Climate change impacts on runoff in West Africa: a review

Abstract. This review summarizes the impacts of climate change on runoff in West Africa, assesses the uncertainty in the projections and describes future research needs for the region. To do so, we constitute a meta-database made of 19 studies and 301 future runoff change values. The future tendency in streamflow developments is overall very uncertain (median of the 301 points is 0% and mean +5.2%), except for (i) the Gambia River, which exhibits a significant negative change (median = −4.5%), and (ii) the Sassandra and the Niger rivers, where the change is positive (+14.4% and +6.1%). A correlation analysis revealed that runoff changes are tightly linked to changes in rainfall (R = 0.49), and to a smaller extent also to changes in potential evapotranspiration. Other parameters than climate – such as the carbon effect on plant water efficiency, land use dynamics or water withdrawals – could also significantly impact on runoff, but they generally do not offset the effects of climate change. In view of the potential changes, the large uncertainty therein and the high vulnerability of the region to such changes, there is an urgent need for integrated studies that quantify the potential effects of these processes on water resources in West Africa and for more accuracy in climate models rainfall projections. We especially underline the lack of information concerning projections of future floods and droughts, and of interannual fluctuations in streamflow.