[in Japanese]

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To use the Database for Policy Decision making for Future climate change (d4PDF) for the impact assessment of flood, it is important to develop a method to downscale and correct bias. This study proposes a method and validates the efficiency in the Omono and Hiji river basin. The results indicated that the dataset obtained by this study can reproduce historical extremes that was estimated using extreme value theory with small differences. From the results of the correction for future projections, the 1/100 year event will be happened in 1/50 year in both rivers. This dataset includes all AMeDAS stations excluding stations where available data is less than 20 years. The application of this dataset can contribute to reveal the future change of flood risk.

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A daily mean gridded temperature dataset of monsoon Asia (15S-55N, 60E-150E) for the period of 1961-2007 is created and open to public (Yasutomi et al., 2011) as a part of APHRODITE project(Yatagai et al., 2012). The number of stations used the interpolation analysis is up to 2 times the number of stations based on the Global Telecommunication System (GTS), which have been used to obtain other gridded temperature products. We obtained daily surface observation in collabollation with the local agency.
I introduce characteristics of its climatology and impact of increasing observations in Tibet and Himalaya region.

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[in Japanese]

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Multi-model ensemble regional climate scenarios with 1km horizontal grid-spacing over Japan are developed by using CMIP5 37 GCMs (RCP8.5) and a statistical downscaling (Bias Corrected Spatial Disaggregation (BCSD)) to investigate uncertainty of projected change associated with structural differences of the GCMs for the periods of historical climate (1950-2005) and near future climate (2026-2050). Each model projected different responses in near future climate because of structural differences. The most of CMIP5 37 models show qualitatively consistent increase of average and extreme temperature and precipitation. The developed ESD approach will be applied and extended to the CORDEX Asia region as a common benchmark for investigating uncertainty of regional climate scenarios and risk analyses. The added values of statistical/dynamical downscaling methods will be also investigated for locally forced nonlinear phenomena, extreme events.

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[in Japanese]

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[in Japanese]

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This study evaluates whether at identical levels of global warming, extreme precipitation and extreme discharge events are identical for transient and stabilized climates.
Using four Global Circulation Models and a global hydrological model (H08), four extreme-value series were computed on the 0.5 by 0.5 resolution grid, for all land surface. The series were then individually fitted to generalized extreme value (GEV) distributions using the L-moments method.
The statistical behaviors and the GEV distributions fitted to the extreme-value-series revealed that globally, all extreme indices presented large deviations. Differences in extreme indices between the transient and stabilized climates where small but significant while considering the influence of natural variability.
Since differences in extreme indices between the transient and stabilized climate are rather small and only affect a marginal portion of the land surface, relying on only the transient climate for assessing the impact of climate change on extreme events seams acceptable.

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Vegetation plays important roles in some hydrological processes, such as interception and ground water recharge. Therefore, vegetation change induced by climate change may have negative impact on water cycle. Many researchers have analyzed climate change impacts on water cycle in recent years. However, few of them take into account the impacts of vegetation change. This study performed an analysis of climate change impacts using meteorological, dynamic vegetation and hydrological models. We compared the results with those obtained by a conventional method using only meteorological and hydrological models in order to assess the effect of the vegetation model.

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This study evaluated the changes in river discharge due to climate change using an integrated water resource model. This model, a combination of Simple Biosphere Model(SiBUC), Rainfall-Runoff-Inundation Model (RRI) and Reservoir Operation Model (ROM), considers the impact of reservoirs on the hydrological cycle and allows description of water and energy at the basin scale. The results annual River discharge trends to decrease. But there are no obvious changes in winter though precipitation trends to decrease. The probable reason is an increase of snow melting. In the heavy rainfall season from June to September, the average monthly discharge will decrease from present to future excluding July. There is an obvious decrease in August from present to future. Peak flow in September seems to move forward from late of the month to early of the month. Extreme flow (daily maximum) tends to increase during the projected period. Generally, the decrease in total discharge and increase in extreme discharge will bring large challenges to future water resource management.

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In recent years, flood damage caused by heavy rain that exceeds the plan scale is frequent. Recently, high

importance of excess flood measures is recognized with uncertainty of external force. External force scale and uncertainty are assumed to be increased by climate change. For this reason, it is highly necessary for a new flood planning theory by considering uncertainties by rational methods. In this paper,we suggested excess flood measures by d4PDF precipitation data. (1)Evaluation of uncertainty due to the difference in the probability distribution : GEV distribution is higher goodness of fit than Gumbel in the climate change condition because extreme events are remarkable. (2) Evaluation of uncertainty as excess flood measures: GEV distribution has larger uncertainty than Gumbel, it exceeds probable maximum precipitation in climate change condition.

