Rainfall-runoff processes of Koupendri catchment north-west, Benin: a modeling approach.

This study calibrated and validated rainfall-runoff model (WaSiM) to aid decisions on sustainable management of scarce water resources in Koupendri catchment. Data on soils and soil hydrological properties in combination with land use and short-time series data of climate and discharge were used for the calibration and validation of WaSiM model. The most sensitive parameters of soil and land use parameters were identified and optimized. The model was successfully calibrated (NSE= 0.61; R²=0.61, RMSE= 0.63) and validated (NSE= 0.68; R²= 0.78; RMSE= 0.57) for the catchment. Though the model underpredicted some of the peak flows, the overall calibration result can be adjudged satisfactory with a p-factor of 0.94 and an r-factor of 0.93 which are all within the acceptable range of uncertainty. Evapotranspiration and discharge constituted 98%–99% of the total water balance of the catchment while the change in soil moisture storage constituted only < 2%. Surface runoff was the predominant streamflow component (86%–90%), suggesting infiltration excess overland flow as the main runoff generation mechanism for the catchment. The water balance reflected the hydro climatic conditions of the catchment with actual evapotranspiration ranging between 68% and 75% of the total annual rainfall.