The objective of this study is to investigate the effect of temporal resolution of hydrological data on canopy evaporation derived from an interception model taking into account of fractional vegetation cover. This newly developed model makes it possible to avoid a problem in our previous model which is based on the Rutter model. Hydrological data with different temporal resolution generated from a 28-year hourly hydrological data set is applied to this interception model. The effect is very significant and is quantified by a formula which relates the annual canopy evaporation with annual effective potential evaporation, canopy capacity and temporal resolution. Using this formula, true annual canopy evaporation invariant to temporal resolution can be derived from annual effective potential evaporation, canopy capacity and fractional vegetation cover. The concept of operational parameter value and its calculation algorithm are proposed. The operational parameter values corresponding to their true values and the temporal resolutions are computed to reproduce the true annual canopy evaporation. This implies the necessity to use operational parameter(s) according to temporal resolution of the data in the operation of hydrological models.

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Changes of the intensity and the frequency of extreme precipitation under climate change are great concerns to scientists and policy makers. We analyzed the 99th percentiles of 1-hour precipitation for each temperature bin based on the ground observational data. The result showed that, first: the 99th percentiles of 1-hour precipitation tend to increase exponentially with the rising temperature, second: the rate of the precipitation increase was almost same as the Clausius-Clapeyron like relation for most part of Japan, except that the rate was larger for lower latitude region, third : the 99th precipitation intensities tend to have a peak at higher temperature.

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Doppler lidar observation was conducted to investigate the statistical and structural characteristics of the atmospheric boundary layer (ABL) over urban area, Koganei, Tokyo, on 21 February 2010. Vertical distribution of the vertical velocity was measured at the height between 150 m to about 2,000 m from the ground with a constant interval of 76 m. The potential temperature (PT) profiles were also measured by radiosonde. Vertical velocity spectra in the ABL show two dominant time scales; one is about 15 minute, and the other is less than 5 minutes. The higher frequency motion extends up to the top of ABL determined by PT profiles, which would be attributed to the individual thermal plumes. The lower frequency motion penetrates into the capping inversion. This would be the contribution of the organized thermal cells which propagates into the capping inversion as gravity wave during daytime. Surface layer depth was estimated about 300 m. It is due to the enhanced mechanical production of turbulence in urban roughness.

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In this research, the convective behavior and the atmospheric heating processes over the Tibetan Plateau were investigated by using a land data assimilation system coupled with an atmospheric model (LDAS-A). LDAS-A directly assimilates the lower-frequency passive microwave brightness temperature and effectively improved the land surface hydrological variables. Firstly, this paper investigated the convective system movements by using the data sets derived from the LDAS-A and clarified their characteristic physical processes. Secondly, we quantitatively analyzed the components of the atmospheric heating based on the energy budget study, and showed that horizontal advection and adiabatic heating from the top of the troposphere play important roles as well as sensible and latent heat transfer through the boundary layer development and convections.

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The aim of this study is to reveal the dependency of turbulence structures on the types of surface geometry. The characteristics of the turbulence structures in the horizontal sections at the several measurement heights over the four types of surfaces, (1) Square Array, (2) Hight Variation, (3) 2D Canyon, (4) Flat surface, were investigated using Particle Image Velocimetry technique. Our attention mainly goes to the aspect ratio of turbulence structures, and they are quantitatively measured from the distributions of two-point correlation coefficients. The aspect ratios (streamwise length / spanwise width) of the structures, which were extracted using the threshold of Ruu=0.4, were found to be accurately parameterized by the shear strength at that height. The interesting result is that there is a critical value in the shear strength. The aspect ratio of turbulence structures is linearly increased with increasing shear strength until the critical value, and then the aspect ratio converges a constant value 7 : 2 regardless the magnitude of the velocity gradient.

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We investigated turbulent flow around building arrays of four different building aspect ratio (H/W) using large eddy simulation. This simulation was aimed to study the similarity of urban canopy flow and plant canopy flow which was expected with the increase of building aspect ratio. As aspect ratio increased, the streamwise flow speed within the urban canopy decreased. Drag coefficient of urban canopy increased with aspect ratio. This is probably due to the increase of frontal area index and the occurrence of transverse flow along the streets. According to quadrant analyses and turbulence statistics, momentum transfer became more efficient as aspect ratio increased. At a high aspect ratio, momentum was more effectively transferred at cross sections than gaps.

