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.

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Some rain-gauges produce a disturbance of the air currents which is called "Jevons effect", thereby a disturbance in the distribution of precipitation of such a kind that a part of the rain is carried past the rain-gauge, and the amount of variation from the true rainfall increases with increasing wind velocity. To evaluate the capture ratio when a strong wind occurs, the 9 m2 huge rain-gauge was invented that could reduce and neglect the Jevons effect. The total amount of rainfall for three months observed from the huge rain-gauge is about 5 % greater than that observed from the standard rain-gauge. 2-dimensional video disdrometer analysis showed that the capture ratio was low during the rainfall which had the small median diameter of the raindrop size distribution.

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Cloud Microphysics Data Assimilation System (CMDAS) was developed to improve water vapor and cloud liquid water content in numerical weather prediction model by assimilating brightness temperature data observed by satellite-mounted microwave radiometer. In the optimization scheme in CMDAS, cloud bottom height (CBH) information is used to define vertical profiles of water vapor and cloud liquid water content which are necessary in a microphysics parameterization scheme. Cloud bottom height varies with atmospheric conditions, however, a constant value is used in CMDAS. In this study, effects of different CBHs on assimilation and numerical weather prediction with assimilated initial conditions are examined.

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Recent development of X-Band Radar system in Japan is expected to provide more accurate and higher resolution rainfall estimates, which may lead to improve flood forecasting through rainfall-runoff predictions. However, the effect of enhancement of rainfall observation has not been well investigated quantitatively, mainly due to the luck of systematic evaluation methods. This paper presents a statistical model to analyze uncertainty structures in radar rainfall estimates and stochastic rainfall generator to represent the uncertainty structures including variance and spatial correlation. The proposed method is applied to C-band and X-band radar data in Kinki region, followed by runoff analysis in Hiyoshi dam reservoir catchment. Based on the simulation results, the uncertainty propagation characteristics are described in radar rainfall fields to runoff.

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Localized torrential rainfall caused heavy rainfall disasters in Summer and Baiu season of Japan called as "Guerrilla-heavy-rainfall" in Japanese media.The rainfall was produced by an isolated cumulonimbus that grew rapidly.To prevent these disasters, Japanese government recently installed networks of X-band polarimeric Doppler radars over major urban areas in Japan.X-band radar is suitable to realize earlier and more detailed detection of the baby cell, because X-band radar has higher sensitivity and spatial resolution.This research investigates the growth of the baby rain cell to become large cumulative clouds by focusing on its vorticity using Doppler velocity.In this research, we define two vortexes with different size, and evaluate a relationship qualitatively between rainfall and the existence of vortex.

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We focus on the Probable Maximum Precipitation (PMP) over the Upper Tone River basin, through maximization of weather conditions. In order to evaluate vertical and horizontal distributions of weather conditions during heavy precipitations, Grid point value (GPV) data from meso-scale objective analysis is used. The results are summarized as follows: (1) Moisture fluxes have higher correlation with typhoon rainfalls than precipitable waters which are the basic index to maximize precipitation under the WMO method. (2) Moisture fluxes between 850 and 800 hPa have high correlation with the data observed at the surface. Converted past heavy surface moisture fluxes into moisture fluxes between 850 and 800 hPa showed high correlation coefficient of more than 0.8 with rainfall by major typhoons. (3) PMP was calculated from the past maximized moisture flux ratio for major typhoon rainfalls, and it exceeds the maximum observed rainfall in the area.

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In 2010, severe floods in Pakistan brought many casualties and economic losses. The heavy rainfall in this year was the greatest since 1994. This study presents a challenge to attribute the 2010 Pakistan heavy rainfall to global warming. We analyzed large ensemble simulations of a general circulation model (GCM) both under realistic climatic conditions and under ideal climatic conditions assuming global warming is not occurring. Due to inherent model biases in rainfall representation in the GCM, we defined a proxy indicator which could illustrate the specific atmospheric pressure pattern causing heavy rainfall in Pakistan. The probability density function (PDF) of the indicator showed that the pressure pattern associated with the heavy rainfall seems to be slightly reduced on average due to anthropogenic climate change, but there was minimal change for the extreme cases.

