A New Method of Obtaining Surface Runoff Parameters of SIMTOP from DEM

In recent decade the TOPMODEL concept has been widely adopted in soil-vegetation-atmosphere transfer (SVAT) schemes for addressing hydrological response over the land surface. However, the traditional method for determining the parameters involved in the land surface process parameterizations with TOPMODEL concept was inaccurate and complex. Although a simple TOPMODEL-based surface runoff parameterization scheme (SIMTOP) aimed to resolve this problem has been proposed, the determination of some specific parameters was subjective and still need to be improved. This study presented an improved surface runoff scheme to replace original , in which parameters a and b can be easily derived from topographic indices using the least squares method. For evaluating the performance of the improved SIMTOP, three watersheds located in climatically typical warm humid and arid, semi-arid areas, namely the Youshuijie, Hanzhong and Yingluoxia catchments were chosen for the purpose. The results indicated that the fitting curves of topographic indexes with new scheme was much closer to actual distribution curves than that obtained by the original SIMTOP and the three-parameter gamma distribution function scheme; and in arid and semi-arid areas, the improved SIMTOP performs evidently better than the old ones. The improved SIMTOP is applicable both to watershed hydrological simulations and to regional and global climate studies.