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Thermal boundary layers along the wall of a building were measured by using a thermocouple rake perpendicularly installed to the wall and a sonic anemometer with a high sampling frequency. In order to measure the temperature in the viscous layer, four thermocouples were set within 1mm from the wall surface. The Grashof number, Grx, which is a non-dimensional parameter of buoyant flows, was varied from 109 to 1012, to examine the scale effects. The boundary layer thickness normalized with similarity parameters for laminar natural convection was estimated, and the value is related to the fetch of heated wall. The measured temperature profiles were found to be composed of three layers. The layer closest to the wall is mainly controlled by the buoyancy flow due to heat from the wall, whereas in the farthest layer, the effects of the forced convection flows of the atmosphere become dominant. The middle layer is influenced by both the buoyancy flow and the forced convection flows.

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In order to investigate the mitigating effect of the thermal environment in the vicinity of the river and clarify thermal environment of urban area, the authors performed field observations in areas focusing on the Meguro and Arakawa River. From the results of field observation, following results are obtained; 1) There are two classes of air temperature distribution in the vicinity of the Meguro river based on the airy wind direction. 2) The air temperature above the Meguro River shows the lowest among of the observed lines. The maximum air temperature difference is 2 degrees and mitigating effect of thermal environments reaches about 70m from the river. 3) The maximum air temperature difference between the Arakawa river and surrounding areas is 5 degrees.

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We developed a new sensing technology for wind velocity and short/long wave radiation fluxes (Globe radio-anemometer). The technology is on the basis of the heat budget equations of three compact globe thermometers (GT), namely; a black GT (BGT), a white GT (WGT), and a black GT with a heat source inside (BGTH). The globe anemometer uses BGT and BGTH, and the globe radiometer does BGT and WGT. Three GTs used are 12 mm in diameter and 0.3 mm in thickness, much smaller than the standard GT. The root mean square of the error of the sensors were 0.24 m s^-1 for wind velocity, 21.3 W m^-2 for short wave radiation flux, and 12.3 W m^-2 for long wave radiation flux with 1-minute-averaged data.

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CReSiBUC consists of CReSS and SiBUC. This model is able to consider land surface conditions in detail. Especially, the characteristics of urban conditions such as artificial heat and geometry of building height can be considered. In this study, the effect of the physical-based downscaling is investigated by using CReSiBUC. Simulations are carried out around Tokyo Metropolitan Area during 5 summer seasons (from 2003 to 2007). Temperatures at 3 a.m. and Temperatures at 3 p.m. are investigated. It is found that outputs of CReSiBUC are more accurate than temperatures of MANAL. This result suggests the importance of considering urban conditions in detail.

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Thermal inertia is the square root of the product of volumetric heat capacity and thermal conductivity. Thermal inertia changes theoretically as the soil water content changes due to the large differences of the two parameters composing thermal inertia between dry soil and water. This study shows a method for retrieving thermal inertia from a heat budget model of the Earth surface incorporating radiative surface temperatures and meteorological data, and the retrieved thermal inertia correlated well with subsurface soil moisture. The analysis extended to difference of performance of the thermal inertia estimation according to the data frequency of surface temperature and meteorological data. Results show that data frequency corresponding to routine meteorological observations and the geostational satellite was enough to roughly discriminate thermal inertia estimates into a couple of ranks of soil moisture.

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In Cambodia, agriculture is the important industry which engages many people. However, the water supplied only during rainy season is the source of water for agriculture. To use the limited water resources effectively, it is necessary to apply the water-resource management based on the meteorological prediction and the river runoff prediction. As the factor of these predictions, the soil moisture plays a key role in water and thermal transportation to the atmosphere, and the contribution of river runoff property. On the other hand, the soil moisture distribution with the paddy field scale is helpful in the agricultural activity and management. Therefore, Synthetic Aperture Radars (SAR) is expected to observe soil moisture with high spatial resolution in large area. Recently, some multi-polarization SAR have been in operation. The purpose of this study is to develop the algorithm to estimate soil moisture by using multi-polarization data acquired with the Phased Array type L-band Synthetic Aperture Radar (PALSAR) onboard the Advanced Land Observing Satellite (ALOS).

