Water resources management in West Africa faces a dual challenge: the climatic deterioration observed since the 1970s and the lack of high-quality hydrological data. This study is part of the IRN ActNAO project, which aims to revise West African hydrological standards. The objective is to determine the minimal information required to simulate streamflows in poorly gauged catchments using the GR4J model. The study focuses on six sub-basins of the Gambia and Senegal rivers. The datasets used include observed rainfall, satellite precipitation (TAMSAT), temperature (for PET estimation), and streamflow. A moving calibration/validation approach is applied with time series ranging from 2 to 20 years. The KGE index is used to evaluate model performance. Results show strong robustness during calibration, regardless of the data source. In validation, performances are more variable, with the best results obtained in the Bafing sub-basins. Unexpectedly, TAMSAT data outperform observed rainfall. A five-year TAMSAT series is sufficient to properly calibrate the model. These findings highlight the potential of satellite data to overcome the lack of ground observations and also provide a useful basis for hydraulic infrastructure design and sustainable water resources management in West Africa.