Comparing CFSR and conventional weather data for discharge and sediment loss modelling with SWAT in small catchments in the Ethiopian Highlands

Abstract. Accurate rainfall data is the key input parameter for modelling river discharge and sediment loss. Remote areas of Ethiopia often lack adequate precipitation data and where it is available, there might be substantial temporal or spatial gaps. To counter this challenge, the Climate Forecast System Reanalysis (CFSR) of the National Centers for Environmental Prediction (NCEP) readily provides weather data for any geographic location on earth between 1979 and 2010. This study assesses the applicability of CFSR weather data to three watersheds in the Blue Nile Basin in Ethiopia. To this end, the Soil and Water Assessment Tool (SWAT) was set up to simulate discharge and sediment loss, using CFSR and conventional weather data, in three small-scale watersheds ranging from 102 to 477 ha. Uncalibrated simulation results were compared to observed river discharge and observed sediment loss over a period of 25 years. The conventional weather data resulted in satisfactory discharge outputs for all three watersheds, while the CFSR weather data resulted in unsatisfactory discharge outputs for two of three gauging stations. Sediment loss simulation with conventional weather inputs yielded satisfactory outputs for all three watersheds, while the CFSR weather input resulted in one very good result and two unsatisfactory results. Overall, the simulations with the conventional data resulted in far better results for discharge and sediment loss than simulations with CFSR data. The simulations with CFSR data were unable to adequately represent the specific regional climate for the three watersheds, performing even worse in climatic areas with two rainy seasons. Hence, CFSR data should only be used with caution in remote areas with no conventional weather data and might be better adapted to larger watersheds than the ones used in this study.