Since Pakistan locates in the west edge of the Asian Summer Monsoon Region, the amount of precipitation is severely influenced by the variability of monsoon activity. To reduce the damage of these water hazards, this research aims to show one reason of the difference in predicting precipitation in Pakistan, which is still a very challenging problem due to the complicated mechanism of the monsoon system. As a first step, we examine the strong influence of the local Hadley Circulation over Arabian Sea on the monsoonal precipitation activity in Pakistan. Madden-Julian Oscillation (MJO)-Phase composite analysis clarifies the temporal variation of the strength of the local Hadley Circulation is closely related to the eastward propagation of MJO. Finally, the analysis on the seasonal forecasting data of GCM MIROC confirmed that the MJO takes a great role in forcing the intra-seasonal variability of Local Hadley Circulation. As a result, it is indicated that the fail to reproduce the MJO can be one of the great causalities of the fail in correct seasonal prediction.

抄録全体を表示

We developed a simple climate model, and investigated the ability of the simple climate model to emulate global mean surface air temperature (SAT) changes of an atmosphere-ocean general circulation models (MIROC5) in representative concentration pathways (RCPs). Some previous research indicated that climate sensitivity, ocean vertical diffusion and anthropogenic aerosol forcings (direct and indirect effects of sulfate aerosol, black carbon and organic carbon) are essentially important factors to emulate global mean SAT changes of Atmosphere-ocean general circulation models. We, therefore, estimate these important parameters in the simple climate model using a Metropolis-Hastings Markov chain Monte Carlo (MCMC) approach. As a result, our simple climate model can successfully emulate global mean SAT changes of MIROC5 in RCPs with the estimated parameters by the MCMC approach.

抄録全体を表示

Chao Phraya river basin is one of the largest basins in the Indochina Peninsula where is located at the South East Asian monsoon region. This study focuses on the diurnal patterns of several cloud types in the rainy season especially during June to August. We used MTSAT (Multi-functional Transport Satellite) Infra-red information from which we classified the clouds into 7 types and then analyzed diurnal characteristics of each cloud type especially in the years 2010 and 2011. 2010 was a drought year and clouds appeared earlier than in the climatology (1996-2011) and 2011, on the other hand, was a flood year and clouds appeared approximately 1 hour later than in the climatology. We obtained results which showed all types of clouds had each diurnal pattern of appearance. Furthermore, those patterns were similar between 2010 and 2011, however they shifted a few hours earlier in 2011 than in 2010.

抄録全体を表示

In this study, an evapotranspiration model that can express the amount of evapotranspiration accounting for differences in soil moisture and penetration characteristics of individual land-surface features is proposed. The model is composed of two components; the infiltration area model based on SMPT model to represent the infiltration process of the surface soil, and the impervious area model considering depression storage in impervious areas. Furthermore, the infiltration area model takes into account the state of the soil moisture and differences in land use of the land-surface features, and estimates the latent and sensible heat using a heat balance equation based on the bulk formula. The model was applied to the highly urbanized upstream basin of Kanda River, and the impacts of differences in land use on the spatial distribution of evapotranspiration and land surface temperature was analyzed.

抄録全体を表示

Horizontal turbulent flow fields within atmospheric boundary layer above an urban area (Tokyo, Japan) measured by Doppler lidar in autumn and winter were visually classified into six groups, Streak, No streak, Mixed, Fish net, Front, The others. The conditions of each flow occurrence were examined with observed surface meteorological data and related scaling parameters. The following results were obtained: (1)Streak dominates 64% of all valid data, while Fish net does only 2%. No streak and The others, look more laminar rather than turbulent, reach to 20% contribution in total. (2) Each flow patterns can be categorized by . and Re ( is boundary layer height, is the Monin Obukhov length. Re is Reynolds number, the length scale of which is .). (3) Each flow patterns can be categorized by . and Resurf (z is observation height. Resurf is Reynolds number, the length scale of which is .) as well as . and Re. (4) The diagrams of . and Re, and . and Resurf qualitatively illustrate the flow regimes.

抄録全体を表示

Numerical weather prediction models for urban weather require various urban parameters such as urban geometry and anthropogenic heat emission. Preparing databases of these urban parameters is essential for better reproducibility of urban weather simulation.
In this paper, a database of urban geometric parameters for the whole Japan is created using a detailed building GIS. This database includes average, maximum, and standard deviation of building heights, plane and frontal area indices, roughness length for momentum, displacement height, and sky view factor. Furthermore, to expand this database to areas where detailed building GIS is not well prepared, methods of estimating the surface parameters are proposed. These methods require only a global digital elevation models and aerial imagery, which are now open to public inspection and easy to obtain. The results are compared with values derived from high-resolution building heights data.