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Afforestation is expected to be an adaptation measures for reducing flood in Chao the Chao Phraya River Basin since both of the global warming and deforestation are worried to increase floods. In this study, changes in runoff cuased by the warmed climate and afforestation are examined by conducting numerical experiments using a land-surface model, where effects of vegetation canopy are explicitely considered. The present and warmed climate conditions are specified, and 20% of cropland are changed into natural vegetation to mimic afforestation. Under the most-warmed climate senario, precipitation is increased by 350-430 mm/yr at the end of 21C, and runoff is increased by 200-280 mm/yr. The runoff increase is reduced by 1.8-5.5 mm/yr by a mimic afforestation. That corresponds to 0.4-1.2% of the volume of the two major dams in the basin. The reduction of annual runoff at a unit area of afforestation is 65-75 KCM.

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[in Japanese]

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The Guerilla-heavy rainfall (GHR) occurrence has increased in numbers. In 2008, five people died due to the occurrence of GHR in Toga River, Japan. It is very important to GHR and predict the occurrence of The rapid scan observation (RSO) of Himawari-8 is very useful to investigate the cloud development process because of its fine temporal and spatial resolution (0.5 - 2 km, 2.5 minutes). To maximize the utilization of RSO of Himawari - 8 data, in this study we utilize some of the parameters to investigate the relationship between cloud top condition and hydrometeor type aloft. The preliminary investigation shows a potential correlation between hydrometeor types aloft and cloud top conditions.

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Water scarcity is a global concern that necessitates a global perspective, but it is also the product of multiple regional issues that require regional solutions. Water markets constitute a regionally applicable non-structural measure to counter water scarcity that has received the attention of academics and policy-makers, but there is no global view on their applicability. We present the global distribution of potential nations and states where water markets could be instituted in a legal sense, by investigating 296 water laws internationally, with special reference to a minimum set of key rules: legalization of water reallocation, the separation of water rights and landownership, and the modification of the cancellation rule for non-use. We also suggest two additional globally distributed prerequisites and policy implications: the predictability of the available water before irrigation periods and public control of groundwater pumping throughout its jurisdiction.

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In this study, we verified using WRF and RRI model for the purpose of clarifying whether the possibility of flooding could be detected several days ago. The predicted rainfall is calculated using WRF-LETKF by 33 ensemble members for the next 72 hours every 6 hours. The hydrological model used the RRI model, which has a spatial resolution of 2 seconds (50 meters) mesh.
At 9 o'clock on 4 July, 4 members predicted exceeding Evacuation W.L. of all 33 members, of which 2 members can predict Danger W.L.. At 115 o'clock on 4 July, 2 members predicted exceeding Evacuation W.L. of all 33 members, of which 1 members can predict Danger W.L..
Therefore, in this study, we found that it is possible to detect the possibility of flooding 21 hours ago by ensemble prediction.

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Flood prediction is one of the basic soft countermeasures for safe evacuation and disaster risk reduction of water-related disasters. The current flood forecast predicts how river water levels will change in the next few hours at river sections where water levels are observed. In recent years, flood predictions with a distributed model have been also practically applied due to detailed topographical data and quantitative radar rainfall information. However, the following two problems still remain in the current flood forecasting. One is that river sections other than observation points are out of prediction target, and the other problem is that the situation of flood inundation caused by overtopping or torrential rain is out of the scope of real-time flood predictions. In this study, we report on the recent development of flood predictions including river flow discharge, water level and flood inundation even along small rivers in river basins. Specifically, we will report the results carried out for the Chikusa River basin (covered area 777.6 km²) of Hyogo prefecture and describe the future prospects including the application of the model at the national level.

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Topographical characteristic, meteorological characteristics, and artificial characteristics (human activities) cause flooding in urban areas. Jakarta rapid development gives an urbanization impact to its suburbs. Accordingly, Tangerang city, as a suburban area of Jakarta, facing that effect. The proposed methodology in this research is based on GIS computation of the frequent inundation areas in Tangerang between 2008 and 2015. We extracted its topographical characteristics and analyzed it to find a correlation between topographical elements and frequent inundation areas. Thus, we applied its topographical element score for all mesh across the city. As a result 78. % of Tangerang city area is classified as high-risk topographical inundation, then only 54. % of the frequently inundated areas and 85. % of ordinary inundated areas are considered to be in high-risk zone. The result indicates that topographical characteristic alone is not sufficient to explain the emerging of an inundation area.