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Recently, localized heavy rainfalls over heavily urbanized areas have caused severe damage in Japan. On 5 August 2008, a localized heavy rainfall caused a rapid increase in drainpipe discharge, which killed five people working in a drainpipe near Zoshigaya, Tokyo. This study investigated the effect of actual land surface initial state on this localized heavy rainfall by two ensemble experiments using a cloud-resolving model that included precise urban features. The first experiment (ACTD) considered realistic initial land surface state derived from off-line land surface model calculation using meteorological observation provided by Japan Meteorological Agency. In the second experiment (CTRL), the initial soil moisture was set to homogeneously wet condition, and the initial land surface temperature was set to the same value as near surface air temperature. The amount of rainfall was significantly increased and close in the observed value over Tokyo at the beginning of rainfall in the ACTD experiment. The larger land surface temperature over urban area and larger soil moisture over surrounding area caused stronger contrast of surface heating in ACTD experiment. The contrast of surface heating caused the contrast of near-surface air temperature and intensified the convergence of horizontal wind and updraft over the urban area, and resulted in the larger amount of rainfall at the beginning of rainfall.

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X-band polarimetric radars (X-band radars) have an advantage in observational resolution temporally and spatially over conventional C-band radars. We developed the new nowcasting method utilizing observation of X-band radars for the improvement of localized heavy rain predictability. First, precipitation distribution is separated into small- and large-scale components, corresponding to convective and stratiform precipitation, through wavelet transformation. Prediction is improved by compositing the extrapolated distribution for each scale. Predictability is further improved by including the time development of small-scale component based on the analysis of precipitation characteristics.

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Urban localized heavy rainfall has become a serious issue especially during summer in the Tokyo metropolitan area. In order to analyze its relationship with urbanization, improved urban parameters were implemented into WRF together with high spatial resolution sea surface temperature (SST). For the simulation, the aerodynamic parameters such as roughness length and displacement height were prepared using a new feedback parameterization derived from large eddy simulations of real urban morphology. Applying the new urban parameterization realized a more accurate simulation of localized heavy rainfall. The stagnation of heat and water vapor around city, and also the delay of sea breeze caused by the drag of urban geometry, increased heavy rain in Tokyo.

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Characteristics of localized heavy rainfall in the Fukuoka metropolitan area are investigated on the basis of field observation data taken with 14 rain gauges and 76 thermometers. The surface temperature in the case of localized rainfall shows an increase of about 2°C compared to that in the absence of rainfall. The vertical distributions of the humidity in localized rainfall and no rainfall cases differ obviously at elevations higher than 900hPa, whereas there is no difference between both near the ground. The present study shows that the indexes of the air stability, i.e., SSI, LI, KI and CAPE may be useful for detecting the occurrence of localized raifall in this urban area.

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In recent years, rainfall forecasting technologies have been advanced remarkably and some forecasts with high accuracy have been applied to dam operations practically.In this study, the accuracy of Japan Meteorological Agency' s Global Spectral Model Grid Point Value (GSM-GPV) of leading time of 192 hours at Kumano river basin and the accuracy of the efficient formulation of GSM-GPV for use of dam operations have been examined. Further, a new weather forecasting method, which combines the efficient formulation of GSM-GPV and the information about typhoons, has been proposed and tested. The results showed that the new method had the applicability to dam operations in terms of the reductions of dam flood discharge.

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There is growing concern on a global scale about the significant increase of extreme meteorological events in recent years, e.g., torrential rains, heavy snows, and severe hurricanes. The current study conducted frequency and scale analysis of torrential rains to examine future variations of rainfall events due to global warming, based on GCM (Global Climate Model) outputs calculated under the present condition (1979-2008), near-future condition (2015-2044), and future condition (2075-2104) by the KAKUSHIN Program of the Ministry of Education, Culture, Sports, Science, and Technology (MEXT). DAD analysis was also attempted to clarify whether and how the statistical relationship will change in the future with global warming between maximum areal rainfall and the area and duration of each rainfall event. Results show that the occurrence frequency of torrential rains could markedly increase in some regions of Japan, and that DAD relationship could significantly change in the future, and there could be a numerical increase in rainfall events which depart from the regression curve of DAD relationship due to a greater rainfall intensity or larger area of rainfall than most other events. Visual inspections of each event suggest that such extreme events could be attributed to Baiu front activated by the sufficient amount of water vapor and typhoons strengthened by the higher sea surface temperature due to global warming in the future.