抄録全体を表示

We verified the validity of the downward longwave radiation equation by Kondo et al.(1991) using the high-accurate BSRN radiation data observed at the five meteorological stations in Japan. The following facts were noted. 1)The original downward longwave radiation equation shows a root mean square error of 8.8 W/m2 at the five BSRN stations and tends to underestimate all the year round at the Tateno station. 2)The downward longwave radiation equation with recalibrated parameters gives a root mean square error of 8.3 W/m2. 3)Because the recalibration effect is limited, it is likely that parameters of the original longwave radiation equation are widely applicable except a winter season at Tateno station.

抄録全体を表示

The present study investigates the statistical features of a 110-year annual mean total water storage index (ATWSI) in a 3-layer tank model in Japan. The total water storage index, which is the summation of water storage in the three tanks, was obtained by running the 3-layer tank model forced with gridded daily precipitation data for a 110-year period from 1900 to 2009. The climatological ATWSI is 23 mm, and the maximum and minimum values are 41 and 3 mm, respectively. The climatological ATWSI resembles the climatological annual mean precipitation spatially, and features of the climatological ATWSI are also seen in the climatological annual mean water storage of each tank. The Japan-area-mean ATWSI decreases by 0.8 mm/100 year without statistical significance. The 5-year mean ATWSI shows one to two decadal variations, but has different spatial patterns even when the same sign phase occurs. This suggests that the decadal variations of the ATWSI could be caused by different climatic conditions.

抄録全体を表示

The present study applied an estimation method of watershed-scale storage based on hydrograph separations and storage-discharge formulizations for exploring the relationship between watershed-scale storage and slope failures occurrences in a watershed. Firstly,we separated hourly discharge by the filter-separation autoregressive method into three to four different discharge sub-components. Secondly,we applied a storage-discharge formulization method to the discharge sub-components separately for estimating the watershed-scale"dynamic" storages under the slope failures occurrences. The results showed the estimated watershed-scale "dynamic" storages would be effective indicators of slope failures occurrences.In addition,we found the estimated watershed-scale storages for faster components were comparable with the Soil Water Index that is the current alert index of slope failures occurrences in Japan.

抄録全体を表示

The evaluation of soil moisture content is important in forecasting flood and landslide disasters. The authors previously proposed a method for estimating soil moisture content on the basin scale based on a tank model; however, determining model parameters from the observed values has been a problem to be solved in generalizing the proposed method. In this study, determination of parameters from geological information was attempted. First, the rainfall, snowmelt and evapotranspiration of the Ishikari River basin were estimated. Next, a relational expression between the parameters of the basins of tributaries and the geologic surface area ratio was obtained, and the discharge of the Ishikari River basin was simulated based on the relational expression. As a result of the simulation, the method for determining parameters based on the geologic surface area ratio was thought to be useful in generalizing the evaluation method for basin-scale soil moisture content.

抄録全体を表示

In Japan, about 70% of the land area is mountainous and provides water resources to the remaining 30% of the area, where agricultural, industrial and urban activities are held. Projection of the impact of climate change on water resources at the local level would provide useful information to decision makers formulating policies for climate change adaptation. Therefore, the accurate estimation of low flow in the mountainous basin is very important for the water resources management now and in the future. This study focuses on the storage-discharge equation and its optimal parameters of the low flow. We prepared 7900 sets of the two parameters, the fractional recession constant Au and the storage exponent value N in the storage-discharge equation, to examine the sensitivity of these parameters in the process of the calculation of low flow. We carried out the hydrological analysis using the hourly hydrological model for two basins in Japan: the Sameura Dam basin located in the western Japan which has variability of rainfall, and the Shirakawa Dam basin located in a region of heavy snowfall in the eastern Japan. The result showed that the optimal sets of the Au and the N, which obtain lower relation error in the hydrological analysis, are expressed in the exponent function of the Au and the N.

抄録全体を表示

It is generally thought that runoff phenomenon at the time of a flood is consisted of a number of runoff components, and historically rainfall-runoff model considering multi-layer flow in a slope is proposed. The purpose of this study is to propose the runoff model in consideration of multi-layer flow and to indicate possible application of long-and short-term runoff analysis. This paper shows outline of proposed rainfall-runoff model considering multi-layer flow in a slope. Additionally, it argues over the difference of reproducibility from existing model. Moreover, this model is applied to long-and short-term runoff analysis at the Kusaki dam basin (254km2). In conclusion, the model considering multi-layer flow was able to be proposed by incorporating no difficulty involved vertical infiltration mechanism to the existing model. As a result of runoff analysis at the Kusaki dam basin, the availability of the proposed model is shown.

