A 3D numerical model has been developed for investigating the complicated relations between cloud, convection, radiation and surface energy budget. Using this model, a sensitivity analysis of radiation to surface energy budget and two kind of numerical experiments have been performed and following results are obtained: 1) Net radiation at the ground surface has a maximum value at a lower water cloud content. 2) Radiative cooling of atmosphere restrains the development of convective layer. 3) Radiative cooling of cloud activates the development of cloud top.

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The present study deals with the bulk parameterization scheme of cloud microphysics which predicts the mixing ratio of six water species, i. e. water vapor, cloud water, cloud ice, rain, snow and graupel. This scheme is applied to the 2-dimensional simulation of the convective snow band which occured over the Japan Sea off the coast of Niigata. The simulation showed that convective snow band occured over the sea, and decayed its scale as soon as enter over the plane. Sensitivity experiments on the changing of collection efficiency of riming process showed various patterns of the formation of the snow precipitation. And conversion term from cloud ice to snow also plays a very important role in the formation of snow precipitation.

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A new analytical method of wind field considering stratified atmosphere is presented. The analytical solutions of wind u, v, and w were obtained by using the perturbation method and double Fourier Transform for the basic equations. The solutions can be applied for arbitrary topography of basins in meso-βA scale. The results of analysis show following characteristics. 1) Ascending wind is suppressed by stratification effects of atmosphere comparing with potential flow. 2) In the case of the range of mountain, it is shown that blocking appears in the case of less than the critical internal Froude number. 3) In the case of internal Froude number sufficiently larger than the critical number, the solution approarchs asymptotically the one for potential flow.

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To estimate air moisture flux (Ms), 400 points meteorological data at the surface of the Japan Sea are analysed on the assumption of adiabatic change. The wind field at the upper-layer (900, 850, 800hPa) was obtained from thermal wind.
Estimated Ms is nearly close to air moisture income (Ma) culculated by aerological data. The air moisture balance δM is high correspondance to the monthly precipitation amount. Spatial distribution of Ms over the Japan Sea is clarified and Ms is significantly affected by the sea surface temperature.

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As the first step for analysing the long term interaction between precipitation and soil moisture by coupling an atmospheric model and a runoff model in which soil moisture and evaporation are formulated, this study investigates effect of the water vapour flux from the ground surface into the distribution of precipitation. In this study, one-dimensional cumulus cloud model by Fritsch and Chappell and a warm rain model by Kessler are introduced into a mesoscale model developed by the authors, and the water vapour is assumed to be supplied from a certain area of the ground surface, specifying the amount of turbulent transfer at the lowest grid points.

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The raindrop size distribution (DSD) was observed with electro mechanical disdrometers. Instantaneous rainfall intensity of each 1 minute was estimated for 82 days measurement. The observational period contains severe rainfall by both typhoon and front with low depression. The dependence of the probability distribution of rainfall intensity and the fractional time of rainfall on accumulation time was presented. These results are considered to be helpful to understand the relationship between the spatial variability and spatial scale. The auto-correlation and power spectra was calculated using 1 minute sequential rainfall data. Result shows the characteristic time scale of 4-5 minutes, 10-15 minutes, 40 minutes and 300 minutes.

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The forecasting approaches based on Remote-Sensing techniques have been developed. But there are difficulties in these approaches because of computational performance which is calculated in time and capacity of computer. This work is the method of forecasting the variation of clouds with Neural Network. Neural Network is defined as that application of the model of brain and neuron systems to engineering and is useful to analyze the infrared and visible images of GMS. Many characteristics of GMS images such as ground data, temperature and wind are stored in a Neural Network for forecasting rainfall. The range of imagery data was reveled through the comparison between infrared and visible imagery data to estimate rainfall.

