Studies on the development of model to estimate the soil moisture with AMeDAS data

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The studies were conducted to develop the model to estimate the soil moisture in the root zone by using only AMeDAS data of the meteorological agency. The model is based on the water balance of the root zone and is composed by some submodels which are connected with the terms of the water balance. The outline and the experimental results on adaptability of the model are summarized as follows:Submodel to estimate the evapotranspiration was constructed by combining the Priestley Taylor method to estimate the potential evapotranspiration and the formula to calculate the net radiation from the duration of sunshine. Furthermore, to estimate the actual evapotranspiration from any surface moisture condition, the complementary relationship was available with the pan evaporation.Submodel to estimate the capillary rise was constructed by using the Darcy's law which has the unsaturated hydraulic conductivity of concerned soil and the hydraulic gradient. The hydraulic gradient was calculated by the difference of hydraulic potential between the center of the root zone and the depth of 100 cm from the center of the root zone. The hydraulic potential at the depth of 100 cm from the center of the root zone was assumed as the potential corresponded to the field capacity of the soil.Method for estimating the outflow from the root zone after the heavy rain is composed of the surface runoff and the percolation at bottom of the root zone. In this work, we could propose the method to calculate on the basis of the assumption that the soil moisture in the root zone was corresponded to the field capacity when the zero-flux layer arrived at the bottom of the root zone.Through the experiments on the adaptability of the model at the loose sloping field,the ridging field and etc., we found out that the model represented the soil moisture in the root zone fairly well.