抄録全体を表示

In this paper, the runoff system composed of hillslope runoff generation model and channel network is used, and theoretical differential equations to calculate the first- and second-order moments of discharge are derived on the assumption that the deviation from average rainfall is described by AR(1) process. The following results are obtained. The variance of discharge in a steady state is regarded as constant when the catchment area is smaller than one hundred and several tens to several hundred 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 under the impact of mutually dependent rainfall inputs.

抄録全体を表示

A method for establishing stage-discharge rating curve (H-Q curve) in a flood event was discussed, which used a runoff model to the rainfall data and the water level data observed in a basin. A quadratic function that represented the H-Q relation in the river channel was built into the runoff model. When the observed water level hydrographs during a flood event was reproduced by the model, the H-Q curve was established. The method was applied to four water level stations in Dokigawa River basin, and the established H-Q curve was compared with the H-Q curve based on the runoff observation. The error margin of the established H-Q curve and the observed was about 5% or less. The proposed method can be used to verify and adjust the observed H-Q curve that may lead to an unsatisfied water budget of rainfall and discharge for the basin.

抄録全体を表示

Tropical Cyclones (TCs) have caused severe disasters in various places in Japan. Kochi prefecture has experienced TC disasters various times, and thus, it is important to evaluate impact of future change of TCs on Kagami river basin. In this study, we developed an algorithm to evaluate the impacts of future change of precipitation caused by TCs into discharge. The algorithm classifies TCs into some patterns according to track and intensity of TCs. Then, stochastically simulated TCs are classified into the extracted TC patterns. Subsequently, the functions to generate TC induced precipitation are also estimated for each of TC patterns. Execution of the proposed algorithm to Kagami river basin indicated annual maximum discharge might increase by nearly 30% when we consider 21 % decreasing of central pressure and future change of thermodynamic environment.

抄録全体を表示

This paper deals with a methodology to estimate the variations of flood hazard and risk due to a climate change. A pseudo global warming (pgw) experiment result of the Isewan Typhoon in 1959 is used as the rainfall input with a climate change effect to a distributed rainfall-runoff/flood inundation (DRR/FI) model. The simulated rainfalls of the control run (ctl) for the reproduction of the Isewan Typhoon as well as pgw experiment by JMA-NHM exhibit that, though the 48-hrs rainfall of ctl underestimates the observation, the maximum hourly rainfall of pgw becomes much higher than the observation. As the result, the simulated water level/discharge and inundation depth with pgw rainfall becomes all worse than those of the Isewan Typhoon.

抄録全体を表示

We present here a novel system that predicts stream flood condition on a real-time. The system drives LSM-coupled distributed hydrological model to simulate river discharges as well as basin's water balance components, such as soil moisture, on hourly basis. In the meantime the system evaluates past Quantitative Precipitation Forecast (QPF) performance with respect to C-band radar derived observed rainfall for generating ensemble QPF members. The system then simulates ensemble stream flow forecast by taking real-time hydrological model output as initial condition and ensemble QPF members as forcing. The system is applied to the Upper Tone river basin, showing promising performance for the recent three typhoon cases. Being integrated with data-archive, this approach can be operationally used and its application to other river basins is widely possible.

抄録全体を表示

This study aims to develop a real time flood simulation model in an urbanized low-lying river basin (Tsurumi river of Japan). The model has been developed by enhancing the distributed hydrological model (WEB-DHM) to account for urban land surface characteristics and effects of flood control ponds and coupling 1D unsteady flow model to the enhanced WEB-DHM. The enhanced WEB-DHM model computes the flow rate in the upper stream and the 1D unsteady flow model computes the time-varying water surface level in the lower stream accounting for tides and effects of retention ponds. The system has been validated against past flood events along the study region with acceptable accuracy.

抄録全体を表示

The model to predict water level from precipitation directly was built by the storage function method and an H-Q equation. Because this model does not use flow quantity in calculation process, this model is available in a flood prediction at the water level station not to get adjustment of flow quantity and the precipitation, and not to observe flow quantity. The constant number of this model is expressed in a selfregression model and Unscented Kalman Filter is applied to data assimilation technique. As a result of having applied this model to the Doki River basin, we obtained an almost proper result by setting selfregression coefficient and a system noise appropriately. In addition, it was revealed that the flow quantity counted backward accorded with flow quantity estimated by the storage function method. Therefore, it was understood that the built model reflected a rain-runoff process.