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Woody debris (WD) in rivers are mainly caused by a combination of biological, physical and artificial factors. Furthermore, by the frequency of strong torrential rains due to the global warming, large scale disasters due to WD have become more frequent in recent years in Japan. For the effective countermeasure against these disasters, it is important to deepen the understanding a series of WD transport process, which are generation, sedimentation/transportation, and discharge. In this research, we developed a prototype of the world’s first physical model based on a series of WD transport process and estimate WD sedimentation in 5 dam reservoirs in Kitakami River.

The Nash-Sutcliffe values were 0.7 or more for WD transport calculated using this model except the Shijusida dam reservoir. From the comparison of storage parameters in this model, the Yuda and Gosho dams have relatively much WD sedimentation in the watershed than the Tase and Ishibuchi dams.

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Recently, a few studies have proposed to utilize deep learning algorithm for flood forecast. This study utilizes Recurrent Neural Network with Long-Short Term Memory as the basic structure. Additionally, to extend lead time retaining the prediction skill, this study adopts a hydrology-inspired preprocess method and an adaptive sequential structure. Exponential Filtering translates rainfall to have proper delay in accord with the variability of basin water storage based on water budget equation. The adaptive structure attaches predicted water level as additional input node of the neural network at a subsequent prediction . In the case study in Kinu river basin during the Kanto-Tohoku heavy rainfall in September 2015, the application of the extended algorithm with two additional treatments efficiently reduces error in expanding lead time.

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We investigated about fat-tail distribution, namely Levy distribution, GEV and Gumbel distribution for extreme precipitation time series data. As a result, we found that tail of Levy distribution is too fat and GEV or Gumbel distribution is more appropriate. Moreover, we investigated mono-fractal model for describing time series of hydrological (quality) data. fBm and fLm are often used but we found that fBm-like model with GEV of Gumbel distribution are potintial candidates for describing the time series.

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[in Japanese]

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Young Researchers Association of Japan Society of Hydrology and Water Resources (JSHWR) (hereinafter, YRA) is a research group composed of young researchers in their twenties to thirties. YRA has continued interdisciplinary discussions among several research fields and exchanged opinions on interdisciplinary research collaboration since 2009. As we found these activities are helpful for gaining new perspectives and for making progress in our own research, it is essential to expand interdisciplinary discussions with more new members. On these backgrounds, YRA 2017-2018 conducted 1) an interdisciplinary seminar among young researchers, 2) a research presentation workshop and 3) writing review paper in JSHWR by YRA members.

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In River Basin, ecosystem and water environment are affected by natural disaster such as flood, sediment disaster and snow disaster. To resolve the problem by revealing the phenomenon in river basin, transdisciplinary research that is integrated various disciplines such as hydrology, agriculture, meteorology, ecology and sociology should be pursued.Therefore, this research group conducted 1) research seminar of river basin study and 2) excursion and workshop of river basin study in this year. We are going to report these activity in the conference.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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Snowmelt and meteorological observation was conducted at three Japanese cedar stands and an opening. The stand densities of the three were sparse (the cedar stand A), moderate (B) and dense (C). From 1st April to the date of snow disappearance net radiation accounted for 88.4%, 43.0%, 32.7% and 34.2% of total snowmelt energy at the open site, the cedar stand A, B and C, respectively. The ratio of sensible and latent heat to total snowmelt was 33.1 % to 37.9 % and 25.9 % to 29.4 %, respectively, at three cedar stands. The ratios of sensible and latent heat increased over time in accordance with the rise in temperature at all cedar sites. They became large on a daily basis when air temperature and/or wind speed were high.

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As the water crisis is becoming more serious year by year, it goes without saying that there has been an urgent need for a water and heat supply analysis model with higher accuracy. In previous research, it has been shown that Land Surface Process Model SiBUC is likely to overestimate the heat supply at a high altitude of a glacier. In this research, several analyses are done on the hypothesis that temperature overestimation at a glacier is caused due to the temperature interpolation that follows dependency on elevation, that is, the discrepancy occurs because the temperature at a highly located area is calculated by using the temperature at a low area with no snow simply depending on elevation. As a result, it turned out that the overestimation is likely to occur in daytime.

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High-frequency monitoring of streamwater nitrate concentration was conducted in a forest catchment using an optical sensor. This is the first attempt in Japan. It was revealed that not only the actual export of streamwater nitrate but short-term hydro-biogeochemical dynamics during storms within the catchment.

