Climate change impacts on runoff in West Africa: a review

Abstract

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.

The Impact of Climate Change on Water Resource Availability in a Trans-Boundary Basin in West Africa: The Case of Sassandra

“…However, an assessment of water resources from Guinea, the West African water tower, with a distributed hydrological model could refine this assessment in the actual and future socio-economic development context in Guinea. The obtained discharges change using the equation of Roudier et al [41], are almost similar to the values obtained by Bio [47] in Ouémé River Basin in Benin (West Africa). He observed discharges decreasing between −15% to −37% using the climate scenarios RCPs 4.5 and 8.5 rainfall data simulated by two regional climate models (DMI-HIRHAM5 and SMHI-RCA4).…”

“…We estimated the variation of this quantity based on the results of Roudier et al [41]. Indeed, according to the study, the change in runoff is a function of the variation in precipitation in the Sassandra Basin according to Equation (5).…”

“…The results indicated that, for RCP 4.5, the variation will be −48. Even if this evaluation was roughly estimated, it provides an indication of the evolution of this parameter until 2090, which must be taken with some precaution given that the equation of Roudier et al [41] (used for the assessment) was determined for the entire basin and not for a part of the basin. However, an assessment of water resources from Guinea, the West African water tower, with a distributed hydrological model could refine this assessment in the actual and future socio-economic development context in Guinea.…”

Land Use and Land Cover Changes under Climate Uncertainty: Modelling the Impacts on Hydropower Production in Western Africa

“…The increase of temperature over West Africa during the end of the 20th century induced an increase of potential evaporation, which might reduce the runoff. However, the joint effect of climate change and human activities on land cover over more than three decades is responsible for an increase of the runoff coefficients of the Black Volta basin, despite the low rainfall variability observed during the data analysis [31,32]. The runoff coefficients have increased and is projected to increase in Black Volta basin according to scenario of LCC and CC.…”

Future Climate Change Impacts on Streamflows of Two Main West Africa River Basins: Senegal and Gambia

“…The severity and the magnitude of the impact depend on the geographical area and context. In West Africa, Roudier et al [15] summarized different funding related to the impact of climate change on water resources. Overall, a decrease of rainfall going from 20% to 30% was noticed, which led to a decrease in river flows ranging from 40% to 60% [5].…”