COMPARISON OF SIMPLE VERSUS COMPLEX DISTRIBUTED RUNOFF MODELS ON A MIDSIZED SEMIARID WATERSHED

The increasing availability of distributed rainfall data and computati onal resources is providing the opportunity to use distributed models for rainfall-runoff forecasting or other applications. This paper comp ares the accuracy of simulations from a complex distributed model (KIN EROS), a simple distributed model (based on the Soil Conservation Serv ice (SCS) method), and a simple lumped model (SCS method). The 150 km2 , semiarid Walnut Gulch experimental watershed was the test site; mode ls were validated using 24 severe thunderstorms and rain gauge densiti es similar to those found at flash flood warning sites (one gauge per 20 km2). Under these circumstances, none of the models were able to ac curately simulate peak flows or runoff volumes from individual events. Models showed somewhat more skill in predicting time to peak and the ratio of peak flow to volume. When calibration was performed, the accu racy of the complex distributed model was similar to that of the simpl e distributed model. Without calibration, the complex distributed mode l was more accurate than the simple distributed model. The spatially l umped model performed very poorly. The complex distributed model was v alidated under real-time forecasting conditions; forecasts based on ob served rainfall had lead times of 30-75 min.