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A distributed biosphere hydrological model, WEB-DHM, was applied to the semi-arid basin of the Medjerda River in Tunisia for simulation of soil moisture and groundwater variations. First, the model performance is checked and calibrated with daily observed river discharge. Second, satellite data from Gravity Recovery and Climate Experiment (GRACE) was extracted and checked by using the observed groundwater data. Then, the model applicability to soil moisture and groundwater simulation was validated by the GRACE data. Satellite-observed and simulated soil moisture and groundwater showed reasonable congruity as to their seasonal variation patterns, demonstrating the model’s potential for assessment of groundwater resources in semi-arid regions.

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Sprinkling management is indispensable for lawn-planting in greening urban areas. In this study, numerical experiments are performed using 1-D soil-plant-atmosphere continuum model in order to quantify the effect of sprinkling on the temperature distribution in four types of lawn covered soil. Obtained simulation results are investigated from the viewpoints of sprinkling efficiency, storage capacity of rainwater, and reduction effect of sensitive heat. They are summarized as follows, 1) Suitable sprinkling plan should be chosen according to the soil hydraulic properties and the drainage condition. 2) Optimum sprinkling level can be estimated based on the maximum effective soil moisture and the sprinkling control condition. 3) Maintenance of high heat conductivity of the surface soil by controlling soil moisture proved to be effective for the improvement of heat environment.

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The present study explored physiographic watershed conditions which increase droughty flow in Japanese mountainous watersheds toward the mapping of ground water recharge potential, assuming that higher droughty flow originates higher water recharge potential. The results suggested that a highly elevated watershed underlain by Quaternary rocks, covered by Andosol or farm lands tends to generate higher droughty flow and hence has a higher ground water recharge potential. Then we defined the sum of the satisfied conditions listed above as the "ground water recharge potential index" and mapped it to verify the geographic distribution of the index. Comparison with the geographic distribution of "mega-springs" that generates more than 1.0 m³/s exhibited our ground water recharge potential map is acceptable to some degree.

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In the last 60 years, huge-scale irrigation project has been carried out and this project has occurred serious water scarcity in the Aral Sea Basin. The Aral Sea has shrunk to 10% of 1960’s level and a lot of people are suffering from serious water scarcity. To solve the problem, sustainable irrigation plan is required. For the plan, quantity of water resources and the impact of global warming must be simulated. In this study, annual water and heat balance in the Aral Sea Basin is analyzed from 1961 to 2003 by SiBUC. SiBUC is one of the land surface models which can analyze water for irrigation in physical way. Water balance in this basin is reproduced in the past and the impacts of expanding irrigated area to water balance in this basin are analyzed.

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Unusual weather, such as urban localized heavy rain, has become a serious problem lately due to the disasters caused by it. In this work, the latest data of Tokyo, Japan is used with past ones to see the dramatic change in urban geometry and to understand the spatial anomaly of concentrated heavy rain in summer time. As a result, the urban geometry in Tokyo has indeed grown. Adding the displacement height to actual elevation gives the "affective" elevation, which is very low along the bay and abruptly increases as it approaches the western areas. This sudden increase in elevation seems to correspond with where the anomaly of rainfall for concentrated heavy rain becomes positive. In addition, the 9-year data from the River Bureau shows the shift of positive anomaly into the urban area. Finally, the spatial deviation, driven by the Amesh data, indicates the strong relationship between urbanization and precipitation in Tokyo.

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This paper describes an assimilation method to modify underestimation of spatial snowfall distribution. In the Yoneshiro River catchment, underestimation of spatial snowfall distribution causes less river discharge in a runoff model. Error of observed precipitation has a great influence on accuracy of snowfall distribution, especially, on condition of heavier snowfall. In order to reduce the observation error, the snowmelt-runoff model incorporates assimilation strategy of observed snow depth into snow water equivalent (SWE) model at regular intervals. As results, the assimilation makes an improvement in the accuracy of the snowmelt-runoff simulation that the Nash-Sutcliffe coefficient is changed from 0.32 to 0.93.

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This paper describes the acidity and main ion concentration of snowfall, snowpack and snowmelt water in the temperate snow area. In order to understand the variation of snow water quality and its relationship among snow, snowpack and snowmelt, snow monitoring and chemical measurement were conducted from December 2008 to March 2009 at Tohkamachi experiment site. As a result, the both of snowfall and snowmelt were high acidity and their average were around 4.6 and 5.0, individually. However, high frequencies of rainfall and snowmelt occurrence during winter decrease the high acidity of snowpack and snowmelt water since they prevent the chemical matter from depositing in the snowpack layer. Moreover, it is suspected that the soil component from Eurasia continent contained in the snow particle also decrease the high acidity of snowfall and snowpack.

