Abstract
Kamitani basin, located in the source area of Yura River, central Japan, is a snowfall region under temperate humid climate. The basin (4.9km2) is covered by natural forests of Cryptomeria japonica. Fagus crenata and Quercus mongolica var, grosseserrata. The observation duration of meteorological and hydrological data used in this study was from June 1993 to December 1994. During the observation period, the summer season climate between the two years had rather different, namely, rainy with cold in 1993, and rainless with hot in 1994. An application of a simple SVAT model based on heat balance was carried out. Three formulas based on the Jarvis (1976) model were adopted to estimate the value of surface resistance, which is one of the required parameters in the SVAT model. A runoff model was combined into the SVAT model to determine the water budget of the basin. An optimal value of minimum surface resistance could be derived after considering the water balance of the basin. From the results, the agreement of hydrograph between the calculated and observed was derived. It is clear that the value of minimum surface resistance is a changeable value with the change of climate condition even in the same basin. This phenomenon is possible to be explained using a conception of radiative dryness index. That is to say, the value of minimum surface resistance is a function of the mean soil moisture condition of a basin
