Although the present warning and evacuation of debris flow is determined by the amount of rainfall, it is pointed out that the volume of melting snow should be taken into consideration. The purpose of this research is, therefore, to construct a new system for the warning and evacuation from debris flow by incorporating the volume of melting snow into the present system using the amount of rainfall. In order to develop the basis of the warning and evacuation criteria of debris flows by incorporating the volume of melting snow, the authors verified the simple but accurate prediction technique for determining the volume of melting snow and investigated by measuring the soil moisture tension during the snowfall and snowmelt seasons. The results may be summarized as follows : (1) The volume of melting snow evaluated by this simple model using net radiation, air temperature and precipitation, advocated by Koike, Takahashi and Yoshino (1985), shows the same precision as the one evaluated by the heat balance model. (2) One of the characteristics of soil moisture condition during snowmelt season is that the saturated stratum had formed and continued over 10 days, due to the water supply with 30mm per day, which was observed for 13 days in April, 1998.
