Combining geospatial information and SCS-CN for surface runoff estimation in Rib watershed, upper Blue Nile Basin, Ethiopia

Surface runoff is the most significant environmental concern in the Rib Watershed. Hence, this study estimates runoff by combining geospatial information and the Soil Conservation Service Curve Number (SCS-CN) model in the watershed. Rainfall, land use, land cover, hydrologic soil group, maximum soil water retention, and CN values were processed using Arc GIS and ERDAS Imagine software accordingly. The model was validated using the coefficient of determination (R-2) and Nash-Sutcliffe efficiency (NSE). The R-2 (0.9861, 0.9508, and 0.9136) and NSE (0.7, 0.68, and 0.6) values for the periods (2018, 2020, and 2022), respectively, confirmed the good performance of the model. The result also showed runoff ranges from 497 mm/year to 1,258 mm/year. Therefore, the highest runoff is observed in most areas of Farta and Debre Tabor and in some parts of Lay Gayint, Fogera, and Kemkem districts. Consequently, this may result in a loss of soil moisture, a decline of surface and ground water, low crop yield and animal fodder, and unproductivity of the land. This, in turn, affects food security and the livelihoods of the community at large in the region. Therefore, well-planned watershed management practices should be put into practice by prioritizing runoff hotspot sites in the catchment.