抄録全体を表示

In this study, an experimental observation using the ground-based microwave radiometer for Oats was carried out in order to understand the microwave characteristic of vegetation effect. First, vegetation parameter, single scattering albedo and vegetation's fractional area were calculated using the observed data, and the reliability of experimental observation's result was checked by the comparison with an observed microwave brightness temperature and a calculated brightness temperature based on the calculated vegetation parameter and single scattering albedo. Furthermore, the estimation method of snow depth in snow cover area over the North Eurasia was investigated based on the calculated vegetation parameter, single scattering albedo and vegetation's fractional area. In the result, the estimation accuracy of snow depth was improved by the introduction of vegetation's fractional area based on the mix-pixel model.

抄録全体を表示

Nowadays, global warming has been a hot issue. Melt water from tropical glaciers in the Andes is used as important water resources and retreat of the glaciers raises risk on the water availability in the future. Therefore water resources management is necessary, and it is important to investigate water balance in the snow-fed and glacier-fed basins in order to understand how much water is coming from snow and glaciers. This study challenges this issue, and the main purpose of the present study is to estimate glacier melt water in Tuni Lake basin, Bolivia which supplies water to the capital area. Because study area is located in high altitude, we could use limited data. From this point the degree-day method may be suitable for estimation of the glacier melt water. However, we need to determine degree day factor in the method. Therefore, we estimated the glacier melt water first by using a water balance method in order to determine degree day factor in the target basin.

抄録全体を表示

This study aims at figuring the roof snow loads to prevent accidents associated with roof snow removal or to reduce the risk of snow-load induced roof collapses. A heat, ice, water and air balance model, i.e. a Roof Snow Load (RSL) model was developed to calculate the roof snow load and the validity of the RSL model was examined by comparing field test results with the computational ones. Consequently, the RSL model successfully reproduced the time changes in the snow height, snow density, volumetric water content and the roof snow load.
Additionally, effects of the heat across the roof (house heat) on the roof snow load were evaluated by numerical simulations using the RSL model. It was found that a coefficient involved in the roof snow load reduction (a snow melt coefficient) decreases exponentially with increasing in the house heat flux.

抄録全体を表示

Moving Particle Semi-implicit (MPS) method is a powerful tool to reproduce flow phenomena with large surface deformations such as avalanches. This study presents some investigations on the constitutive equations for avalanche. Here, we produced a model by applying a combination of Bingham-Dilatant and Hershel-Bulkey constitutive equations. These models were applied to some test cases and evaluated through the comparison with existing experimental data. By using the MPS method, unnatural pressure vibration is resulted. In order to use the MPS method in real structural design, divergence model is employed. This model showed a significant reduction in unnatural pressure vibration.

抄録全体を表示

This paper described Runoff Characteristics in drought period based on Minimum monthlyPrecipitation and Continuous dry days. Therefore, we conducted during September 2005 to August 2007 in the upper Iwaki catchment, Japan with distributed snowmelt runoff model. As the result of the analysis with Continuous dry days, the runoff analysis shows precipitation in July and August have an impact on lack of river discharge, but shows precipitation in June don't have an impact on river discharge because snow contribute to discharge. Moreover, river discharge has decreased about 5m3/s when continuous dry days have 21 days in July. So these shows drought event probability get higher when timing of the appearance of continuous dry days are increasing distance from snowmelt season.

抄録全体を表示

To characterize dissolved nitrogen (DN) export from a forested area, we analyzed relations between DN concentration and stream discharge (C-Q relations) during rainfall-derived and snowmelt-derived runoff in a headwater catchment, the central Chugoku Mountains, based on mixing processes of runoff water components. C-Q relations during each rainfall-derived runoff showed strong correlations, and the slopes of regression lines were strongly correlated with initial discharge of runoff, implying that the C-Q relations depended on the mixing rain water and soil water with groundwater. Although the C-Q relation during snowmelt-derived runoff was uncorrelated, very high DN concentration was observed in early phase of the snowmelt period. Eventually, we proposed the estimation method for DN export loading based on initial concentration, initial discharge and variable discharge during rainfall-derived runoff, and pointed out the importance of frequent sampling in early phase of snowmelt period for the load estimation.