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Heavy precipitation induced by a typhoon often causes a severe disaster. In this study, we aim to propose a statistical method to project extreme precipitation caused by typhoons in the future. Our method is a combination of a stochastic typhoon model, statistical precipitation analysis, climate model outputs, and a physical basis for changes in precipitation. Our method was applied to the Kagami river basin of Kochi. While the number of typhoon approaching Kochi is projected to slightly decrease or unchanged, 2-day extreme precipitation induced by typhoon is projected to increase in the last twenty first century (2081-2100). The projected values are widely different according to a method to estimate changes in precipitation. We also estimated the future return period of heavy rainfall causing the largest recorded flood of the Kagami River.

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The difference of bias-corrected daily extreme precipitation in 21st century simulations among GCMs, RCP scenarios, ensemble runs or bias-correction methods are focused in this study. We use 8 GCMs, 2 RCP scenarios and 3 bias-correction methods to estimate the future precipitation. The estimates obtained are compared each other and the degree of the difference caused by the selection of each component to estimate are evaluated. In addition to these three components, the difference of three ensemble runs from only MIROC5 is used to evaluate. The evaluation is conducted in the historical as well as future simulations. The results indicate that the difference is not significant in the historical, but it is significant in the future. We applied a clustering method to estimates in the future. The clustering obtained indicates that the difference caused by the difference of bias-correction methods is comparable to that caused by GCM, RCP or ensemble runs.

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This study investigates the predictability of Thailand more-than-normal rainfall in 2011 from pre-monsoon to rainy season, which induced severe floods and immense damages, by incorporating seasonal prediction conducted by a general circulation model (GCM) and downscaling based on Singular Vector Decomposition (SVD) analysis. Our coupled atmosphere and ocean GCM has ability to predict tropical sea surface temperature (SST) in seasonal timescale. Taking this advantage, we derived statistical relationship between a large-scale tropical SST field and regional rainfall over the Indochina Peninsula using SVD analysis. Based on this transform function, SSTs predicted by the GCM were translated into the predictand of regional rainfall. Our final prediction products well captured the more-than-normal rainfall during the pre-monsoon and the late-monsoon seasons in Thailand 2011, while the rainfall in the early-monsoon season was underestimated due to less seasonal predictability of SST in the Indian Ocean.

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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.

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Due to rainfall during the snowmelt season in May 2012, landslides occurred at Nakayama Pass, which is on the main route between Sapporo and Southern Hokkaido, and all lanes there were temporarily closed for the first time since the route opened in 1969. Quantitative evaluation for the risk of landslide such as that at Nakayama Pass during the snowmelt season has remained an issue. In this study, we proposed a method for quantifying the soil moisture of potential landslide sites by comprehensively estimating the long-term water cycle of the watershed. As the result of applying the proposed method to the Nakayama Pass landslide site, it was clarified that the soil moisture of the landslide site at the time of the May 2012 disaster was the highest in the previous 33 years. This proposal was considered effective for quantitative evaluation of the soil moisture associated with landslide during the snowmelt season.

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For better estimation of snow water equivalents for a dam basin in cold snowy regions, the relationship between snow depth distribution outside forests and topography was investigated using high-resolution digital elevation model (DEM) created from airborne laser scanning. A linear relationship between snow depth outside forests and overground-openness was clarified. A method to estimate snow depths and snow water equivalents outside forests was developed using this linear relationship. Using the method, snow water equivalents in the Chubetsu Dam basin were estimated and resulted in estimates with a higher level of accuracy than those based on existing methods.

