The phenomenon of coupled heat and water transfer in soil plays an important role as a part of the hydrologic cycle. In this paper, the characteristics of heat and water transfer in the unsaturated soil zone under field conditions were investigated by applying the coupled heat and water transfer model to the soil temperatures and pressure heads which were measured under natural weather conditions. Furthermore, the influences of a correction coefficientζand surface boundary conditions on the changes of temperature and pressure head in the soil, and the estimation of evaporation by a water balance method were discussed. The typical results were as follows: (1)The directions of fluxes driven by soil temperature gradients had complicated daily variations by the changes of the soil temperature profile, compared with those of fluxes driven by pressure head gradients. (2)The flux with water movement was a downward flow in all layers at night (2:00) and in the morning (8:00), but it was a upward flow in upper layers above 10cm in depth in the daytime (13:00, 16:00). (3)The main components of water and heat fluxes were the ql driven by the liquid water movement and the qhc by heat conduction, respectively. (4)The sensitivity analysis of the ζ showed that there were slight differences between the calculated values for each ζ. (5)The sensitivity analysis of the surface boundary conditions showed that the sensitivities of soil temperature and pressure head were greater near the soil surface. It was inferred from this result that the differences between the measured and the calculated values in pressure heads in layers deeper than 25cm weren't affected by surface boundary conditions. (6)Evaporation estimated by a water balance method was used. The amount of evaporation estimated by calculated pressure heads was a little larger than the one by the measured values.

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The factors determining water-use efficiency, net assimilation rate and transpiration rate were investigated using two parameters α(ratio of total conductance to CO2 to total conductance to H2O) and β(ratio of total conductance to latent heat to total conductance to sensible heat, or surface moisture availability). The characteristics of water-use efficiency were detected from several data sets of field observations with porometric method as follows, (1) Water-use efficiency was higher in the morning than in the afternoon. (2) Water-use efficiency was higher in winter than in summer. (3) Water-use efficiency values were scattered mainly from 10-1 to 102 (mg/g), and the fluctuation of water-use efficiency with species was smaller than that with environmental conditions. These characteristics of water-use efficiency reflect the difference of the diurnal and seasonal variation patterns of transpiration rate and net assimilation rate. The phenomena (1) and (2) were mainly caused by the differences in vapor pressure deficit, and partly by the differnces in α, and the phenomenon (3) was caused by the little differences in α with species. Furthermore, the ranges of values of water-use efficiency, net assimilation rate and transpiration rate were discussed using two parameters, α and β.

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Lake Abashiri, located in the northeast of Hokkaido, has stratified layers of fresh and salt water. The biochemical pollution is caused by inflowing load from the catchment area, and no oxygen state of the lower salt layer is becoming a serious problem. In this paper, a numerical model is proposed to investigate the hydraulics of the lake, river and sea region. A general non-orthogonal coordinate system is used to cover the complex boundary condition of the region, and three-dimensional time dependent momentum and continuity equations are used in the model. The model is verified using the two characteristic dataset obtained by field observation. Results obtained by the model agree well with those of the observeton. It is apparent that the model can be a powerful tool for predicting the lake hydraulics.

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The purpose of this study is to develop a macro-scale snowmelt model which can incorporate the sub-grid scale heterogeneity of snow covered area. A spatially averaging technique is employed for scaling up a distributed snowmelt model to a macro-scale snowmelt model which can calculate spatially averaged snowmelt at the grid-scale by using the averaged input data only. We also developed a method of the parameterization for the correlation terms between normalized elevation and snow covered area which represent the effect of the sub-grid scale heterogeneity of snow covered area. The macro-scale snowmelt model which is developed in this study is applied to three mountainous basins in the central part of Japan and the results are compared with the ones from the distributed snowmelt model. Thus, the performance of the macro-scale snowmelt model is evaluated.

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Monthly mean values of the solar radiation and effective longwave radiation fluxes were estimated for 30 stations in China. With reference to the radiation data at 66 stations in Japan, the map of geographic distribution has been presented in an area of China and Japan. The solar radiation and effective longwave radiation fluxes is large in the arid region and Tibetan plateau, and small in humid regions. The net radiation fluxes were also estimated for four kinds of bare soil grounds. At a sandy ground, the amount of evaporation is small and the surface temperature is high, so the net radiation is small. At a loamy ground with a large capacity of water content, the amount of evaporation is large and the surface temperature is low, so the net radiation is large. The annual mean net radiation at a loamy ground is about 1.6 times as large as those at a sandy ground.

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Seven scenarios of global warming were simulated to estimate the effect of snowfall in winter (November - April) in Japan. Each scenario was defined as changes in air temperature and precipitation. Using previously reported values of discriminating temperature, digital maps of daily temperature and precipitation, the form of precipitation could be determined on a daily basis for the entire grid map of daily precipitation. Finally. the digital maps of monthly snowfall and rainfall under each scenario were obtained. As a result, mass of snowfall in Japan was estimated at about 131.9 billion tons for the average condition (Scenario No. 1). By increasing air temperature, the absolute value of snowfall may decrease all over Japan and ratio of snowfall to total precipitation in winter may also decrease. For the minimum case, 54.9 billion tons of snowfall was estimated (Scenario No. 7). This decrease in snowfall should result in a decrease in snowcover and snowmelt water during spring. Consequently, there may be increasing water shortages, especially in the regions which even now have low snowfall. Thus, it is necessary to estimate the effects of global warming on the water balance of watersheds in near future.

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