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It is important to estimate dam design flow for dam construction. In Japan, design flow must be selected from different three approaches, probable flood in 200 years, observed maximum flow and maximum flow estimated for the subject area. But these approaches are mainly based on the observed data. In case of an extremely heavy rain, the inflow may be beyond the maximum observed value. So in this paper, based on observed precipitation data, probable maximum precipitation are calculated from maximum precipitation with specific humidity. and compared with probable precipitation in 200 years

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It was found that the daily and 10-daily rainfall at a station corresponding to a given level of cold cloud cover fraction Fc=0.3 depend on the annual rainfall at the station. This dependence will be called as “Annual rainfall effect”. The effect indicates that the rainfall phenomena strongly reflects the local geographical, meteorological and other conditions that determine the amount of annual rainfall. The precision of regional as well as global estimates of precipitation would be improved by including the average annual rainfall in the estimation formulae.

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The effect of vegetation on the physical and chemical characteristics of rainwater that is delivered to the soil is investigated through observations of 13 rainfall events for a watershed with deciduous and coniferous vegetation. Lumped characteristics of the resulting throughfall (ThF) and stemflow (SF) are analyzed in comparison to rainfall characteristics. Certain factors, such as the kinds and size of trees for stemflow and the distance from the stem for throughfall, were also investigated to determine their relationship to the quantity and quality of SF and ThF. To check the observed data, a tank model is used to model SF and ThF rate and concentration. Results shows that 71% of the rainfall becomes ThF and that the SF rate is 22 times that of the rainfall rate. It was also found that SF is highly dependent on the tree both for the rate and the quality. Due to the characteristics of the basin, ThF is found to be independent of tree characteristics. Finally the tank model is found to be sufficiently capable of modeling SF and ThF rate and quality.

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The flood prediction is difficult because runoff process is distinctly non-linear especially with short time interval hydorological data. Based on the runoff analysis of the 15-minute hydrological data by the filter separation AR method, this paper explains the hydrological runoff process and shows the relationship between pre-flood discharge rate and groundwater infiltration capacity, as well as the relationship between area ratio contributed to runoff and catchment area storage volume.

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This paper studies the flood analysis by the use of direct correlations between precipitation data measured byde nsely distributed rain gauges and flood water level, and shows the applicability of the proposed method for the small river in an urbanized area. Runoff characteristics in an urbanized river is also discussed on the basis of the estimated discharge.

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The channel flow is considered as the rainfall which passes through the infiltration area, where the distribution of pores is assumed as fractal. Using these assumption and the estimation of the characteristics of slope distribution, the method of the lumping of a hillside and the value of fractal number δ of the pores of the infiltration area in a hillside (δ=1.8) are obtained. It is also found that in mountainous basins where the areas are less than 0.2km² the delay of runoff is nearly 20 minutes and that the Manning's coefficient n is nearly 0.05 (m^-1/3·s).

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Scale effects of basin elements on coefficients in runoff-erosion modeling are discussed by dividing a small test field with the area of 5200 m² in Brazil into elements in three ways: 4, 10 and 23 elements. Standardized Powell method is applied for the optimization of parameters in the model. Simulation results of runoff, sediment yield and the coefficients for the three ways of basin division proved that in this particular case the precise division of the river basin into small elements did not always give better result. Although the 10 elements division gave the best results, even simulation results by only 4 elements division were fairly good.

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The authors have, conducted laboratory experiments to investigate both the role of atmospheric factors in the melting process of snow and the effect of infiltration into the sand layer. Laboratory experiments are performed using two layers which are chipped ice layer or snow layer and sand one.
From the results of these experiments, in a limited range of wind speed, it becomes obvious that the volume of snowmelt water is good related with wind speed and the effect of wind speed is important for the melting process of snow.

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Parameters used in models to forecast a snow depth from precipitation, to describe the deformation process of the snowpack and to calculate the snow-melt run-off are investigated in Waga river basin.
A rain or a snow is distinguished by using the air temperature as an index. The density of freshly fallen snow are measured in the field. Long term deformation of a snow pack is expressed by Burger's model and viscous coefficient of a snow is obtained from laboratory experiments as well as from the change in the depth of snow layers.
Degree-hour factor and the amount of snow-melt ground heat are also observed in the field.

