This study used rainfall and runoff records from Northern California watersheds with distinct wet and dry seasons to quantify dynamic storage changes during a rainy season based on a simple water balance analysis. Our findings suggested that the watersheds store significant amounts of rainfall with little corresponding runoff in the beginning of the wet season and then release considerably more water after they reach their storage capacities. The amount of rainfall required to fill the storages was the order of a few hundred millimeters (200-500 mm). According to the topographic analysis for each subwatershed, median gradients and maximum storage changes showed the positive correlation. We explained the observation findings with a hydrologically active bedrock hypothesis.

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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This paper reviews the consequences and implications of implementing structural flood mitigating measures in Metro Manila with respect to flood and environmental protection. It focuses particularly on the effects and consequences of constructing and operating structural flood mitigation measures to Metro Manila's vulnerability as caused by flood hazards. It is surmised that the structural flood mitigation measures are important components in the reduction of flood in Metro Manila, however, examination of its implementation has revealed, aside from the expected benefits, several disadvantages, which in some cases resulted in more damages and greater losses.

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This study aims at finding out present living condition of resettlers, about 40 years after construction of the Nam Ngum 1 dam in Laos. Field survey was carried out about two resettlement villages of Pakcheng and Phonhang. Pakcheng village and Phonhang village were established in 1968 and 1977 respectively for resettlers of Nam Ngum 1 dam. Survey was conducted on 50 households each in these villages. Those in Pakcheng village are much better off as compared with those in Phonhang village. Access to water and quality of road created the disparity between two villages. It is desirable that some corrective measures (e.g. improving road and provision of irrigation system) should be made for those in Phonhang village to resolve existing disparity.

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[in Japanese]

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In this study, availability of multi-objective utilization of the flood control system for non-point sources pollutant reduction is analyzed. The big tunnel stormwater storage system in the study river basin is under construction only for flood prevention. The storage of first-flush stormwater runoff is indicated to be effective for non-point source pollutant reduction, but restricted storage volume may bring flood risk. Some control strategies were proposed under perfect rainfall prediction, but prediction error has prevented application to real stormwater storage system. In this study, the optimal set-point control of stormwater storage system is estimated by a probabilistic analysis of the impact of flooding risk derived from the rainfall prediction error.

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Atmosphere-land surface interaction plays a dominant role on the hydrologic cycle. To get much deeper knowledge of hydrologic cycle, land surface hydrologic variables observed by satellite were analyzed. In this study, land surface hydrologic products derived from MODIS sensor, which have 6 km spatial resolution, are daily data sets and are available from 2001 to 2010, are used for time series analysis. Firstly, daily data is composited into 8-days data to remove unrealistic values even if daily product was already calibrated or corrected. It was found that there are spatial and temporal distribution of 10-years average and standard deviation for each 8-days term. The areas which have extreme interannual variability were pointed out from the analysis of standard score for each term.

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This study shows preliminary evaluation results of SMOS L2 soil moisture products of the validation site of JAXA in the Mongolian Plateau in 2010. As a result, SMOS will be probably able to observes soil moisture with the high measurement accuracy and the soil moisture products will be are useful.

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We investigated the leaf spectral reflectance and the chlorophyll concentration in a larch forest, Japan. The spectral reflectance and the chlorophyll concentration showed seasonal change. The change rate was large especially in spring and autumn. A linear relationship was obtained between leaf reflectance at wavelength of 500 nm and the chlorophyll concentration except the data of summer season. The summer data showed difference from the linear relationship. A similar characteristic was observed in the canopy scale by the spectroradiometer.

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[in Japanese]

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Thunderstorm or extreme rainfall causing flash flood characteristics are very important to understand and to characterize storms related to such flash flood. Those of characteristics include storm geometry, movement, speed, orientation, direction, recurrent interval, Intensity-Duration-Frequency (IDF) and regional frequency. Those analyses mainly have conducted by using observed rainfall acquired from dense rain gauge network or rainfall radar data. This research aims to characterizing storm severity of extreme rainfall caused flash flood. Considering a remote area or ungauge basin that lack of rainfall measurement, we use the geostationary satellite rainfall estimation to characterize those of storm severity.

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A plotting position formula assigns the probability of non-exceedance to the ranks of hydrological raw data. Since Cunnane reviewed and reorganized the formulae more than 30 years ago, many other studies have followed. None of them emerged as a definitive one, however, and today a number of plotting methods are used concurrently. Against this background, this paper reports on our examination of what constitutes a suitable plotting position formula for the Gumbel distribution, the log normal distribution and generalized extreme value distribution.