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This study aims to reproduce the water temperature structure in the Imja glacial lake using the 3D-Hydrodynamic model "Imja-3D" and the hypothetic meteorological datasets at the Imja glacial lake. The one-year datasets of hourly average air temperature were hypothesized using the temperature datasets at Namche Bazaar in 2008. The datasets of the wind speeds and the wind directions were considered diurnal pattern of the regional climate features in the Solukhumbu region. The model reproduced the water temperature structure of the lake in July 2008. The thermocline appeared near the lake water surface. The water temperature (2-3 degree) distribution was shown in mid layer. These results showed the similar water temperature structure on the observed one in the Imja glacial lake in 1997.

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To clarify the water balance of the melting snow period, we estimated the snow water equivalent from spatial snow distribution using a high resolution digital elevation model (DEM). The paper built a model to estimate a snow water equivalent using the spatial snow distribution provided from an airborne laser altimetry of the snow peak obtained in the Jozankei Dam basin in Sapporo. In addition, we estimated the secular variation of the snow water equivalent by incorporating snow depth and snow surveys observed by a dam in a model.As a result of analysis, the presumed precision included an error of 20% compared with the average snowmelt rate found from the water balance. Additionally, the adaptability of the model as a method to confirm snow surveys was confirmed.

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We developed a snow retrieval algorithm which is capable to estimate the snow quantity from the satellite microwave data (Tsutsui et. al.; 2007). However it has various problems in order to estimate the high-accuracy global snow depth yet. : 1) Occurrence of the time-oriented fluctuation in the estimated snow depth, 2) Underestimation of snow depth in heavy-snow region, 3) Erroneous estimation of snow depth in the snow free region. In this study, this snow retrieval algorithm was improved about these problems. Furthermore the effectiveness of improvement was verified in the GTS ground-based 111 stations. In the result, the estimated snow depth was in relatively good agreement with the in situ data.

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We analyzed results of three Regional Climate Models (RCMs) for 1984 to 2004 performed at 20-km horizontal grid spacing over Japan and the results of Japanese reanalysis data (JRA), and compared them with ground observations. Although JRA underestimated precipitation in Kochi Prefecture in the summer and in Niigata Prefecture in the winter, all the RCMs improved the underestimated precipitation in both prefectures. In addition, the skills of interannual variations in the three RCMs are superior to those in JRA. Futhermore, the skills of multi-model ensemble means, in particular, weighted multi-model ensemble means are distinctly superior to those of JRA on an interannual timescale. Thus, RCMs and their multi-model ensemble means are powerful tools for investigating interannual variations of future projections and seasonal predictions over Japan.

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To improve water vapor and cloud liquid water content in a numerical weather prediction model, Cloud Microphysics Data Assimilation System CMDAS) was developed. CMDAS improves an atmospheric condition by assimilating the brightness temperature data observed by the Advanced Microwave Scanning Radiometer for Earth Observing System (AMSR-E). In the optimization scheme of CMDAS, a number of combinations of integrated water vapor and cloud water content are firstly given and those integrated values are vertically distributed depending on cloud top height (CTH). Using those vertical profiles, CMDAS searches the optimal atmospheric condition through a model operator and an observation operator. In the original CMDAS, a constant value is used as CTH. In this study, a horizontal distribution of CTH estimated from Multi-functional Transport Satellite (MTSAT)observation is applied to CMDAS and the effects of CTH information which is temporally and spatially consistent are examined.

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   Satellite-based rainfall data such as GSMaP are expected to be adapted to flood forecasting in ungauged basins since they can be obtained world-wide in near real-time for free. However, GSMaP is often underestimated comparing with ground gauged precipitation, which poses a problem in applying the product to flood management. To solve this problem, Shiraishi et al. developed GSMaP correction method based on its movement of rainfall area and successfully reduced the error rate in a Japanese river basin.
   In this study, the GSMaP correction method was applied to typhoon Morakot in Kaoping River Basin and the entire Taiwan. The results showed that the correction formula for the Yoshinogawa River Basin can be applied to the Kaoping River Basin because of the similar basin scale and rainfall type and it cannot be applied to the entire Taiwan because of the much larger basin scale.
   What is more, the influence of the frequency of microwave radiometer observations on the accuracy of corrected GSMaP was validated and the outcome implied the importance of the elapsed time of microwave radiometer observation as a reliability indicator for corrected GSMaP_NRT used in flood forecasting systems.

