Long-term hydrologic simulation using SCS-CN-based improved soil moisture accounting procedure

The Soil Conservation Service Curve Number (SCS-CN) method is widely used in determination of direct surface run-off in long-term (continuous) hydrologic simulation models. Of late, Michel et al. (2005) reviewed the soil moisture accounting (SMA) procedure that lies behind the original SCS-CN method and pointed out severe structural inconsistencies in the treatment of antecedent condition and, in turn, proposed a sounder methodology. However, this method still needs refinement in the definition of initial moisture level (V-0) to make it usable in field. Thus, in the present study, the Michel et al. (2005) model is modified to avoid the unrealistic sudden jump in V-0 by incorporating conceptual SMA procedure and variation of daily CN based on antecedent moisture amount instead of antecedent moisture condition. When applied to 17 watersheds from different agro-climatic regions of India, the proposed model simulates daily stream flows better than those due to Michel et al. model. The proposed model performed better in high run-off producing (wet) watersheds than in low run-off producing (dry) watersheds, and the base flow was more and less significant in high and low run-off producing watersheds, respectively, whereas the evapotranspiration showed a reverse trend. Copyright (C) 2010 John Wiley & Sons, Ltd.