Past and future spatio-temporal variability of rainfall of the Bani catchment in West Africa

Since 1970, on the Bani, main tributary of the upper Niger, annual discharges have decreased by 69% while annual rainfall has decreased only by 15% to 25% over the catchment. Among the possible causes for this very strong discharge decrease changes of precipitation patterns must be explored. Four different methods of spatial interpolation of rainfall fields were compared on intra-seasonal indices (number of dry days, the dry spells, EDI, SPI, etc.) for the period 1950-2006. This study was also conducted on simulated pluviometric data generated by a regional climatic model (WRF) for the 2032-2041 period. The pluviometric deficit is explained by a conjunction of many factors: an earlier end of rainy season, less precipitation during the core of it and an increase of the number of dry spells. The climatic model envisages an increase of annual precipitation amounts compared to the 1981-1990 period, fewer dry spells and shorter droughts.