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We investigated the diurnal rainfall variation in Matsuyama plain using datasets from AMeDAS, MLIT, and local government. The evening maximum precipitation is especially remarkable in the inland region and along a river. It is known that a river is street of wind for land and sea breezes. Sea breeze would contribute to an increase in the water vapor content over inland regions through the moist air advection from coastal regions. During the period of 1980-2009, the time when the morning maximum precipitation appears shift two hours later every ten years. Similarly, the offshore land breeze is getting more significant at the rate of 200 ms-1h every ten years.

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The Z-R relationship (Z=aR^b) between radar reflectivity factor Z and precipitation rate R has been used for operational radar measurements, but its coefficients (a, b) are known to be highly variable in time and space and also dependent on precipitation types. The Dual-frequency Precipitation Radar (DPR) is expected to instantaneously estimate the 2-moment drop size distribution (DSD) function and to finally derive global maps of (a, b). For this big goal, it is necessary to improve the accuracy of the instantaneous dual-frequency retrieval method. In this study, Mardiana’s method (MA04) is tested with a simulated DPR measurement dataset, and it is found that MA04 has negative bias which corresponds to 40% of the true precipitation rate. While the true equivalent radar reflectivity factor Z_e does not change largely along the range, the estimates of Z_e by MA04 tend to be smaller at lower range bins. MA04 is modified into three new methods. In the best method, the bias is limited to 18% of the truth.

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Characteristics of the post-monsoon rainfalls in Cambodia are examined through the combined use of NCEP-FNL global reanalysis data and the in-situ raingauge and AWS data. In the western Cambodia, rainfall still occurs during one month after the withdrawal of the Asian summer monsoon. About 30~40% of which was revealed to be brought by the redistribution of water vapor over Cambodia by the local atmospheric circulation. This rainfall occurs only under the period when there exists enough precipitable water. Decrease of precipitable water in China at late November reduces water vapor over Cambodia, resulting in disappearance of the locally-produced rainfall after this period. In addition, even when enough precipitable water exists, if the nighttime land-breeze at the southwest of the lake or the northeast winter monsoon is too weak, it doesn’t rain. Too strong winter monsoon is also unfavorable for local rainfall.

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Statistical approaches for correcting bias in general circulation model’s monthly precipitation are compared. We evaluate the methods by focusing on the average and variance of the bias-corrected data. For average, the difference of results between methods is small. For variance, on the other hand, the difference is not small. The characteristics of bias corrected data are also compared between methods and between GCM outputs. The methods that correct the bias better in the retrospective period tend to reduce the differences of projection between GCM outputs. The methods are applied to the outputs of MIROC5, and their bias corrected data is analyzed in this study.

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The predictability of the heavy rainfall disaster at Kani City, Japan in July 2010 is investigated using a model ensemble approach which relies on the combination of 32 member ensembles obtained from multiple parameterizations in the mesoscale meteorological model PSU/NCAR MM5. The model is initialized using the 20-km resolution global analyses JMA GSM-GPV with and without the radar-data assimilation system developed by Yoshino et al. (2009). It is found that the multi-parameterization ensemble forecasts averaged by 32 members during 24 hours are very skillful in indicating the area of severe local storm activity, while each member deviates largely from the ensemble mean. Furthermore, the radar-assimilated ensemble forecasts enable us to more precisely predict the area of greatest rainfall potential, because the initial conditions used here realistically represent 3-dimensional distributions of cloud microphysical properties in the atmosphere.

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Various problems concerning the global environment such as climate change, urbanization, and the heat island phenomenon are paid to attention, especially in terms of rainfall characteristics. This paper focused on characteristics of diurnal patterns of rainfall at Tokyo (Ohtemachi) based on 120-years hourly data from 1890 to 2008. Diurnal patterns were analyzed by using the "P/D" diagnostics which indicates the shape of a single rainfall event by the peak rainfall amount and its duration (whole duration). The P/D diagnostics showed the intensification of short-time rainfall amount in recent. In addition, we proposed a new "P/D" diagnostics which indicates the shape of a single rainfall event with the peak rainfall amount and its duration (from the starting time to the peak time). The results we obtained are following. 1) There is an increasing tendency in the short-time afternoon rainfall. 2) The duration to reaching peak amount for each single rainfall event is clearly decreased particularly at 15LST and 19LST in the recent two decades.

