Challenges in calibrating hydrological models to simultaneously evaluate water resources and flood hazard: a case study of Zou basin, Benin

Under climate and land use changes, water cycle is expected to be intensified. This will likely result in frequent hydrometeorological extremes events such as droughts and floods, and affect the water balance components. A distributed model (WaSiM) was calibrated and validated to evaluate water resources and flood hazard in the Zou catchment, Benin, for the period 1991-2009. The model was calibrated and validated at a threshold of 120 m(3)/s and its performance in simulating lower discharge was evaluated. The results show that the model was able to satisfactory simulate streamflow using different thresholds with the Kling and Gupta efficiency (KGE) between 0.5 and 0.85. The model performance decreases with increasing discharge threshold. The overall water balance predicted by the model is consistent with the hydroclimatic condition of the basin. The runoff coefficient varies between 15% and 18% (11% and 14% respectively) of the total annual rainfall during the calibration (validation) period. By considering the discharge above the threshold of 120 m(3)/s the model performances were acceptable with regards to the uncertainties in discharge measurement mainly in peak discharge. Hence, the model is able to reproduce satisfactorily the hydrological processes in the study area and could be used for impact assessment.