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We predicted the hydrological impact of glacier retreat in the glacierized catchment located in Bolivian Andes by applying a grid-based physically distributed runoff model. The capability of the model was improved by including snow and ice melt processes, in which temperature, solar radiation and humidity were taken into accounts based on our field observation. Runoff retarding by the freezing soil was also considered. Given hourly meteorological conditions and spatial distributions of land cover, precipitation and air temperature, the model result agreed well with observed flow rates. After the full glacier retreat, the flow rate is estimated to be significantly reduced in the dry season while the impact is less in the wet season. We found that glacier melts mostly occurred in the early stage of the wet season. In addition to glacier disappearance, the rise in air temperature increased the discharge during major precipitation events but reduced the amount of snow accumulated over the catchment.

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A simple method that estimates spatial albedo distribution on glacier using satellite images was developed. Glacier for this study is Condoriri glacier in Bolivia. An albedo- radiance relation is derived from a power function. Both observed albedo 0.08 on end moraine and maximum albedo on fresh glacier were used to decide constant numbers for all images on the assumption that they do not vary with time. As a result, 0.65 was decided as maximum albedo after optimization for a correction function of albedo. We evaluated the accuracy of calculated albedo using albedos 0.18 on bare ground. RMSE (Root Mean Square Error) indicates 0.091 on bare ground. Calculated albedos on all ground coverage by this computation method were in agreement with data from other estimation.

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The tropical glacier in Andes Mountain has summer precipitation seasonality. A multi-layer snow model was applied to Zongo glacier, Bolivia to evaluate the heat balance on the glacier and the effect of snow on glacier melt. Model simulation at observation point successfully accounted for variations in surface temperature on the glacier in both dry and wet season. Main components of melt heat were shortwave radiation in the dry season and long wave radiation in wet season. Melt flux in mid-wet season was lower than in early-wet season due to continuous snow cover and its high albedo. Moreover, simulation results showed that snow cover on the glacier decline the melt rate in the wet season. This result suggests that mass balance is affected by summer precipitation seasonality and vulnerable to temperature rise.

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Seasonal frozen ground area on the Tibetan plateau has particular land surface condition with frozen ground and patchy snow distribution. The existing satellite microwave remote sensing was therefore unable to estimate the snow quantity exactly. An evaluation method of snow area proportion based on AVNIR-2 and MODIS over the seasonal frozen ground area on the Tibetan plateau was therefore devised in this study, and it was introduced to estimated snow depth based on Tsutsui and Koike (2012) 's snow estimation method. In the result, we were able to compare the estimated snow depth with the in situ snow depth data, and the relatively good agreement was recognized. Simultaneously the availability of the Tsutsui and Koike (2012)'s snow estimation method and the evaluation method of snow area proportion based on AVNIR-2 and MODIS was recognized.

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Global- and continental-scale snow simulation has been used to produce snow estimates and attribute the change of snow into hydrological variables. However, uncertainties in global- and continental-scale snow simulation due to model structure, model parameters, and meteorological forcing has not been well documented. In the present study, we used MATSIRO land surface model and conducted ensemble simulations for snow, i.e., perturbed parameter ensemble simulation and multi precipitation ensemble simulation. The results show that uncertainties in parameters are larger in the melting season than accumulation season and uncertainties in precipitation are large in accumulation seasons. The uncertainties of parameters in melting season are comparable to that of precipitation.

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A change of water resources in the late 21st century at the Pasak River basin in Thailand is analyzed using a distributed rainfall-runoff model and a rainfall and evapotranspiration output projected by MRI-GCM3.1S. The main findings are as follows: a projected mean annual inflow to the Pasak Dam reservoir for the near future and the late 21st century experiments decrease by 3.8% and 3.5% compared with the present climate experiment; a projected mean monthly inflow using the output of the late 21st century experiment decreases except from July to September; and to maintain a present dam outflow is difficult in the future under a scenario of the same water demand.

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Super high-resolution AGCM precipitation outputs of Meteorological Research Institute, Japan Meteorological Agency (MRI-AGCM 3.1S and 3.2S) for emission scenario A1B were utilized with their bias correction so as to obtain the precipitation patterns over West Rapti River basin for present and future periods. A hydrologic model, PDHM Ver.2 was employed to obtain the time series of daily river discharges for the above mentioned time durations followed by frequency analyses for probable flood discharges of 25- and 50-year return periods. Flood inundation simulations of 50-year return period events for Present and Future were carried out with the Rainfall-Runoff-Inundation model followed by a flood risk assessment based on the simulated flooding depths and durations for household and agriculture over the target area. Future flooding depths in the area show a significant increment compared to the Present situation despite of their relatively big uncertainties. These variations in Future climate will cause complex implications on the adaptation strategy.

