on snow clouds producing heavy snowfalls and strong gust of wind. The analysis of Ku-band radar data revealed time changes in three-dimensional structures at convective scale of snow clouds at high spatial and temporal resolutions. Multi-Doppler radar analyses clarified characteristic airflow structures at meso β- and γ-scales in snow clouds producing heavy snowfalls, and wind recovery taking into account the surface vertical wind on complex orography suggested the importance of interaction between snow clouds and the orography for heavy snowfalls in Sapporo. A newly developed bulk microphysical model had better performance in reproducing snowfall patterns. Various processes important to the occurence and development of meso-α scale polar lows, sometimes accompanying heavy snowfalls and strong gust, were found by numerical experiments for winter seasons over past 30 years, using a regional model.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2015/03 
    Author : WATANABE Yasunori, YAMADA Tomohito, MORI Nobuhito, OTSUKA Junichi
     
    A novel numerical simulator to compute local behaviors of sea sprays and entrained bubbles produced by micro ocean wave-breaking processes, based on the stochastic turbulence model, was developed in this study. The model was confirmed to reasonably reproduce heat and gas transfer through advection and diffusions processes via gas-liquid mechanical interactions. Physical experiments for measuring the size distributions of sea-sprays and bubbles entrained into sea and the thermal radiation on the breaking-waves faces were performed in a wind wave flume. The momentum and heat transfer on the aerated ocean waves were found to be parametrized by the wind wave Reynolds number.The in-situ measurements for sea-sprays and air bubbles in ocean were also performed for characterizing mechanical contributions of the aerated ocean surface to the wave and current field.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2012/04 -2014/03 
    Author : YOKOKAWA Miwa, IZUMI Norihiro, HUGHES CLARKE John E., GREVE Ralf, YAMADA Tomohito, NAITO Kensuke, SUMIDA Takashi
     
    "Spiral troughs" (cyclic step topography) observed at the upper part of Mars' north polar ice cap is considered to be closely related to the formation history of the npc and thus the climate history of Mars. In order to explore the formation mechanism of this step topography, we operated analog experiments using ice. We also did the other experiment of cyclic steps by the gravity flows analogue to the sediment waves in the deep sea environments whose internal structures are resemble to those of spiral troughs on Mars. A theoretical model of interfacial wave formation between the fluid and ice is also created. In the analog experiments, we have succeeded in forming a interfacial waves that develop at the interface between the fluid and the ice by the flow in upper flow-regime. Behavior of these steps was consistent with that predicted by the theoretical model.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2010 -2012 
    Author : TANAKA Kenji, KANAE Shinjiro, HIGUCHI Atsushi, SHINODA Taro, YAMADA Tomohito, YOROZU Kazuaki, SOUMA Kazuyoshi
     
    The latest version of the coupled model CReSiBUC has been developed with the cloud resolving model CReSS version 3.4 and the land surface model SiBUC with new irrigation and snow processes. Based on the analysis of spatial pattern correlation of NDVI, two numerical experiments with different vegetation parameters for 2011 and 2010 were executed to investigate the relationship between the land surface vegetation status and Asian Monsoon variability which caused the 2011 Chao Phraya river massive flood.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2010 -2011 
    Author : YAMADA Tomohito
     
    This study suggested that realistic land surface initializations can contribute to sub-seasonal hydro-meteorological forecast skills in addition to other initial conditions in atmosphere ocean processes. Furthermore the sub-seasonal forecast skill for the1988US drought was improved by incorporating influences of human activities such as irrigation on the land surface initializations.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2009 -2010 
    Author : 山田 朋人
     
    本研究は土壌水分の初期情報を用いた水文水資源量の準季節予報スキルの評価を目的としたものである.申請者らのこれまで全球気候モデル(General Circulation Model ; GCM)を用いた研究成果において,土壌水分の湿潤状態は夏の降水量偏差に重要な影響を与える要因であることが明らかにされてきた.一方,地表面以深の土壌水分は初期値の影響(メモリ)が1～2か月間程度持続することが示唆されており,これは大気のメモリ(1～2週間)と比較して極めて時定数の長いものである.これらの研究成果を合わせると,土壌水分の初期情報は1～2か月(準季節)予報の精度向上をもたらす可能性を有するが,これまで科学的噂の範疇を出るものではなかった.本研究において,人工衛星や現地観測により得られたデータと陸面過程モデルを用いて計算される"準観測"土壌水分データを初期値としたGCMによる過去10年間の予報実験を行った結果,準季節スケールの降水量をはじめとする水文水資源量の予報精度がある程度改善されることが判明した.特に,1988年に北米を襲った大旱魃や同地域に大洪水をもたらした豪雨を2週間前以上前から予測するには,土壌水分の初期情報が必要不可欠であるという結果が得られた.

Educational Activities

Teaching Experience

  • Inter-Graduate School Classes(General Subject):Natural and Applied Sciences
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
  • Advanced Fluid Mechanics
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 工学院
  • Introductory Environmental Fluid Mechanics
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 工学院
  • Advanced Environmental Fluid Mechanics
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 工学院
  • Inter-Graduate School Classes(Educational Program):JICA Development Study Program
    開講年度 : 2021
    課程区分 : 修士課程
    開講学部 : 大学院共通科目
    キーワード : Disaster prevention; Natural disaster; Flood; Heavy rainfall; Tsunami; Liquefaction; Earthquake; Japan’s ODA
  • Advanced Fluid Mechanics
    開講年度 : 2021
    課程区分 : 博士後期課程
    開講学部 : 工学院
  • Introductory Environmental Fluid Mechanics
    開講年度 : 2021
    課程区分 : 博士後期課程
    開講学部 : 工学院
  • Advanced Environmental Fluid Mechanics
    開講年度 : 2021
    課程区分 : 博士後期課程
    開講学部 : 工学院
  • Hydrology, Water Resources and River Engineering
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 水循環，水文学，水資源工学，河川工学，水害，高水計画，洪水調節施設，流域土砂管理
  • International Project
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 国際プロジェクト，基準の国際標準化，教育研究の国際化，土木技術者の国際性
  • Hydraulics I
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 次元解析　相似則　静水圧　エネルギー保存則　運動量保存則 　摩擦損失　管路流
  • Exercise in Hydraulics Ⅰ
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 工学部
    キーワード : 次元解析 相似則 静水圧 エネルギー保存則 運動量保存則 摩擦損失 管路流
  • Freshman Seminar
    開講年度 : 2021
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 流れ，渦，波，自然災害，気候変動

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