抄録全体を表示

Upper bound for the total amount of precipitation is an important factor in determining the design discharge. The probable maximum precipitation can be examined by solving the governing equations of the hydrological processes, while the spacial distribution should be supported by evidence of the past records in the statistical sense. To estimate the upper bound will be a harder challenge than to do the return levels against finite return periods, because the degree of experience become to zero for the upper bound. This paper points out the difficulty which is caused by a trade-off with increasing sample size, and demonstrates how it appears by the numerical simulations.

抄録全体を表示

Global warming projections by global climate models (GCMs) are very helpful to investigate effects of future climate changes. However, the spatial resolutions of GCMs are not enough for detail assessment of future climate conditions and their effects in a river basin. A dynamic downscaling method by a numerical weather prediction model is applied to present and future climate in the Ara River basin in the Kanto region of Japan. Results for present climate show significant overestimation in annual precipitation around the basin, however, patterns of seasonal variation and spatial distribution are similar to the actual conditions. In future, decreasing annual precipitation is shown in one global warming projection, but insignificant variation in another. On the other hand, amplitude of inter-annual variation becomes larger in both results. Minimum annual precipitation in future are smaller than at present and frequencies of small precipitation year increase in future. These results indicate increasing negative effects on future water resources.

抄録全体を表示

Climate change is predicted to reduce future crop yield through a change in the amount of precipitation and have impact on food security. The risks of health damage attributable to undernourishment under climate change need to be quantified. This study assesses health damage using Disability Adjusted Life Years (DALYs) under the latest climate change scenario. A model for estimating DALYs attributable to childhood underweight (DAtU) is developed using the relationship between DAtU and childhood stunting. The results show that socioeconomic condition has greater impact on future health damage than climate change though there are various uncertainties. Differences in the projected amount of precipitation have an impact on the results especially in South Asia. Other climate conditions and differences in global economic models can also be critical factors for future health damage.

抄録全体を表示

Tropical cyclones (TCs) are often associated with heavy rains and storm surges that bring severe damage to human society. Previous studies have indicated the possible increasing of TC intensity in the future. Thus, it is important to predict future TC losses. In this study, we developed regression models to estimate economic losses caused by TCs at global scale. The models used pressure drop, exposed population and gross domestic product (GDP) per capita as inputs. Furthermore, economic losses in 2100 were projected by considering socioeconomic and/or climate change based on A1B scenario. In addition, future losses with socioeconomic and climate change under four different social scenarios were also estimated. In the results, global economic loss and ratio of economic loss to GDP would increase with socioeconomic and climate change. The increase of losses is mainly because of socioeconomic changes (particularly in the North Indian and the Southern Hemisphere regions) rather than climate change.

抄録全体を表示

Trans-boundary river basins have been affected by flow variability caused by water use. Down-stream countries are often forced to face water shortage and sometimes dispute and compete with up-stream countries for shared water resources. To avoid future water conflict, the basin at risk should be identified by hydrological variability and institutional mechanisms which agreements contains. This paper investigates the potential risk for trans-boundary water conflict in the future. This risk can be estimated with two components. One is water stress level projected by a global water resource model and the other is vulnerability level defined by both trans-boundary freshwater agreement and river basin organization. As a result, the potential risk for trans-boundary water conflict in Africa and Central Asia is found.

抄録全体を表示

Virtual water trade was originally a metric illustrating how food import potentially alleviates water shortage in the importing states and regions by reducing water demand for food production. However, now it is widely used to indicate exogenous water resources. It is known virtual water importing to Japan is relatively higher than other countries, but this has not been directly related to water shortage in developing countries. Nevertheless, quantitative estimate of virtual water import to Japan is gathering a lot of attentions. In this study, the transition of the virtual water import in 2010 was estimated. It was found that the total change is not substantial but the changes for each products were significant. Virtual water in crops increased from 36.82 (km³/year) in 2000 to 42.84 (km³/year) in 2010, and it decreased from 27.60 (km³/year) to 20.21 (km³/year) in meat. It was indicated the share changes of the United States (i.e. 6.67km³ of 7.39km³) mostly contribute to the total changes of virtual water imports in meat.

抄録全体を表示

Precipitation analysis for several heavy rainfalls that occurred in Nagoya City was performed based on 10-minute and hourly precipitation data. Rainfall distribution analyses showed that a rain band in the direction of the prevailing wind at middle levels was formed in 9 out of 10 major heavy rainfall events in past 56 years. The rain band consisted of aligned heavy-rain cells of about 5–10 km diameter that traveled successively along the rain band that was generated on a meso-scale convergence line. Also, the result of rainfall analysis using 10-minute precipitation data was compared to rainfall distribution based on XRAIN (X-band polarimetric RAdar Information Network, that was installed in Nagoya area in 2010) for the rainfall event in 2011 and its validity and precision was evaluated.