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Recent development of a rainfall-runoff-inundation (RRI) model allows simultaneous simulation of river discharges and flood inundations in large river basins. Because of the structural simplicity with fast computation, the model is suitable for flood risk mapping with climate change projections. To meet the objective, however, it is necessary to test the model ability for long term simulations. This study employs land surface model (LSM) output of actual evapotranspiration for forcing the RRI model over the period of 1980-2004 in the Chao Phraya River basin. The first simulation result with parameters calibrated for 2011 floods was not satisfactory. The RRI model could not hold sufficient soil water in dry seasons to meet the evapotranspiration demand by the LSM. As a result, the model overestimated the annual runoff. To solve the issue, the subsurface model in mountainous area was updated to incorporate unsaturated zone with thicker soil layer, which improved significantly the simulation results of monthly runoff at various locations.

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Spatio-temporal information on the sources of flooding is essential for effective flood control and for a holistic understanding of water quality dynamics. Nevertheless, monitoring such information has been extremely challenging, particularly in the case of large-scale flooding. This paper proposes to estimate the information of flood sources by using a rainfall-runoff-inundation (RRI) model and time-space accounting scheme (T-SAS). The application of the model to the Thailand floods in 2011 demonstrated that 80 % percent of the peak stream flow in mid-October was contributed by the precipitation water in the past three months, and that 35 % of downstream inundated water originated from the local precipitation over the floodplains. We also discussed the effects of dam reservoirs and upstream inundations on the water sources in the study area. The proposed approach is useful to understand the fundamental mechanism of large-scale flooding.

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The objective of this study is to investigate the relationship between flood concentration time and geograpgical and hydraulical characteristics by using a distributed hydrological model. The distributed model makes it possible to route the runoff generated over the whole catchment without any simplification. This model is applied to Uono river basin of 362km^2. The flood concentration time of Uono river basin itself and its 14 subbasins with different drainage areas are derived by driving the model with constant rainfall, 15mm/hr and 60mm/hr. Furthermore, this procedure is applied to virtual basins generated by digitally enlarging or shrinking above basin and subbasins. The flood concentration time of all these basins are plotted against geographical index and hydraulic index induced based on kinematic wave theory. Finally, a formula to estimate flood concentration time is proposed. It is shown that this formula represent the flood concentration time of Uono river basin and its 14 subbasins very well.

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The Kalman filter (KF) is a mathematical power tool that is used for real-time forecasting. In this paper, we implement KF on Urban Storage Function (USF) model which is a nonlinear lumped model considering urban runoff process. USF model using KF is applied to a virtual catchment where rainfall-runoff characteristics are known. The model parameters are updated with 1-minute river discharge data by KF. The characteristics of real-time forecasting of the model using KF is discussed by comparison with the model using a particle filter. The results show that KF forecasted in a very short computation time with performs comparable to the particle filter.

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This paper explores the effects of climatic characteristics on the shape of a flow duration curves (FDCs) in Japanese watersheds. We investigated the effects by correlation analyses between climatic characteristics and index flows in 14 Japanese watersheds, where we partitioned FDCs into three sections of exceedance probability (EP) : EP=0.0-0.3, 0.3-0.7 and 0.7-1.0. As the results, we found that the shapes of FDCs of the low probability section (EP=0.0-0.3) reflects the shapes of precipitation duration curves. Also, the shapes of FDCs of the intermediate probability section (EP=0.3-0.7) and the high probability section (EP=0.7-1.0) both showed strong correlations with seasonality index. Applying the above correlations, we estimated the shapes of FDCs in two different test watersheds and found that climatic characteristics alone are useful for roughly estimating the shapes of FDCs. Our findings indicate climatic characteristics are the primary factors that control the shapes of FDCs.