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A hydrogeochemical study was carried out to investigate the chemical composition of new snow and ellution of ions through snowpack in the winter 1993. The area and the test-sites, where snow pit observation and snow cores sampling were done, are in the Mt. Hakusan at the altitude of 460m to 860m. We collected snow cores evry week during the winter, and analyzed them for pH, NO₃^-, SO₄^2-, Cl^-, Na⁺, Mg²⁺, Ca²⁺ and K⁺.
SO₄^2- and NO₃^- mainly contributed to acidification of new snow with the mean pH value 4.6. The pollutants were released from the pack due to episodic melting and wet metamorphism of snow during snow season, and the most part of pollutants flowed away from snowpack before melt season.

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Snow volume in Tohoku district is evaluated by NOAA satellite remote sensing and snow distribution model. It is assumed that snow depth is proportional to the elevation from the snow line. This propotional coefficient is evaluated from AMeDAS data in Tohoku district. An algorism to obtain the snow line is also developped. As the result, this coefficient is obtained 0.26 the same as the observing values. This result applied in Tohoku district and snow volume is estimated 24.8 km³.

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Annual water balance is investigated in the Taki dam basin, which area is about 2, 000km² and has heavy snow area. A method of snowfall correction on precipitation, the Thornthwaite method on evapotranspiration and a simple balance model on ground water are applied to evaluate each components in hydrological cycle and the total balance is discussed. Snowmelt volume is calculated from both the tank model and water balance equation and the runoff delay of meltwater is discussed. Conclusions are; 1. snowdepth distribution depends on the total snowfall volume 2. actual evapotranspiration can be estimated by the Thornthwaite method and 3. daily snowmelt runoff is almost constant.

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This paper describes the mechanism of evaporation in a sand column under a diurnal temperature variation. Thermo-hygro meters were used to obtain the vertical profile of water vapor density along a sand column. The correlation between air temperature and evaporation rate is positive and the evaporation rate is high when the air temperature is high. There is, however, a time delay between these two time series and it mainly depends on the time change of the water vapor density at the top of capillary zone. As the dry layer becomes thick or the level of groundwater table becomes low, the time delay gets larger. It is concluded that the diurnal evaporation variation can be well explained by the diffusion theory of water vapor.

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A dynamic mathematical model is proposed to simulate the moisture and energy fluxes in a plant ecosystem. Hourly and daily processes of five important variables---leaf temperature, leaf moisture potential, air temperature and humidity within the canopy, and temperature on soil surface---can be gained by using the model. Temperature difference between plant leaves and surrounding air is paid attention, and difficultly-measured plant potential or temperature could be derived from normal meteorological data.

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This study investigates an estimation method of basin transpiration based on heat pulse velocity and micrometeorological data by making use of solar radiation on several slopes which consist a basin. The basin transpiration is calculated by the weighted mean of transpiration on each slope, taking advantage of the area of each slope. The proposed method is applied to the data observed in the Shirakawadani experimental basin in Tokushima prefecture. The cumulative transpiration over several months agrees with the estimation by water budget method.

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In this paper, a three dimensional numerical evapotranspiration model was applied to the basin of Lake Biwa.
To compare the results by simulation with other studies, the numerical model was considered to be valid. Moreover, the basic knowledge to estimate evapotranspiration from a large field was obtained, such that, for water surface, daily evapotranspiration was closely related to the wind speed averaged over the day. As for land surface, except for forest, daily evapotranspiration was also related to the average wind speed influenced by the radiation.

