Résumé
West Africa has been greatly affected by runoff decrease since the 1970s, which is mainly explained by a decline in rainfall. However, the catchments' sensitivity to this decrease is variable and controlled by complex processes. Physically-based modelling aims at representing the interactions between external factors (rainfall and temperature) and internal factors in the catchment (land-use, soil and groundwater). The SWAT agro-hydrological model was operated at a daily time step during 1952-2000 in the Bani catchment (100 000 km(2), Mali). The modelling implies a preliminary constitution of spatial data (rainfall, temperature, land-use, soils and sub-basin delineation) in a resolution and an accuracy adapted to the simulation objectives and to the data availability. The model has a certain physical realism in the representation of the soil vegetation atmosphere interactions. It also leans on empirical parameters concerning runoff, groundwater and channel flow. The empirical parameters are calibrated to optimize the simulated daily discharge at the catchment's outlet. The validation is made over various periods and in various gauging stations. The calibration/validation results are satisfactory at the catchment's outlet (Nash coefficients values reaches 0.88 for calibration, and from 0.81 to 0.91 for validation) but also in various gauging stations located in tributaries (Nash coefficients values range from 0.70 to 0.85). The model could be used to better understand the role and the hierarchy of the control factors of flows over this large tropical catchment. It also allows for the spatialization the water flow. It can therefore constitute a support for the estimation of the variability of surface water resources in these vulnerable tropical areas.