抄録全体を表示

In recent years, flood damage in urban areas due to localized heavy rain has increased. In order to reduce the flood damage, improvement of rainfall forecast accuracy has been expected. To improve the rainfall forecast system (radar image extrapolation method), we have developed a technique to identify the stage of storm life cycle. This is the first study to identify the stage of storm cell using a hydrometeor classification which is estimated from X-band polarimetric radar observations.
We investigated the relation between the stage of storm life cycle and existing ratio of hydrometeor aloft in a storm cell. The membership functions between the stage and hydrometeor existing ratio was created based on the tracking results of storm cells. The result of applying fuzzy logic using the membership function to various storm cells shows a good agreement.

抄録全体を表示

In Japan, flooding damage of urban area caused by local heavy rainfall is increasing in recent years. It is of great importance to improve the precision of forecasting local heavy rainfall. However, present weather forecasting system cannot forecast the local heavy rainfall well in advance since local heavy rainfall has small scale and grow suddenly. In this study, therefore, we develop two early local heavy rainfall forecast techniques at Osaka city. One is the weather index technique, and the other is numerical weather forecasting technique by assimilating the X-band multi parameter radar(X-MP Radar). As a result, we can forecast local heavy rainfall earlier by weather index technique, and we can express the movement, strength and detail structure of local heavy rainfall using numerical weather forecasting technique by assimilating X-MP Radar.

抄録全体を表示

The Ministry of Land, Infrastructure, Transport and Tourism (MLIT) built the rainfall observation network composed of 35 X-band dual polarimetric radars called XRAIN. The purpose of this paper is to improve observation accuracy of the radars rainfall of XRAIN. The method of radar rainfall estimation of XRAIN uses Z-R and Kdp-R relationships. The results of sensitive analysis about the thresholds of condition to use Kdp-R relationship expanded the use condition of Kdp-R relationship. The expansion of the use conditions of Kdp-R relationship, the frequency of use of Kdp-R relationship is increased, observation accuracy of radar rainfall is improved.

抄録全体を表示

In recent years, the local heavy storms rise frequently and have caused flood disasters in urban areas in Japan. Due to unexpected and disorderly behavior of the local storms, their actual conditions are unknown from observation by rain-gauge networks on the ground. This research aims to verify the rainfall information by the X-band Multi-Parameter radar, and to clarify the temporal and spatial characteristics of the local storms based on the radar information for consideration of influence on the flood runoff of urban streams. After the accuracy verification of the radar rainfall data by comparing the radar and the ground rain-gauges, efficiency of the average rainfall over watershed based on the rain-gauges are inspected by the radar data in the watershed. From the viewpoint of the random field, the stochastic properties of the heavy storm distributions are evaluated with the variogram of radar data.

抄録全体を表示

This paper analyzes errors of X-band MP radar rainfall and proposes a method to stochastically generate rainfall fields reflecting the error structures. By introducing multivariate AR model with Cholesky decomposition, the presented method reflects both space and time correlations, the latter of which could not be represented in a previous method. The proposed method is applied to Typhoon events in the Chikusa River Basin to generate conditioned random rainfall fields to analyze the uncertainty in rainfall-runoff predictions. The analysis indicated that the average relative errors in X-band MP radar rainfall are about 0.3 to 0.4 within 40 km range from radar sites. The errors propagate into the uncertainty in peak discharge estimates with about 0.1 of coefficient of variation. Further analysis with assumed different errors in random rainfall fields and their impact on streamflow predictions is also presented.

抄録全体を表示

To measure the falling velocities, the diameters and the aspect ratios of raindrops, consecutive images of raindrops in the open air outside of our laboratory were captured by an ultra-high-speed video camera. For automatic image capturing and avoiding the damage to the image sensor of the video camera due to the strong continuous illumination, a new trigger device was newly introduced to the capturing setup.
As a result of the image analysis of the falling raindrops images, the following findings were obtained, when the equivalent raindrop diameter is smaller than 3mm. (1)The relationship between the falling velocity and the raindrop diameter determined by our outdoor measurement is similar to that between the terminal velocity and the water drop diameter determined by Gunn and Kinzer's indoor experiment. (2)The aspect ratios of raindrops determined by our measurement is similar to that calculated by Pruppacherr's model of raindrop.