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This paper presents on a new method for estimating of daily evapotranspiration from mountainous river basin.
First, the actual daily evapotranspiration is estimated by using the observed daily evaporation at a mountainous site. Then, the Hamon's formula under the daily rainfall conditions is presented, and the parameters of the formula are calibrated by the estimated daily evapotranspiration. Finally, the expression is applied to two mountainous river basins, and a validity of the method for estimating the actual daily evapotranspiration and a practical utilization of the improved expression are discussed.

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Land cover classification in Tokoro river basin was done immediately after cutting out the catchment image from the Landsat TM full-and sub-scene so as to superimpose this image on an elevation mesh image. The monthly mean Evapotranspiration (ET) of Tokoro river basin was obtained by Kojima's equation in winter and by Morton's equation in other seasons. The annual change in estimated monthly mean ET, which reaches its maximum value in July, increases as the albedo decrease. The influence of land cover category, land development and air temperature on ET was examined.

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The purpose of this paper is to develop a model for estimating the distribution of evapotranspiration over a wide area covered by forest Vegetation index closely relates to evapotranspiration. Therefore the distribution of NDVI (Normalized Differences Vegetation Index) calculated from NOAA-AVHRR data is compared with the total evapotranspiration evaluated by the conventional method (Thornthwaite method). Correlation between evapotranspiration and NDVI is derived from multiple regression analysis in three basins. It is confirmed that evapotranspiration in a forest is propotional to NDVI. The distribution of evapotranspiration in the basin can be estimated from the correlation.

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NOAA-AVHRR data is used to obtain spatial distribution of evapotranspiration for 5 basins, about 69% of total area of Korea. Amounts of evapotranspiration of these basins are estimated by the Penman method, and NDVI (Normalized Difference Vegetation Index) calculated from NOAA-AVHRR data is utilized to estimate its spatial distribution. Because the NDVI value indicates the activity of vegetations and the NDVI histogram reflects the variation of evapotranspiration, its spatial distribution can be estimated using NDVI. This method will make possible to estimate that of North Korea where meteorological data are unavailable. Keywords: NOAA-AVHRR, NDVI, evapotranspiration, spatial distribution

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The main objective of this study is to develop an methodology for estimating the evaporation from macro-scale hydrologic grid. Macro-scale evaporation formulas, into which the subgrid-scale distribution of related physical equations can be incorporated, were derived from ordinary estimation of formulas of evaporation by means of perturbation method. These formulas are expressed in terms of variance and covariance of the physical quantities. The sensitivity of the sub-grid-scale distributions of surface soil moisture and temperature on the evaporation estimation was examined using bulk method. The major conclusions obtained here are as follows:(1) The estimated values of evaporation is smaller than those without considering subgrid-scale distributions of physical quantities, and (2) Mean and variance of subgrid-scale distribution have the most significant effect on macro-scale evaporation estimation

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It is important to know characteristics of spatial distribution of surface soil moisture in conditions of various kinds of land use. This paper reports some results of the preliminary field survey for investigating the characteristics in bare fields. First, a method of surface soil sampling itself is examined. Second, some characteristics of soil moisture conditons in a dry field and wet paddy fields are studied. Last, spatial scale of distibution of soil moisture content in the relatively wide field is discussed.

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Water path through unsaturated media was examined by computer simulation using ‘water path invasion model’.
Simulation showed the effects of angle of contact and water content. Flow rate produced a significant influence on fractal dimension and width of water path for covering infiltration but no influence for concentrated infiltration.
Simulation with a rectangular network made more realistic water path than that with a hexagon network.

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This research observes the effect of vegetation on the spatial rate of infiltration and on the resulting path of flow inside the soil. Aside from infiltration experiments, paint tests and soil potential measurements were made. Results show that (a) the infiltration rates are dependent on the distance from the tree stem, (b) variations in infiltration rates are small for heavily forested areas compared to sparsely vegetated areas. It was also found that (c) the flow in the soil is mainly vertical. Finally it was found that (d) there is bottom-upsaturation in the soil even for small rains.