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It has been reported that the appearance of Tapering Cloud (TC) is one of the most disastrous cloud systems causing heavy rainfall and associated serious disasters. However, there are only a few reports that robustly analyzed the TC due to high frequency of TCs formed in the ocean. Therefore, paying attention to easily recognizable triangle shape of TCs seen in infrared satellite images, our study extracted TCs in the Japan islands and its surroundings for 11 years (Jun-Sep: 1999-2009) , and investigated significant relationships between TCs and heavy rainfall disasters. The results show that remarkably-disastrous events were closely related to the activity of TCs regardless of low frequency of TCs that caused heavy rainfall disasters in the Japan Islands. In these events, some TCs could be detected in advance before heavy rainfall disasters occurred. Therefore, it can be expected that the behavior of TCs is available as valuable information for detecting a precursor of heavy rainfall.

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Torrential rainfall events often brought sudden flood and damages especially in urban area. However, it is still hard to forecast the occurrence of torrential rainfall. In this study we analyzed evolution process of a torrential rainfall event that was occurred at Itabashi, Tokyo, on July 5, 2010, to accumulate knowledge of developing mechanism and possibility of forecast of this type of rainfall. The regional meteorological model, WRF (Weather Research and Forecasting), reproduced the torrential rainfall event fairly well by the use of JMA-MSM (Japan Meteorological Agency-Mesoscale Model) data as initial and boundary conditions. For the development and maintenance of the rainfall, three streams of see-breezes from Sagami bay/ Tokyo bay/ Kashima Nada played a key role in accumulating moisture and supplying it into the precipitating system. The model reproduced the sea-breezes well, that is why it could reproduce the rainfall well.

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Precipitation analysis for heavy rainfalls in Tokai district on September 11-12, 2000 and August 28-29, 2008 was performed based on 10-minute precipitation data. Rainfall distribution analyses showed that a rain band in the direction of the prevailing wind at middle levels slowly moved eastward on the western Aichi Prefecture throughout the both events. The rain band consisted of aligned heavy-rain cells of about 5-10 km diameter that traveled successively along the rain band. The band lay 10-20 km toward the cold sector of a meso-scale convergence line. Moreover, an analysis of 10-minute precipitation data for the past 22 years revealed that the areas including the northern Chita Peninsula and Nagoya City have a maximum frequency of heavy rain of short duration despite having the lowest annual total precipitation in Aichi Prefecture. Thus, these areas seem to have topographic characters favoring concentrated heavy rainfall only under specific meteorological conditions.

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"Guerilla heavy rainfall" is a newly-coined word by mass media of Japan. The four major newspaper publishing companies began to use this word frequently from the beginning of August, 2008. The definition of "Guerilla heavy rainfall" is not clear. It was found from the result of newspaper article analysis from 2008 to 2009 that short-time very heavy rainfall events are called "Guerilla heavy rainfall". In this study, the rainfall event of 80mm or more of rainfalls of 1 hour and 149mm or less of rainfalls was defined as "Guerilla heavy rainfall". 104 events of "Guerilla heavy rainfall" were extracted from AMeDAS precipitation data from 1979 to 2008. There were two victims of these heavy rainfall events in total. They killed at basement or underpass. Although inundation above the floor level occurred in 38% of event, the damage of 100 or more buildings was 9%. We may say that "Guerilla heavy rainfall" does not cause large-scale damage. However, it is necessary to keep in mind that damage caused by "Guerilla heavy rainfall" is generated well in high-risk area of flood, such as basement, underpass, low land and river park.

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A real-time river stage forecasting method is developed, which is aimed to apply to river sections where a rating curve does not exist. The method uses a particle filter combined with the dynamic wave model. A number of the dynamic wave models (particles) which have different parameter values and boundary conditions run in parallel; a set of well behaved particles are selected in real time according to the observed river stage; and several hours-ahead river stages are predicted with their prediction error at each observation time step. The method is applied to the Katsura River for the flood of the typhoon No. 23 in 2004. The predicted river stage shows a good agreement with the observed one. The predicted maximum river stages along the study river section also well explain the flood marks.

