JOURNAL OF JAPAN SOCIETY OF HYDROLOGY AND WATER RESOURCES

A heat balance method is used to estimate rainfall interception loss from forest canopies, and satisfactory results are obtained when the estimated interception losses are compared with experimental data.For the meteorological conditions in Japan, the ratio of the interception loss I to the annual rainfall amount P decreases as the value of P; that is, I/P_??_0.25 when P=1000mm/year and I/P_??_0.13 when P=2500mm/year.

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A basic analysis on the characrteristics of spatial distribution of monthly precipitation in the United States is resented. Monthly hydrologic quantities seem to be effective for detecting a relation between the long periodic variations of atmospheric conditions and meteorologic backgrounds in a large scale area. Data of precipitation at 176 ovservation stations in the United States for 5 years, from 1984 to 1988, was used. First, the deviation power and the spatial scales of precipitation area are defined statistically, and characteristics of the power and the scales are examined. In the next, the two-variate Gamma distribution function is applied to obataining a return period of a hydrological condition with large or small precipitation taking the spatial scale into account. At last, the relations between the spatial scales and distances between centers of high or low atmospheric pressure zones in each month in a year are also discussed.

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Evaporation control by soil-moisture movement is examined based on physical processes and is parameterized to a buckettype storage model with an impermeable bottom. Unsaturated-flow theory (Richards' Equation) was used to simulate soilmoisture movement caused by a constant potential evaporation rate. This defined the pressure-head distribution at the end of the "constant-rate stage" after which the actual evaporation would become lower than the potential rate. This distribution was approximated by a straight line, which was used to derive a relationship between potential evaporation rate and water storage obtained from the integration of the pressure-head distribution. This relationship gives the maximum evaporation rate for a water-storage value and expresses an evaporation control function by soil moisture with a storage model.

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The objective was to analyze experts' planning processes. By interviews on experts in the Tone-River basin, an expert system model was formulated which included processes such as: diagnosis of the subject region input to the system by experts, estimation of the future change in the region by the system, and selection of the best measures to improve the estimated future state following a decision tree made of various project elements arranged from rough plans in the top level to detailed ones in tail levels. The results on irrigation systems are interchanged with the agricultural development, and simultaneous analysis in two fields was enabled.

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