Soil moisture was observed in situ for three years (1992-1994) to compare the effect of different vegetations (forest, grassland and wheat field) on soil moisture under the same meteorological conditions. The observation sites were located in a boreal humid climate where snow covers for about four months annually. The soil moisture was measured by the heat-probe method (Kasubuchi, 1992). It could measure the soil moisture automatically and continuously even under the snow covered condition. Seasonal variations of the soil moisture was characterized into three stages; from thawing to active vegetation (spring to summer), rainy (autumn) and snow covered (winter) period. The soil moisture and temperature were much influenced by the active time and the root system of each vegetation. Differences in soil moisture among the years depended on the meteorological conditions which affected the vegetation growth. From these observations, it became clear that the soil moisture and the soil temperature were affected not only by meteorological conditions but also by the vegetations.

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The interannual variability of water balance in Balkhash lake basin, the closed lake located in Central Asia, is investigated by using precipitaion and runoff data over long-term period. The interannual variability of the lake area estimated with satellite data by previous study is also compared with the results of this study. Due to the completion of Kapchagay reservoir in the middle reach of Ili river which accounts for the 80% of total inflow into the lake. Balkhash lake has been diminishing after 1970, reflecting man-made discharge control. In addition, natural decreasing trend appeared in the discharge of the upper reach of Ili river is also responsible for the diminishing of the lake. The absolute value of the lowering of the lake level and the diminishing rate after 1970 are found to be within the range of natural variability.

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An experimental study of estimating the bulk transfer coefficient and the surface moisture availability in the paddy field is presented. The results are as follows: (1) The bulk transfer coefficient of the paddy field as one layer that was estimated for every two or four hours fluctuated, while daily average value was close to that calculated by the multilayer model of Kondo & Watanabe. (2) The surface moisture availability of the paddy field as one layer was higher in the morning, lower in the afternoon and higher when it was cloudy or the humidity was higher, and inversely correlated to wind speed. The surface moisture availability of the rice canopy was lower than that of the one layer and the variational tendency was similar to that of the one layer. (3) The wet imitation leaf method was supposed to estimate well the ratio of the leaf transfer coefficient for latent heat and sensible heat because the leaf temperature was close to that of actual leaf. (4) The result of estimating the daily latent heat flux by one layer or two layers models showed no superiority because the surface moisture availabilities of both models changed hourly. For the application of each model, the variational tendency of the surface moisture availability should be studied further.

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The research on optimum dam water supply control has more than one-century history since the adaption of mass-curve. Nowadays, old fashioned mass-curve rule is mostly out of use and dynamic programming (D.P.) or such kind of high-level computer calculation models are mainly used for the research. But these high-level models are not used for actual dam control, because they require huge computer calculation volume and are hard to understand for engineers working in dam operation office. Consequently, there is no optimum dam water supply control model for practical use in dam operation offices at present. However, when future inflow is given beforehand, one useful theory for optimum dam water supply control is doubtlessly existing. This theoretical method does not need any high-level complicated calculation and is easy to use by engineers in general. This fact is not known to the engineers around the world in correct meaning, so that this paper explains the theory and its calculation method for practical use.

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The authors have reported previously using an estimation method of air temperature that the mitigation effects of vegetation regarding air temperature for surface boundary layer increase linerly with NDVI. The mitigation effects of vegetation are evaluated in this paper by comparing air temperatures at six locations of AMeDAS in Shimane Prefecture, where the meteorological conditions are the same and the values of NDVI at those sites are different. The evaluation method is for comparing the maximum air temperatures at six AMeDAS stations on clear days to eliminate the effects of clouds as regards air temperature. The spring and summer seasons were selected so that the transpiration from the vegetation could cause the mitigation effects. The estimation method was certified since the value of the mitigation effects coincides with the result through the estimation method. The decrease in the maximum air temperature due to the vegetation effects resulted in more than 5°C for the increase of 0.7 in NDVI.

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It was already confirmed that a local equilibrium exists between the vapor and liquid phases of water in soils with a good degree of approximation under natural conditions (Milly, 1982). In the present paper, it is shown that the equilibrium can be regarded to exist also at and near the soil surface during evaporation. This result suggests that the experimental formulas proposed to be used in numerical weather-climate models to estimate the 'soil surface humidity' from the water content at the surface are not the replacements to the thermodynamic equilibrium formula (Eq. (7) in the present paper) (Lee and Pielke, 1992) but mere empirical formulas without much physical meaning, because they are greatly influenced by the resistance to vaper movement near the surface.

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