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Tokyo Storm Runoff (TSR) model using urban landscape GIS delineation is proposed. The polygon feature GIS data are used to parameterize complicated land use patterns in the urban catchment for the modelling. It is shown how various land use, streets, drainage and river systems are used as input to coupled hydraulic and hydrological models. In this model, if the precipitation rate and surface runoff rate from adjacent elements exceed the infiltration rate, runoff will occur. The model is applied to a flood-prone urban catchment in Tokyo with hypothetical rainfall events. It is found that the model can simulate the physical rainfall-runoff process, but validation of the effects of infiltration process expressed in this study should be done in the future.

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Using a runoff system composed of a hillslope runoff generation model and a channel network, this paper derives theoretical differential equations to calculate the first- to third-order central moments of discharge. Numerical simulation shows the results of cross-checking the validity of the derived equations. The results are as follows: σ_qi² and μ_qi3 , in a steady state are regarded as constant when the catchment area is smaller than one hundred and several tens kilometers square. The results of this study can be applicable to the evaluation method of lumping process of models based on their stochastic response characteristics.

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Flood inundation caused by cyclone Nargis is simulated on the Irrawaddy delta with a newly developed two-dimensional rainfall-runoff-inundation model. The primary objective of the model is to provide useful information for emergency responses during or at immediately after flood disasters. This study applies the model to simulate the storm surge flooding with the boundary condition of surge water level at the coastal line. The simulated result was compared with an inundation map produced by remote sensing. The reasonable agreement between the simulated and the remotely sensed inundation map confirmed the model reproducibility for storm surge inundations at the large areas. The simulation shows also the importance for considering rainfall-runoff processes for adequate inundation simulations.

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Efficient flood control by a dam requires proper understanding of the basin storage capacity (BSC) in upstream area, because flood runoff depends on the water content there. Using a long-term water cycle model, this paper estimates the BSC to be used for flood control. Two methods (1) the runoff percentage calculation and (2) the BSC-based minimum dam water level that secures the necessary water supply are proposed and applied to the flooding events with different basin conditions (wet/dry). The application results suggest that the BSC obtained from the long-term water balance is useful for effective flood control by a dam.

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Real-time flood forecasting needs accurate rainfall forecast, because Japanese river basins have a small area and steep topography that cause rapid rainfall-runoff. This paper aims to improve the accuracy of flood forecasting, considering recent advancement of short-term rainfall forecasts provided from the Japan Meteorological Agency (JMA). The method proposed here is to combine predictions by the Meso Scale Model with other predictions such as the Precipitation Nowcast and the Very Short Range Forecast. The results of its application to the Okawa River basin in Miyagi Prefecture indicate improvement in flood forecasting accuracy. Since this method is easy-to-use and effective, it would be useful for the improvement of flood forecasting in other river basins in Japan.

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Kushiro wetland located in the eastern part of Hokkaido was registered by Ramsar Treaty in 1980, and was registered as a national park in Japan in 1987. The previous studies reveal that the area of alders have been expanding, which results in the decrease in the wetland area in the past 30 years. It is demonstrated that the increase in alders is due to the accumulation of sediment and the increase in nutrient in the wetland. However, the mechanisms, which control sedimentation and nutrient transport, have not been clarified. Therefore, this study aims to understand the mechanism of water circulation in Kushiro wetland by using distributed hydrological model from the comparisons between 2003 and 1970s. As a result, rainfall pattern is found to change which leads to in the increase in discharge from 1970s to 2003.

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It is well known that since agricultural water withdrawal has much affect on water circulation system, accurate analysis of river discharge or water balance are difficult with less regard for it. In this study, water circulation model composed of land surface model and distributed runoff model is proposed at 10km 10km resolution. In this model, irrigation water, which is estimated with land surface model, is introduced to river discharge analysis. The model is applied to the Chao Phraya River in Thailand, and reproduced seasonal water balance. Additionally, the discharge on dry season simulated with the model is improved as a result of including irrigation. Since the model, which is basically developed from global data sets, simulated seasonal change of river discharge, it can be suggested that our model has university to other river basins.

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A special method for estimating river discharges, using rainfall data in and around a catchment and water level data in a river, was applied to the Sayo River flood event in 2009, and the peak discharge and flood hydrograph were estimated. The method was designed for situations where the river’s water level was measured but the discharge not measured, as in Sayo River. A catchment runoff model was used to assist in establishing a level-discharge rating curve. As a result, the water level hydrograph at Sayo station was able to be reproduced successfully. The rating curve (H-Q curve) was well set up. The flood discharge at the embankment crest level was estimated to be about 910m3/s. By using the runoff model, the amount of rainwater storage in the basin in this flood event was estimated to be 35mm. Also the storage capacity in the surface horizon was very small (about 10% of all capacity).