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The characteristics of radioactive cesium runoff was examined at a small forest catchment in the Abukuma mountains. As a result, it was about 0.03-0.10% in the runoff ratio of Cs-137 to a total deposition amount in three years of 2014 - fiscal year 2016. It has been understood that a big flood event strongly influences the outflow of Cs-137.

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We investigated water quality of deep artesian wells in Yokkaichi city. 70% of source of drinking water in Yokkaichi city is ground water, then investigating quality of ground water as well as quantity of that is quite important. This is our motivation of the research. As a result, we found that deepness of well strongly affects to quality of water in wells; namely, for example, the more the deepness of wells is, the more concentration of Na+ is and the less concentration of Ca+ is.

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Since the latter half of the 1990s, reducing nutrient salt has become serious in Harima Nada, in order to solve the problem it is urgent to implement proper nutrient salt management. In this study, as a basic research of long term nutrient salt analysis, we constructed hydrological and water quality models and analyzed total nitrogen dynamics in the Kako River, which has the largest catchment area among the inflowing rivers that supply nutrient salt to Harima Nada. Total nitrogen sourcesincluded point sources and rainfall-runoff driven area sources. [s1] The models well reproduced river flow rate, but overestimated total nitrogen concentration after rainfall. This suggests that an improvement in area sources is required to better simulate nitrogen behavior in the basin.

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The Long- and Short-Term Runoff Model combined with LQ equations of power type was developed as a solute load estimation model and it was applied to a small forested experimental catchment in Nara Prefecture which sodium concentration data were observed with high frequency. The model parameters were identified by using solute load observed with equal intervals of 10 minutes, 1-day, 4-day, 7-day and 14-day and estimation errors of solute load obtained by optimized model were examined. The results show that estimation error become large when the data with observation intervals larger than 4-day are used for parameter identification. The model parameters were also identified by using solute load with sampling intervals based on equal cumulative runoff and the model performance were very good even if the number of observed data is small.

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It is aimed to analyze under what conditions the thermals generated by the heat and shape effect of the city breaks through the atmospheric boundary layer to generate cumulus clouds. Using the urban meteorological Large Eddy Simulation model, the thermals over Kobe City were targeted. As a result, the validity of the model was also assessed using the boundary layer radar. Two factors were confirmed on the thermals which break through the atmosphere boundary layer. One is strong thermal buoyancy, and the other is elimination of the stabilizing layer by another thermal. In addition, the relationship between the thermal and the vortex tube is also suggested, and further analysis will be carried out in the future.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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Studies on hilsllope hydrology have found the diversity of stormflow pathways and the flow interactions in them. As far as the total amount of stormflow is neary equal to that of rainfall during a large magnitude storm event, however, the stormflow response can be comparatively easily analyzed using the therory of soil physics as a waveform conversion from the hyetograph to the hydrograph because all the pathways including the soil matrix and preferential pathways in a hillslope soil layer have to be activated for contributing to the stormflow response. This presentaion aims at detecting a generality from diverse stormflow mechansims needed for a possible development of physically-based runoff models.

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A high-resolution hydrography data is an important baseline data for remote sensing and modelling of river hydrodynamics, given the spatial scale of river network is much smaller than that of land hydrology or atmosphere/ocean circulations. For about 10 years, HydroSHEDS, developed based on the SRTM3 DEM, has been the only available global-scale hydrography data. However, the data availability at the time of HydroSHEDS development limited the quality of the represented river networks. Here, we developed a new global hydrography data using latest geodata such as the multi-error-removed elevation data (MERIT DEM), Landsat-based global water body data (GSWO & G3WBM), cloud-sourced open geography database (OpenStreetMap). The new hydrography data covers the entire globe (including boreal regions above 60N), and it represents more detailed structure of the world river network and contains consistent supplementary data layers such as hydrologically adjusted elevations and river channel width.

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To better assess hillslope stability for a correct landslide prediction, one requires a precise model for simulating three-dimensional groundwater table within a hillslope. This study presents our recent development of a depth-integrated model for shallow subsurface flow in unconfined hillslope aquifers. With the depth-averaging method, we have derived a perturbation solution of Boussinesq-type groundwater table equation. The leading-order evolution equation having strong advection, nonlinear diffusion and source terms is used for numerical solution. To efficient and accurate numerical calculation, we utilized a new relaxation scheme of high-resolution Godunov-type finite volume method. A special numerical treatment to the nonlinear diffusion term is adopted for assuring the property of numerically well-balancing. To better model real subsurface flow, a theory for unsaturated zone is also involved as a correction in our model. Some cases are conducted for verifying our new model. This work is supposed to provide a new model for efficiently simulating the three-dimensional subsurface flow in unconfined hillslope aquifers.