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Radioactive cesium (Cs-134 and Cs-137) dispersed from the Fukushima No.1 Nuclear Power Plant is strongly attached to surface soil layers. To estimate a movement of radioactive cesium with suspended sediment in a catchment scale, a distributed rainfall and sediment runoff model was developed. Radioactive cesium attached to suspended load was modeled by considering a sediment particle size distribution. A constructed simulation model reproduced an observed rainfall runoff as well as an estimation of sediment runoff considering the origin of the source of sediment generation and an estimation of the cesium movement contained in the suspended load.

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Modeling vegetation dynamics in a hydrological model is important considering the impacts of future change of terrestrial biomass under climate change on water resources management. In addition, regional vegetation dynamics is considered to affect local climate through land-atmosphere interaction. Therefore, we develop a distributed hydrological – dynamic vegetation coupling model that can calculate vegetation growth and death as a diagnosis valuable. This model, WEB-DHM + DVM is applied to the Medjerda river basin in North Africa. The simulated river discharge and leaf area index have a good agreement with the in-situ and satellite observations, respectively.

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To evaluate fertilization of the Mekong River flood and inundation, we observed nutrient concentrations of flood water and nutrient amounts of soil at paddy fields located in the Mekong River floodplain and calculated nutrient balance. We obtained the following conclusions; 1) Sluice gate is more effective system than rubber gate at the point of nutrients utilization because water at the level of a lower layer have much nutrients due to the deposition. 2) Nutrient balance calculation expresses that the amounts of nutrients contained in soil and inundation water are sufficient to provide for rice production. 3) The contribution ratio of flood to rice production that is presented in "the nutrients amount brought by inundation / the nutrients amount included in the harvested rice" are 98%, 50%, 88% and 17% about nitrate at Kandal, phosphorus at Kandal, nitrate at Takeo and phosphorus at Takeo respectively.

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This study aims at examining an availability of stormwater retention for pollutant runoff management and showing useful knowledge through simulations based upon monitoring data. A facility selected is a stormwater retention pond which is included in Moriyama River Water Treatment Facility located at Southern Lake Biwa basin. It has been operated in order to improve water quality which runs off into Lake Biwa by a series of facilities of a pre-treatment facility, a stormwater retention pond and a vegetation pond. Authors have monitored water quantity and quality into/out of the retention pond during storm events for four years, and developed a simulation model from the surveyed data. As a result of discussion on simulation results using the model, it was shown that stormwater retention had enough possibility to control pollutant runoff during storm events if correct operation was done. It was also shown that the simulation model was available for examining an optimal operation of the stormwater retention pond. These findings would leads to better environmental management of pollutant runoff.

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The distributed hydrological model WEB-DHM and the rice growth model SIMRIW-rainfed are coupled to grasp the required hydro-meteorological information for rain-fed agriculture. The results of the coupled model are validated by the LAI and soil moisture in the Sangker River Basin in western Cambodia. In this simulation, we targeted the dry season rice production in the rain-fed agricultural land so we assumed that they planted rice on 20 September 2011, referring the change of the LAI by MODIS. The sensitivity analysis showed that planting time has relatively higher sensitivity on crop yield than 10-day dry spell during the growing period. Irrigation or small rainfall (2mm/day) after heading until maturity was shown to increase yield. Thus, rainfall prediction at the beginning of the dry season is very important.

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A method for establishing stage-discharge curve (H-Q curve) using a runoff model to the rainfall observed in a basin and the water level observed in a river channel was discussed. A quadratic function that represented the relation between water level and discharge was built into the runoff model. When the observed water level hydrographs at some floods were reproduced, the H-Q curve was obtained. The method was applied to six water level stations in Shikoku which observed runoff quantity, and the established curve was compared with the H-Q curve based on the runoff observation. Two major findings were obtained: (1) a satisfied H-Q curve in which the error was 5-17% compared with measurement H-Q curve could be set up by using the data of one main flood event when there was a rain-gauge stations for each 30km2 in the basin or more; (2) a useful H-Q curve was still obtained by using a lot of flood events when the rain-gauge stations were sparse and were unevenly distributed.