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Physically distributed modeling is highly required for hydrological prediction in watersheds with heterogeneous land surfaces, soils and aquifers under uneven distribution of rainfall to better estimate impacts of future environmental changes such as land cover alterations and climate change. In this study, the applicability of WEP model, a grid-based distributed hydrological model, was enhanced by focusing on the hydrological influence of soil types, geological condition, land use, and their spatial distributions. The methodology to consider these factors in model inputs is established with the use of dataset of soil properties and geological conditions of the Abukuma river watershed. Simulation results showed good agreements with observed for most sub-watersheds followed by a certain parameter calibration, suggesting the potentially high applicability to a variety of watershed conditions.

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This study conducted runoff analysis for the floods in Sep. 1954 and Oct. 2004 by the distributed runoff model for Yanase Dam basin in the upper Douzangawa River, where once become devastated by an operation of Besshi copper mine and recovered by afforestation and tree species conversion. Subsequently, a relationship between the tree species conversion over 50 years and changes of flood runoff characteristics, and a reduction effect of forest in peak discharge of flood were examined.As a conclusion, authors presumed approximately 20 percent improvement of the peak discharge reduction by tree species conversion. It was supposed that the difference of flood runoff characteristic were explained by parameters in relation to rainfall interception and evaporation function of forest, and in Yanase Dam basin, the change of tree density sensitively influenced on runoff characteristics.

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The main purpose of this study is to develop a new design method for the retaining wall in a cold district. In the cold district, snowfall and snowmelt is one of the main factors in sediment related disaster. However, the effect of the snowmelt is not being taken account of sediment disasters precaution and evacuation system. In this study, we target at past slope failure disaster and quantitatively evaluate that the effect of rainfall and snowmelt on groundwater level and then verify the stability of slope. Water supplied on the slope was determined from the probabilistic approach of the snowmelt using DegreeDay method in this study. Furthermore, a slope stability analysis was carried out based on the ground water level that was obtained from the unsaturated infiltration flow with the saturated seepage flow simulations. From the result of the slope stability analysis, it was found that the effect of ground water level on the stability of slope is much bigger than that of other factors.

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Groundwater pollution by nitrate due to agricultural activities has become serious environmental issues in the two shirasu plateaus of Kasanohara and Kanoyabaru of Osumi peninsula, Kagoshima prefecture. We developed a groundwater recharge model and examined the water budget characteristics. Furthermore, two-dimensional numerical simulations were carried out to evaluate the effects of countermeasures for the contaminated source. The results of water balance analysis showed that runoff is 10-15%, groundwater recharge is 65%, and evapotranspiration is 20-25% of precipitation in the catchment area. The numerical results indicate that it takes 50 years for Kasanohara and 80 years for Kanoyabaru to display the effects of countermeasure of 80% reduction in concentration of the source zone. The long-term numerical simulation suggested that detailed recharge rate fluctuation rather than constant recharge rate should be applied.

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Submarine Groundwater Discharge (SGD) is now recognized as a significant role to the ecology of coastal environment as well as river discharge. This paper takes a first step for highlighting nutrient transport through SGD to volcanic rock area along the Ariake Bay. SGD rates and their qualities along the coastal area of the Ariake Bay, Ohura, Saga Prefecture, Kawachi, Kumamoto Prefecture, and Fukae, Nagasaki Prefecture regions are investigated. As a result, SGD generally decreased with the distance from the shoreline except Ohura point where large seepage rate is observed. It is presumed that SGD could be classified into two types based on the rate of SGD and the geological structure. Then, it is indicated that the SGD oxidation-reduction condition varied with seepage rate and path way. The results of this study demonstrate that SGD may be considered as a significant source of nutrient to the coastal area in Ariake Bay.

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Knowledge of seawater intrusion to aquifer is very important for the efficient use of groundwater in coastal area. Conventional numerical simulation for seawater intrusion was mainly performed in uniform porous media. However it is known that hydraulic conductivity varies spatially. The objective of this paper is to investigate a seawater intrusion behavior in non-uniform porous media by numerical simulation using the spatial distribution model for hydraulic conductivity. The results show that the length of seawater intrusion is affected by the shape of permeability distribution. When the aquifer has laminar structure of permeability, the change of seawater intrusion length is smaller than the general aquifer.

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