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[in Japanese]

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Specific discharge curves (flood envelope curves) in the Yoshii River Basin in Okayama Prefecture were estimated by applying depth-area-duration (DAD) analysis to radar-gauged rainfall data. Comparison of estimated discharge by the curves to discharge records, estimates well envelop not only record maximum specific discharges observed in Okayama Prefecture but also those in the Setouchi Region; however, discharges in small catchments tend to be overestimated by using these curves. This overestimation was explained by the fact that limited record maximum is not always real maximum for the catchments of the same area because of spatial distribution of maximum areal rainfall in the objective area.

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The Red River Delta (RRD) is one of two biggest deltas in Vietnam. The rapidly increasing amount of groundwater abstraction is mainly from shallow Pleistocene confined aquifers (PCA). Excessive groundwater exploitation without wise management has caused some serious problems. However, a fairly wide groundwater monitoring network in the Delta was not set up until 1995, and there has not yet been any analysis of variability of groundwater levels in the Delta due to the lack of available data. This paper investigated spatio-temporal variation of groundwater level (1995- 2009) in 63 wells for PCA in the delta.

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Due to a difficulty on a prerdiction of storm runoff responses from catchment properties without observations, a methodology on comparative hydrology for extracting runoff characteristics was applied to a headwater catchment (19km2) where rainfall was observed with a high spatial resoltion. The first step for the extraction was to separate effective rainfall from the obseration and the second was to analyze hyetograph-hydrograph conversion. Each step was represented by a simple model with a few parameters but was highly influenced by the rainfall resolution. This analysis demonstrates that comparisons of runoff characteristics among headwater catchments by a few parametrs play a key role in the storm runoff prediction besids the development of runoff models.

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[in Japanese]

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This paper aims to propose the lumped model of two-dimensional inundation flow in macro scale. This model ensures numerical compatibility with a basin-widely distributed runoff one in modeling accuracy and simplification. An inundating domain is divided into many infinitesimal elements constitutied of one straight and short channelin micro scale. Based on the Navier Stokes equations, the mass conservation and motion equations of inundating flow in this channel are successfully simplified. The resulting motion equation is in conformity with the Fourier's and the Darcy's Laws. It is lumped in macro scale with the other elements. It can be shown that the basic equation of inundating flow in macro scale is finally categorized in the group conformable to water-depth transfer phenomenon.

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The Tokyo Storm Runoff (TSR) model is applied for urban runoff analysis. The set-up of this TSR model is based on so-called urban landscape GIS delineation that faithfully describes the complicated urban land use features in detail. The TSR model was set up and evaluated for the Palmviken catchment in city of Arvika, Sweden. Modelling was performed using as inputs 60-minutes design storms with a return period of 10 years representing both today's and future climate. The future design storm generates more floods and also a bit upstream. It is possible that the additional flooding has a substantial impact depending on the type of buildings and activities in the flooded area.

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The incidence of heat disorders in July-August for Saitama prefecture were investigated in 2010. The incidence rate of heat disorders in Kumagaya was higher than in Saitama city. Sixty-five over ages occurred mainly in daily activities. Distribution of the daily maximum temperature on the day occurrence in the heat disorders in Saitama is lower than Kumagaya. Significant positive correlation was observed between the average incidence rate and daily maximum temperature. Distribution of the WBGT at daily maximum temperature on the day occurrence is also the same trend. In the results of multiple logistic models, significance was shown in the factor of WBGT at daily maximum temperature and population for 65 over ages.

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We constructed urban landscape GIS delineation of upper Kanda basin based on detailed distinction of land use division. In this study, we estimate the accurate ratio of permeable area of 100m-mesh land use division using advanced GIS data.

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[in Japanese]

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We developed a distributed water circulation model incorporating reservoir operation, and water allocation and management schemes for large irrigated paddy areas. The water allocation and management schemes are configured to account for water intake, allocation, and drainage of irrigated paddies. To apply these schemes, we categorized irrigated meshes into representative irrigation systems by exploiting the spatial database of irrigation facilities and beneficiary areas. The reservoir operation scheme is an algorithm used to determine the reservoir releases for irrigation to meet the requirement of downstream diversion weirs. We describe the integration of these schemes and discuss how the model facilitates evaluation of the interaction between hydrological cycle and irrigation systems.