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In recent years, the use of advanced delineation GIS data (ADGD) has become invaluable in studies that require accurate spatial distribution of land use. However, the preparation of ADGD, especially for urban catchment areas, is often tedious, time consuming and prone to errors, since these are mostly constructed manually using a digitized map. In this study, a computer algorithm (automated construction algorithm) was developed to automatically construct ADGD from a digitized 1:2500 topological map, using only geographical point features and geographic object boundaries that have land use attributes. A portion of the digitized map of the Kanda River basin was used to examine the accuracy of the newly developed algorithm. Evidences show that this algorithm can generate similar to more accurate geographical features when compared with the manual approach. The automated construction algorithm, thus, provide an accurate and efficient alternative in constructing ADGD, which can benefit future GIS-related studies.

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Soil water content and soil characteristics were measured in Shuangtai Wetland, which is one of National Nature Reserves in China and is also one of major places of reed production for paper industry. Continuous measurements of surface water level, soil water content and ground water level were carried out, and samples of soil layers containing fine roots of reed were analyzed. A vertical 1D numerical model was adopted for the simulation of vertical groundwater movement to understand the variation of soil water content obtained from the field measurement. Model parameters were determined based on the soil sample analysis and relating existing studies. The computational result had a fairly good agreement with the observation though uncertainties are still remained.

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Matsuyama in Ehime Prefecture has often experienced droughts and is one of the water-poorest cities in Japan. The purpose of this study is to analyze the effect of well pumping of groundwater on water resources of the watershed from 1950s to 2010s, using the datasets of groundwater level, river discharge, pumping from wells. The major findings are as follows. The groundwater level and river discharge decreased, while the average precipitation did not change in this term. The volume of water to 9 % of the precipitation in this watershed is pumped up from wells along Shigenobu River. WEP (water and energy transfer process) model, a distributed hydrologic model, shows that the well pumping brings the decrease of the groundwater level in the region from down to middle basin of the river. This agrees well with the fact that the drying up of the river is more extensively observed in recent years compared with that in 1950s.

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Groundwater observation wells have been bored in 40 sites in Tokyo Metropolis. Large fluctuations of unconfined and confined groundwater levels were observed after the 2011 off the Pacific coast of Tohoku earthquake at 98 observation wells in Tokyo. In this study, the characteristics of groundwater level fluctuation caused by the earthquake were evaluated using Self-Organizing Maps (SOM). The SOM has been suggested as a nonlinear classification method. As for the results, the SOM analysis succeeded in visualizing the characteristics of groundwater level fluctuation. Eight fluctuation patterns were identified for the characteristics of unconfined and confined groundwater level fluctuation. In addition, by comparing the results of the SOM with the visual inspection of fluctuation time series, it is shown that the SOM is successfully and objectively almost the same as the fluctuation patterns after the earthquake.

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To construct and conserve a tidal flat with biodiversity, it is necessary to understand the influence of subsurface groundwater discharge on the tidal flat environment. In this study, long and short term variations of groundwater in Ota River Delta are revealed based on groundwater level and quality data measured from 2002 to 2012. Moreover, the influence of delta groundwater on groundwater quality and the effect of steel sheet pile on groundwater circulation are also discussed. It was found that various subsurface environments were formed by different groundwater conditions. Further, the groundwater conditions were strongly varied by the construction of steel sheet pile.

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In this study, we investigated groundwater flow and its effects on the enhancement of water purification in a tidal flat located in the Ota River Floodway where a tide pool forms in the flood channel. It was found that groundwater flow from the flood channel maintained the groundwater level in the tidal flat, which contributes to both the relaxation of annual range groundwater temperature and the purification of groundwater quality. It is expected that, in the case that a low-water channel tidal flat forms in the river having compound structure, the nitrification and denitrification of sediment in the tidal flat are facilitated by constructing river structure to generate groundwater flow.

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In this study, column experiments were conducted to understand the release behavior of sediment from the sand columns. Further, a sediment filtration experiment was conducted under seepage flow with oscillating water head condition to investigate the permeability changes due to sediment migration. The results suggest that the permeability of the sand columns increased after making upward current, and increasing tendencies depended on the type of sediment. In addition, changes in piezo-metric head under seepage flow with oscillating water head condition could be simulated based on a conventional model with a relative error of 3%, leading to the prediction of decreases in porosity due to sediment retention. Therefore, changes in permeability of sand beds can be determined if the piezo-metric head is known.

