Multi-criterial validation of TOPMODEL in a mountainous catchment

The need for powerful validation methods fbr hydrological models including the evaluation of internal stages and spatially distributed simulations has often been emphasized. In this study a multi-criterial validation scheme w as used for validation of TOPMODEL, a conceptual semi-distributed rainfall- runoff model. The objective was to test TOPMODEL's capability of adequately representing dominant hydrological processes by simple conceptual approach es. Validation methods differed in the type of data used, in their target a nd in mode. The model was applied in the humid and mountainous Brugga catch ment (40 km(2)) in south-west Germany. It was calibrated by a Monte Carlo m ethod based on hourly runoff data. Additional information for validation wa s derived from a recession analysis, hydrograph separation with environment al tracers and from field surveys, including the mapping of saturated areas . Although runoff simulations were satisfying, inadequacies of the model st ructure compared with the real situation with regard to hydrological proces ses in the study area were found. These belong mainly to the concept of var iable contributing areas for saturation excess overland flow and their dyna mics, which were overestimated by the model. The simple TOPMODEL approach o f two flow components was found to be insufficient. The multi-criterial val idation scheme enables not only to demonstrate limitations with regard to p rocess representation, but also to specify where and why these limitations occur. It may serve as a valuable tool for the development of physically so und model modifications. Copyright (C) 1999 John Wiley & Sons, Ltd.