Advantages of a topographically controlled runoff simulation in a soil-vegetation-atmosphere transfer model

Two methods to incorporate subgrid variability in soil moisture and runoff production into soil-vegetation-atmosphere transfer (SVAT) models are compared: 1) the variable infiltration capacity model approach (VIC), and 2) a modified "TOPMODEL'' approach. Because neither approach needs to track surface or subsurface flow within a catchment explicitly, they represent computationally efficient ways to represent hydrologic processes within the context of regional and global modeling. This study shows that, during low flow periods, the runoff simulation is superior when using the TOPMODEL-based equations, especially during the rising limb of the autumn hydrograph. A main drawback of the modified VIC-model approach, especially for regional and global application, is that, with five free parameters, considerably more model calibration is required. TOPMODEL, on the other hand, requires only the determination of one free parameter. However, a TOPMODEL approach does require extensive preprocessing of topographic data, and issues concerning resolution of the data used become relevant.