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Two-dimensional numerical simulations are carried out to simulate unsaturated and saturated flow in a hillslope and the discharge process from hillslope into river. The soil moisture movement characteristics within hillslope is analyzed in terms of flow pattern and flux distribution. Effects of initial conditions on discharge process are investigated. Based on the numerical simulation results, a simplified hillslope process model is proposed and checked with detailed numerical simulation, which can be used to simulate the water flow within hillslope and interaction with river.

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The movement of groundwater and the water budget in a reclaimed, man-made island was studied experimentally and theoretically. A set of experiments were carried out using a Hele-Shaw model that incorporated a rainfall simulator and a tidal generator. The analysis of free surface and the salt/fresh water interface was done through the Boundary Integral Equation Method (BIEM). The results showed that the volume of fresh water in the island increases when the rainfall intensity increases, and the propagation velocity and volume decrease along the free surface and at the salt/fresh water interface depending on the characteristics of tidal oscillation as well as rainfall intensity. An application of the BIEM to groundwater analysis in the reclaimed island was proved.

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The process of channel inception is studied theoretically. Instead of the normal flow assumption used by Smith and Britherton, St. Venant shallow water equations are adopted as a flow model to include the effect of backwater and the Reynolds stress. Velocity and depth profiles of a sheet flow on a perturbed plateau is analytically solved using a perturbation technique. It is found that the flow is gathered in troughs on the plateau and that the flow intensification is maximized when perturbation wavelength is of the order of the flow depth devided by the slope.

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A new formula of local 2-D dispersion coefficients proposed by Komatsu et al. is incorporated into an ecological simulation model of COD (Chemical Oxygen Demand) and T-P (Total Phosphorus) in Hakata Bay. The 2-D dispersion coefficient is expressed as the product of the local tidal maximum velocity and the local depth. The proportional constant of the formula for COD is found to be slightly different from that for salinity. The model calculations of COD and T-P are reasonably consistent with observations.

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As a method of water quality purification in a bay, it is proposed to use an intake or outlet of cooling water of a power plant. It is shown that the relation of water exchange and water quality, and the calculation results of the change in water quality in the case of taking water from the inside of the bay and draining it into the outside of the bay, and that of taking from the outside and draining it into the inside.

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A near-wall turbulence model is applied to the benthic boundary layer to analyze the diffusive transfer of dissolved substance across the sedimentwater interface. A modified turbulent kinetic energy balance is used to define eddy viscosity and eddy diffusivity in the viscous sublayer. The limiting behavior of turbulence quantities very near the bed is expressed as a power of z, the distance from the sediment-water interface. The predicted flux rate over a wide range of the Schmidt number and dissolved oxygen concentration profile near the bed are in good agreement with observations using microelectrodes.

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In recent years development of high performance of heat pumps enables us to efficiently use the unused potential thermal energy naturally stored in water areas such as rivers, coastal waters, lakes, reservoirs, etc. The present study deals with thermal energy intake from a thermally stratified water bodies. Considering energy conservation in waters and intake systems, preliminary computation of possible amount of thermal energy intake, average coefficient of performance (COP) of heat intake facilities and so on are carried out.

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Heat flux of permeable pavement are estimated and compared with that of bair soil or asphalt pavement in summer.moreover, it was appeared that charastaristics of heat and moisture of permeable pavement was similar to that of soil and sand, respectevely.
As the result, permeable pavement was proved to be effective to relief for heating the atmosphere.

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This paper deals with the salt accumulatiom in a sand column due to the evaporation from a soil surface. A solute balance approach was used to estimate the condensation process of salt component, contained in groundwater. Temperature, volumetric water content, solute concentration proflies and evaporation rate were measured, and the temperature gradient was induced by the radiation. It was found that as the radiation gets stronger, the condensation near the soil surface becomes clear and soon. The computation could provide the time changes of temperature, moisture content, solute concentration profiles and evaporation rate, and could model the salt accumulation.

