Evaluation of the Function of Forest for Rainwater Discharge in the Sado Island

In order to numerically evaluate the water discharge property of the two watersheds in the Ookura River located at the Sado Island, we apply the Hydrologic cycle model (HYCYMODEL) to the discharge response to rainfall observed in the forest catchment and the grass catchment. The parameters in this model are optimized by the trial and error method. Adaptability of the HYCYMODEL to observed discharge is fairly good for 6 years in the snowless periods. The ratio of infiltrating area to total catchment area and baseflow discharge are large in the forest catchment. So, the water storage capacity in the forest catchment is large compared with that of the grass catchment.