Résumé
The problem of using data outputs from general circulation models (GCMs) to assess the impacts of climate change on runoff in West Africa is addressed. The annual and monthly precipitation data from four GCMs used in the Third Assessment Report of the IPCC were studied over the 1950-1998 period: the CSIRO-Mk2, ECHAM4, HadCM3 and NCAR-PCM models. Two weaknesses common to all these models are their inability to reproduce rainfall volumes in the Sahelian zone, and their difficulty in simulating the seasonal dynamics of rainfall in the Guinean zone. Two climate scenarios were then developed based on the changes predicted by the HadCM3-A2 model, which aimed to generate time series for rainfall and potential evapotranspiration up to the end of the 21st century, in order to simulate probable future climatic conditions. These scenarios were used as input to the hydrological model GR2M to assess the impacts of climate change on the discharge of four main rivers: the Senegal, the Gambia, the Sassandra and the Chari. The results show that the possible future changes in runoff are highly dependent on rainfall and, hence, on the quality of the output of a given GCM.