Improvement of GR4J Model Applying Soil Moisture Accounting Process and Its Application in Korea Basin

Soil Moisture Accounting(SMA) process is an important topic in rainfall-runoff analysis because it determines the initial discharge in hydrological models. The SMA process is used in continuous NRCS method. However, it can not explain some events due to its assumption of initial rainfall losses. In this study, a modified SMA procedure is applied to solve the problem with the initial rainfall losses assumption of the NRCS method, and a modified GR4J model is developed using the modified SMA procedure. To verify the applicability of the proposed model, the results are compared with those from existing GR4J models in three different Korean basins. In this process, Harmony Search optimization algorithm is used to calibrate model parameters. And the calibrated parameters are verified to check the representability of the target basin. The developed model shows better results than existing models do and can improve accuracy of the rainfall-runoff model. Since the modified GR4J model shows outstanding efficiency while using less parameters, it is expected to be applied to many other Korean basins.