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[in Japanese]

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Central Asia has been seriously impacted over the water resources availability. One of the important issue in the region is increased salinization of the soils and the water mineralization moving to the downstream of the river flow of all major rivers in the region. Arid climate implies increased evapotranspiration rate that consequentially increases sedimentation of the water containing salts after drainage waters are flown back to the river streams. Furrow irrigation that is common here, floods fields with great amount of water that serves two purpose, first it increases soil water saturation and second removes salts from the soils. However, this cost in decreasing water quality all the way to the downstream of the river flow. Here we investigate impact of the salinity impact to the crop water demand and water quality following river flow. In this research we investigate these issues on the case study of Zeravshan river basin.

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An integrated flood risk management (FRM) plan was established in the Philippines for the first time in 2012 after the disastrous flooding brought by Typhoon Ondoy in 2009. It is a crucial task to identify and analyze the barriers that may hamper the effective implementation of the FRM plan. In this study, barriers to FRM were identified from a collection of literature related to flooding then interrelationships among barriers were analyzed by conducting a pairwise assessment by experts. Barriers to FRM in Metro Manila are found to be related to three aspects. There are 4, 3 and 5 barriers identified in the governance, social and scientific resources aspect, respectively. The barrier interrelationships was elicited by 5 carefully selected local experts and practitioners in the Philippines.This study was that barriers in the social aspect of the barriers while the barriers on the social aspect of the barriers while the social aspect the most influence but strongly depends on the other aspects. This study was able to identify and analyze the interrelationship of each FRM barriers which can provide insights to decision makers on how to overcome them.

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In this study, we aimed to grasp the seasonal variation of the water quality in Mak Hiao River which runs in and receives waste water from Vientiane, Lao PDR. The field survey was conducted twice in the rainy and dry season. As a result, total nitrogen, total phosphorus, phosphate phosphorus and toral organic carbon gradually increased flowing downstream in the rainy season and decreased as flow through the suburban area in the dry season.

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In this research, a first trial of NHRCM 5km simulation result in Thailand provided by Japan Meteorological Agency Meteorological Research Institute (JMA/MRI)is evaluated from river discharge view point. First, the accuracy of NHRCM 5km rainfall data is evaluated by comparing with APHRODITE observation data. The result shows underestimated value in the most of region in Thailand, except in the northern region which almost corresponds to Bhumibol dam catchment. The river discharge simulation is perfomed in the upper catchment of Bhumibol dam (area: 26,000 km2) using a coupled of SiBUC and 1K-FRM model. Overall, the river discharge simulation shows consistency result with rainfall analysis.

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[in Japanese]

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This report overviews research activiteis of Theme C: Integrated Climate Change Projection in Integrated Research Program for Advancing Climate Models. There are three components in Theme C: (i) integrated climate model, (ii) versatile climate scenarion developments and mechanisims in future climate changes, (iii) international cooperations. We develop future climate scenarions using the global and regional climate models' system for dynamical downscaling of future climates in MRI, featuring the global dynamical downscaling instead of CMIP5 atmosphere-ocean couple models. We presents two research outcomes: future changes in 1-hr heavy rainfall with MRI-NHRCM with 2 km grid spacing and future changes in typhoons with a large ensemble of atmospericl MRI-AGCM3.2 with 60 km grid spacing.

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Downscaled six GCM outputs with three RCP scenarios in the CMIP5 around the Tatsunokuchi-yama Experimental Watershed (34° 42′N, 133° 58′E), where drought risk is relatively high even in the present climate, have less annual precipitation in both amount and frequency; in particular, frequencies of daily precipitation no greater than 20 mm were clearly few. These biases were diminished by our contrived simple correction method using monthly mean values of relative humidity and solar radiation in actual rainy days. According to simulation results in 2015-2100 by seven runoff models tuned for different subsurface geology, the precipitation corrected data caused increase of ensemble minimum values among the GCMs in each scenario. Although our precipitation correction method changes only slight amount, it is concluded that our method can mitigate overestimation of drought risk derived from shortage of precipitation in both amount and frequency of original climate scenario data, without change the trend of GCM output.

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