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Arsenic (As) contamination of groundwater has become problem in the world. Although we know that anaerobic environments often promote arsenic release and mobilization from the solid phase, the precise mechanism remains unresolved because of complexity by the combination of several factors such as microbial activity and geochemical factors. In this study, two-dimensional transport model was developed for arsenic mobilization with microbiological redox mechanism. This model calculates the mass transport, bacteria mediated bio-chemical reducing processes, iron precipitation and Fe-As adsorption and desorption process in the three phases (BIO-, MOBILE- and MATRIX-PHASE). Results from a 2D-flow soil experiment were used to verify the simulation results of this model. This study showed the potential that this model could be more useful by evaluating issues such as interpretation of chemical evolving processes at field.

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Illegal waste disposal is a serious problem in Japan. The discarded waste may contain harmful pollutant. It penetrates into the ground by rain and can contaminate groundwater. If the contamination of groundwater due to illegal dumping occurs at the slope, the affected area can expand. However, previous studies principally focus on urban area and flat land. This study is made to clarify factors affecting pollutants flows. Factors we focused on are hydraulic conductivity and layer thickness of the slope. To this end, we perform a 3D numerical simulation of the subsurface advection and dispersion processes in the slope under periodic rainfall.

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The solute dispersivity is one of the most important factors to evaluate solute transport in groundwater environment. In this study, the non-destructive method to evaluate solute dispersivity by the thermal image of the thermal tracer test was proposed. Heated sodium chloride was used as tracer injected into the flow tank packed glass beads. Electrical conductivity and temperature change were observed at the 5 points of the downstream. According to the results of this experiment, thermal diffusivity of this system was evaluated. The thermal images were photographed at the tracer experiment under the same conditions. The method to evaluate solute dispersivity from this thermal image was examined. As a result of this study, it is possible to investigate solute dispersivity from the thermal image, if the thermal diffusivity of the medium is evaluated accurately.

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Conservative and sorptive transport simulations were conducted in heterogeneous aquifers to assess characteristics of macrodispersion. Heterogeneities in subsurface materials were represented as randomly correlated hydraulic conductivity and sorption partition coefficient fields. Transport computations were based upon a random walk particle tracking model linked with temporal and spatial moments. The simulations demonstrated that control plane and its middle element provide almost identical macrodispersivity estimates in terms of transverse mixing, but differ markedly from estimates of longitudinal mixing. The results also indicated that the increase of the physical or chemical heterogeneity provides the increase of the longitudinal and transverse macrodispersivities and affects late traveltimes of particles reaching a control plane, leading to the increase of the second-order temporal moment and relevant macrodispersion.

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To understand the characteristics and seasonal changes in flowing artesian wells in the Kurobe River alluvial fan (KRAF), the discharge, water quality, and isotope ratio of 23 flowing wells were observed for 18 months from March 2011. This paper newly reports the monthly discharge and water quality of these flowing wells. Variation in water flow at 10-minute intervals is also presented. All wells exhibited the same seasonal changes, and no spatial difference in water quality was found. Analysis of isotope ratios indicated that three wells located on the left bank of the KRAF were recharged from difference sources than the other wells that were recharged by the Kurobe River. Comparison with previous water quality measurements taken 10 to 20 years ago showed that the water quality had not changed. However, further research is needed to clarify long-term trends of the flowing water discharges.

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Multivariate statistical techniques, principal component and cluster analysis were applied to the data on groundwater quality of Limestone aquifer in the southern region of Okinawa, Japan, to extract principal factors corresponding to the different sources of variation in the hydrochemistry, with the objective of defining the main controls on the hydrochemistry at the regional scale. As a result of principal component analysis, ground water quality in the region could be classified into four principal components, that is, the groundwater is affected according to salt water and fertilizer (component 1), limestone dissolution (component 2), a redox state of a ground-water (component 3) and nitrogen accumulation/ denitrification (component 4). The cluster analysis was classified into four clusters according to the pollution situation of groundwater pollution in the study area, and the classification result was affected by season.

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