Résumé
Environmental and climatic changes have occurred in western African regions over many decades. These changes, which are variable in space and time, can have lasting effects on water resources. Hydrological modelling can help to assess the impact of these changes by representing the processes governing the relationship between climatic data and river flow regimes. This paper compares two reservoir-based hydrological models (HydroStrahler and GR4J) operating on a daily time step. The models are tested over an approx. 50-year period in a large, poorly gauged Sudano-Sahelian catchment that has undergone significant hydro-climatic variability. A calibration/validation exercise is performed using lumped and semi-distributed approaches. The simulations are compared via a multicriteria analysis based on a variety of goodness-of-fit indices. Both models simulate the rainfall runoff relationship over the catchment area with a fair degree of realism. Given the calibration strategy, the flood dynamics are better reproduced using the HydroStrahler model, while the GR4J model gives a more accurate estimate of cumulated discharge. The semi-distributed approach allows for a better representation of the hydrological processes within the watershed, which does not necessarily lead to improved outlet simulations compared to the lumped approach. A sensitivity analysis of the parameters also shows that equifinality problems are reduced when the calibration is considered within a multiobjective framework. Furthermore, the robustness of the simulations indicates that the models can be applied to various climatic conditions. The performance indexes prove satisfactory in validation periods containing either wet or dry spells. As a result, these models can be used to forecast future water availability using mid-term climatic scenarios in the basin.