抄録全体を表示

This paper discussed estimation method of probable maximum value of extreme precipitation. We analyzed the 99th percentile of 10-minutes and 1-hour precipitation for each daily average temperature bin based on observational data in Sapporo. Even if temperature is lower than zero degrees, 99th percentile precipitation intensities tend to have an approximation equation that rate of the precipitation increase was almost same as the Clausius-Clapeyron like relation. We estimated the future 99th percentile rainfall intensity under climate change condition by using the projected future temperature in a dynamically downscaled temperature in the Regional Spectral Model (RSM).

抄録全体を表示

We developed a satellite-based land and cloud data assimilation system coupled with the Weather Research and Forecasting Model (CALDAS-WRF) and applied to the Kanto area. The CALDAS-WRF includes Simple Biosphere model version 2 (SiB2) as a land surface driver, radiative transfer models for surface soil layer and atmosphere as observation operators, and Ensemble Kalman Filter (EnKF) and 1DVAR as assimilation algorithms for land and cloud, respectively. The CALDAS-WRF first assimilates the soil moisture heterogeneity, using passive microwave brightness temperature (Tb) at lower frequency, which has a high sensitivity to soil moisture. Then the CALDAS-WRF assimilates cloud over the land, using Tb at higher frequency, which is sensitive to cloud, and optimized emissivity of land as a background information. The experimental results in the Kanto area show that the CALDAS-WRF effectively assimilated information of clouds, improved the representation of cloud distribution, and also affected atmospheric field around the cloud area about one hour after assimilation.

抄録全体を表示

Numerical sensitivity experiments are made to investigate better combination of physical schemes in a meteorological numerical model, i.e., The Weather Research and Forecasting (WRF) by comparing numerical results with radar-AMeDAS data. The numerical experiments are carried out in three nested computational domains to simulate the heavy rainfall event in northern Kyushu in July 2012. It is difficult to predict accurately precipitation at a local point even through the latest meteorological model. The present study also examines whether computational precipitation averaged within spatial scale can provide practical precipitation or not. The time lag of hourly precipitation and the relative error of total precipitation simulated by the WRF model vary depending on the scheme combination and the spatial scale for averaging. The WRF model with the better scheme combination reproduces approximately spatial distributions of 12-hours accumulated precipitation from the radar-AMeDAS data. The present results suggest at there is an effective spatial averaging scale for evaluating practical precipitation.

抄録全体を表示

We focus on the Probable Maximum Precipitation (PMP) in the Upper Tone River basin, through weather conditions change. In order to evaluate total amount and distributions of heavy rainfalls, WRF model is used. The results are summarized as follows: (1) The increase of relative humidity in the atmosphere affects not only total rainfall but also its temporal variation and it also makes peak time earlier. Moreover it may generate a first peak before main peak rainfall, which will affect the initial loss of rainfall and increase maximum discharge. (2) The increase of wind speed affects not only total rainfall but also spatial distribution of rainfall. (3) Moisture fluxes show high correlation with total rainfall through grid point value (GPV) data from meso-scale objective analysis and WRF model calculation in the upper Tone River Basin, which clearly suggests they can be used as a suitable parameter to estimate PMP.

抄録全体を表示

The current study conducted numerical experiments using nonhydrostatic mesoscale meteorological model to evaluate and verify the mitigating effect of weather modification by cloud seeding on torrential rains. Based on simulated two heavy rain events in the Kitakyushu and Tokai regions of Japan, sensitivity analysis was performed by manipulating some conditions of cloud seeding implementation, i.e., area, height, time, etc., in incremental steps. Some standpoints of evaluation were introduced in the analysis to clarify whether and how far cloud seeding have a significant influence on precipitation systems. Results show that rainfall area and hourly rainfall, as well as maximum areal rainfall, can be decreased by cloud seeding, depending on the condition of its implementation, and that the number of cases with rainfall mitigation tends to be greater than that with rainfall promotion. It was also clarified that rainfall mitigation by cloud seeding can be attributed to the leeward migration and/or diffusion of precipitation particles with excessive increase of ice crystals in upper layers of the atmosphere.

