In recent years, rainfall forecasting technologies have been advanced remarkably and some forecasts with high accuracy have been applied to dam operations practically.In this study, the accuracy of Japan Meteorological Agency' s Global Spectral Model Grid Point Value (GSM-GPV) of leading time of 192 hours at Kumano river basin and the accuracy of the efficient formulation of GSM-GPV for use of dam operations have been examined. Further, a new weather forecasting method, which combines the efficient formulation of GSM-GPV and the information about typhoons, has been proposed and tested. The results showed that the new method had the applicability to dam operations in terms of the reductions of dam flood discharge.