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When a spring water having reducing property with an about 10 ppm (Fe) of dissolved iron flowed down stream, the iron deposition behaviour along the stream was investigated. The dissolved iron concentration decreased along the stream, finally reaching its lowest limit level (1-2ppm). The resultant hydrous iron (III) oxide was X-ray amorphous. Judging from the variation of the redox potential along the stream, the water kept its reducing property during the early stage of the iron deposition and then gradually changed, finally reaching an oxidizing stage.

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The purpose of this study is to investigate on the moving characteristics of pollutant matters into the soil and water of a golf course. As for the behavior of agricultural chemicals and chemical manures scattered on a golf course under the natural conditions, the on-site experiments were carried out. The test samples of water and soil collected from the sampling points were analyzed by chemical methods, and the concentrations of pollutant matters were clarified quantitatively.

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A numerical model is developed and the results are compared with the measured. The water flow is calculated with the kinematic wave theory applied to a channel network which is constructed by using digital ground height data. Two parameters of the cohesive sediment production q_s=aτ^b are determined, according to land use.

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Urbanization of basins leads not only to pollution by sewage but also to change of the characteristics of hydrological cycle and water quality of natural cyclic flow-components such as ground water flow and surface flow in the basins. Many studies were used to attend to the load of pollutant by sewage. But rare study attends to the load of ground water flow and surface flow.
The purpose of this paper is to describe the character of an urbanized river basin in hilly land, so then in this paper authors estimate the amount of discharge of dissolved chemical compounds, and explain the characteristics of hydrological cycle in the watershed.

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This study focused on investigating the formation process of streamwater quality in small mountainous forested basin. Streamwater and soil water quality were observed and all solutes were classified into three types. In order to comprehend the formation process of the streamwater concentration, typical two solutes, NO₃^--N and SiO₂ were picked up and the relationships among the structure of runoff components and both streamwater and soilwater concentrations were investigated. The roles of runoff components in the formation process of streamwater concentrations were qualitatively discussed.

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In Koyama lake, phytoplankton blooms appear in summer season. This phenomenon might be influenced by the water quality. Therefore in this paper, in order to investigate the mechanism of phytoplankton bloom, the water qualities.in Koyama lake such as pH, Do, turbidity, nitrogen and phosphorous were observed from 1991 to 1993. And characteristics of these water qualities were also discussed.

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In this paper, a field observation on how the characteristics of water quality after the flood in Lake Jyusan change as time progresses and locations in the lake are different is investigated. The period of the field observation is from July to August in 1993.
The processes of the change of water quality with the degree of influence of the flood are studied. Also the relationships between the change of sea level and the characteristics of water quality or flow velocity at the lake mouth near the sea are discussed.

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This paper describes thermal stratification and distribution of water quality conditions in lake Onogawa. The water quality of 8 items was tested, Water Depth, Water Temperature, Turbidity, Electric Conductivity, potential of Hydrogen, Dissolved Oxygen, Oxidation-Reduction Potential and 665nm absorption. Measurment through all the area of the Lake were taken three times in thermal stratification season.
As the results of these observations, the spatial quality conditions are suggested.

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This paper describes thermal stratification and water quality conditions in Lake Hibara. The period of the field measurements is from May to December in 1992. This study particularly investigates the relation between the characteristics of thermal structure and turbidity, dissolved oxygen, and electric conductivity, respectively. The main remarkable conclusions are stown in the following.
This lake indicates that the inflow and outflow gave the influence on water quality and water conditions. The measurement over the lake shows that electric conductivity of southern area in the lake had a tendency to have higher value than that in any other area.

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This paper describes the relationship of the characteristics of water temperature and the conditions of water qualities in Lake Onogawa. The field observation was conducted from Augast, 1991 to October, 1992. As the results of these observations, the relationship of turbidity (TB) to 665nm absorption and potential of hydrogen (pH) to oxidation reduction potential (ORP) are discussed.

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