抄録全体を表示

Recently, heavy hourly precipitation has been observed in Japan. It seems that intensification of heavy precipitation is related to urbanization, heat island phenomenon and global warming. But to clarify the change of hyetograph patterns, it is necessary to take a statistical test about time series of temporal and spatial distribution. In this paper, trend analysis of temporal distribution of hourly precipitation is carried out by Mann-Kendall test. The temporal concentration degree of precipitation is quantified by a gradient of ID (Intensity-Duration) curve. By applying to the hourly precipitation dataset form 1890 to 2012 at Tokyo and 1891 to 2012 at Osaka, it was showed that the temporal concentration degree is increased in August at Tokyo. Furthermore, it was proved that the long term data is useful for trend analysis of temporal distribution of precipitation.

抄録全体を表示

Severe floods in Pakistan brought many casualties and economic losses in 2010. It is reported that global warming has potential to increase a risk of extreme climate event. Recently a new approach called Event Attribution was developed to quantify the contributions of global warming to specific climate events such as floods in Pakistan. In this approach, large ensemble simulations are generated by an atmospheric general circulation model (AGCM) both under realistic climatic conditions and ideal climatic conditions assuming global warming is not occurring. Those simulations indicated that a specific pressure pattern associated with a wave train from Russia, which is natural variability rather than global warming, enhanced rainfall in Indus River Basin in 2010. Taking advantage of the large ensemble, we investigated how the rainfall developed to the extreme heavy rainfall in 2010. Composite analysis showed that unusual moisture convergence from Arabian Sea due to the specific pressure pattern had played an important role to cause heavy rainfall in 2010.

抄録全体を表示

It is essential to assess the crop growth state because the agricultural water usage is dominant to total water consumption whole the world. One crop model which is written by empirical formula and another crop model which is described by the basis on physiology are successfully coupled with the land surface scheme, SiBUC to assess the climate change impact on irrigation water requirement by MRI-AGCM3.2S. Simulated irrigation water requirement is larger than the statistic water withdrawal so the change tendency of irrigation water requirement by climate change is analyzed. It is assumed that the empirical crop model could be representative of crop which has shorter growth period and the physiological one could describe longer term crop growth.

抄録全体を表示

To improve the skill of reproducing land-atmosphere interactions in the weather forecasting system, simultaneous modeling of surface soil moisture (SSM) and leaf area index (LAI) is strongly needed. We develop a hydrological-dynamic vegetation coupling model and its optimization scheme assimilating microwave signal. The model parameters including land surface, vegetation and radiative transfer processes are estimated by using microwave satellite data and the optimization scheme. From the model application at an in-situ observation site in West Africa, we clarify that our system has a good performance to calibrate both hydrological and dynamic vegetation model without ground observed data.

抄録全体を表示

Thailand has the extreme dry season and rainy season because of the tropical monsoon climate. They have suffered from droughts and floods almost every year and both have caused much damage on agriculture. The objective of this study is to estimate the effect of precipitation fluctuation on production of rice and maize in north Thailand. The statistical analysis using agricultural data shows what factor is determinant for production fluctuation of each crop. The correlation analysis between SPI, which is a simple indicator of precipitation fluctuation, and fluctuation of crop production indicates that there are some provinces where yield fluctuation of crop grown in rain-season shows positive correlation with SPI and harvested area fluctuation shows negative correlation with SPI. It also shows that in some provinces, planted area of rice grown in dry season depends on precipitation fluctuation.

抄録全体を表示

Soil moisture plays a key role in climate systems through its strong impacts on water and energy cycle between land surface and atmosphere and contributes to improvement of weather and water resources predictions at regional and global scales. In addition, soil moisture distribution at very local scale, such as a farmland one, is useful for agricultural activity and management. Therefore, Synthetic Aperture Radar (SAR) is expected to observe soil moisture with high spatial and temporal resolutions. The purpose of this study is to consider the frequently-applicable algorithm for soil moisture by coupling the multi-polarimetric and the single observations obtained by the Phased Array type L-band Synthetic Aperture Radar (PALSAR) onboard the Advanced Land Observing Satellite (ALOS).

抄録全体を表示

Droughts cause severe human and economic damage and appropriate drought monitoring is important to reduce damage. Drought indices are one of the effective methods for drought monitoring. Drought indices which can evaluate drought spatially are required for detailed drought monitoring. The objective of this study was to develop a drought index, SDT (Standardized Difference Temperature), and show the usefulness of SDT. SDT focuses on the diurnal range of land surface temperature, using satellite images for spatial evaluation. SPI (Standardized Precipitation Index) was used to evaluate the usefulness of SDT. The results showed that SDT and SPI have good correlation in the beginning of the dry season and that SDT is valid for drought monitoring in these periods.

抄録全体を表示