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Tsunami caused by East Japan Earthquake broke drainage system of large paddy field area along Sendai Bay. Recovery of drainage system was the first priority problem. Based on field survey of damages, for reconstruction of rather strong drainage system, improvement of safety of drainage pumps and gates, pumping stations as tsunami shelter, emergency power supply system and use of canal along seashore are recommended. Furthermore, coastal tsunami risk area should not to be used as habitat areas but as agricultural land. These hazard buffer agricultural lands should allow tsunami inundation and designed and managed as hazard buffer area that can be equipped rapid salinity removing system.

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The weakening of vertical mixing in Lake Biwa is recently observed, and may have the reverse impact on water quality. It is necessary to understand the mechanism of vertical mixing. In this study, the three-dimension hydrodynamic model (water flow and temperature) for Lake Biwa was developed. This model was calculated for 1 year of 2007 by using the GPV data. The hydrodynamic model could generally represent three vortexes generating on the surface in summer season, and the vertical temperature distribution in each season. The vertical mixing arose in winter season by the sinking of low temperature water on the surface. In order to discuss the effect of the vertical mixing due to the climate warming, this model will be applied.

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Quantity and quality of exported coarse particulate organic matter was investigated in Nakatsugawa River, the second order stream in Saitama Prefecture during 5 flood events occurred between 2005 and 2008. Average drift density was ranged from 0.21 g m-3, 1.52 g m-3 and 2.84 g m-3 (dry weight) for winter, summer and autumn flood, respectively. Drift density was weakly correlated with discharge. However, lignin contents in leaf was higher in flood magnitude, and correlated with discharge. Based on the quality, exported CPOM was significantly different among the flood events as classified by the discriminant analysis. Flood timing and magnitude are highly affected the quantity and the quality of exported CPOM.

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Worldwide dams designed only for the purpose of flood mitigation have different definitions and classifications. In USA they are called Dry dam, in Austria flood retention basins, (Hochwasserruckhaltebecken in German), in Japan in stream flood controlam (Ryusuigata dam, Japanese), others Flood Mitigation Dam (FMD). It is one of good solutions in dam engineering for sustainable management of reservoirs, downstream river environment, and sediment transport. This paper summarizes history and present perspectives of these flood mitigation dams.

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Processes of extreme weather events must be reproduced in numerical atmospheric models to project their changes in a changing climate with. Then, we perform a set of the future projection experiments to quantitatively assess the future extreme weather changes using a super-high resolution atmospheric general circulation model and a cloud-resolving non-hydrostatic regional climate model under the SRES A1B scenario. At the end of the 21st century,surface wind speeds within a 200 km radius of the tropical cyclone center at land areas is projected to increase, and the 5-day precipitation total in Asia is projected to increase. The Baiu over Japan is modified due to a changing climate.

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Among disasters, hydrological disasters caused 87% of the global reported number of victims in 2010. Asia accounted for more than a third of the number of all reported disasters (CRED, 2011). Climate change is anticipated to worsen flood impacts as one of the reasons for the severity of the floods and thus it is needed to develop effective global flood risk assessment methodologies. The purpose of this study was to evaluate the spatial distribution of global flood risk using flood inundation level (FIL) and extreme scenario. FIL was estimated by using a model with a simplified geomorphologic algorithm. Extreme scenario was calculated the effects how the climate change impacts can affect flood area caused by extreme rainfall and discharge from present to end-of-the-21st century.

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This study analyses precipitation datasets derived by the super-high-resolution Atmospheric General Circulation Model (MRI-AGCM3.1S) and assesses the model ability to reproduce the global distribution of current droughts with the sense of probability assessment and the idea of unfixed time in length and season. The derived results are compared with 15 AOGCMs participated in CMIP3. Among all the 16 models, the comparison between the observed and the simulated data of the 20th century showed that MRI-AGCM3.1S fits best with observations in reproducibility of droughts. Global drought changes projection under A1B scenario is also assessed and the degree of agreement or confidence levels of drought severity is identified from ensemble analyses.

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In this study, future change of precipitation characteristic was examined using the multi-GCMs of CMIP3 (including 24 models) and MRI-AGCM (3.1S and 3.2S). The standard deviation of monthly precipitation and daily precipitation intensity in the top 2% were evaluated. The former is related to drought, the latter is related to flood. The result shows that both index would increase in the future, depending on the GCM.

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