The streamflow series for the upstream basin of the Senegal River is marked by considerable gaps. The objective of this article is to simulate and extend hydrological data, using the GR2M rainfall-runoff model. A sensitivity analysis of the model to rainfall and water holding capacity input data was performed. This analysis was performed after calculating catchment rainfall, mean potential evapotranspiration, and maximum, minimum and mean water holding capacity. The best combination of input data was chosen by catchment based on the Nash-Sutcliffe criterion. Then cross calibration-validation tests were performed, using the selected input data to choose model parameter sets.