Abstract
Estimating climate change impacts on water resources in West Africa has been challenged by hydrological data scarcity and inconsistencies in the available climate projections. In this study, multi-model ensembles of the most recent global and regional climate models output are used to simulate the hydrologic impacts of climate change in five major river basins (i.e. Senegal, Gambia, Volta, Niger and Chad) that comprise most of West Africa. Under Representative Concentration Pathways 4.5 and 8.5, the results consistently project substantial decreases (10 to 40%) in potential water availability across the five major river basins. The largest changes are projected to occur in the Senegal basin, Gambia basin and the Sahelian part of the other river basins. The negative trends are steepest after 2050 and in the higher greenhouse gas forcing scenario. Therefore, in a business-as-usual world, reduced water availability combined with the region’s rapidly growing population will have West Africa facing an unprecedented water deficit during the second half of the twenty-first century. However, greenhouse gas mitigation can help reduce this deficit. In the Volta basin, although potential water availability declines considerably, precipitation exceeds potential evapotranspiration during the monsoon season in both forcing scenarios, suggesting opportunities for adaptation.
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Acknowledgements
This work is entirely supported by the German Federal Ministry of Education and Research through the West African Science Service Center on Climate Change and Adapted Landuse (WASCAL). We are also grateful to the CMIP5 and CORDEX modeling centers for the generation of the projections used in this study. All the data used in this study are available at the ESGF website.
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Fig. S1
Time series of potential water availability anomalies (with respect to the reference period mean: 1976–2005) for each river basin for the historical and future climate as projected by CMIP5_Subset and CORDEX multimodel ensembles for RCP4.5 and RCP8.5. Shaded bounds the range of possible values. The vertical line denotes the end of the historical period. 10-year running mean is applied to smooth the time series. Unit is percent of reference period values (PDF 218 kb)
Fig. S2
Spatial distribution of the changes (future – reference) in water supply (precipitation) during the near future (left panels) and far future (right panels) for CMIP5 (upper panels), CMIP5_Subset (middle panels) and CORDEX (lower panels) for the RCP8.5. Outlines in bold represent the contour of each river basin (PDF 949 kb)
Fig. S3
Spatial distribution of the changes (future – reference) in water demand (potential evapotranspiration) during the near future (left panels) and far future (right panels) for CMIP5 (upper panels), CMIP5_Subset (middle panels) and CORDEX (lower panels) for the RCP8.5. Outlines in bold represent the contour of each river basin (PDF 874 kb)
Fig. S4
Annual cycle of potential water availability for historical and RCP4.5 (left panels) and RCP8.5 (right panels) for observation (i.e. CRU) and each of the CMIP5_Subset and CORDEX multimodel ensembles during the near and far future. The horizontal line indicates where ratio = 1. Above this line precipitation exceeds potential evapotranspiration (PDF 279 kb)
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Sylla, M.B., Faye, A., Klutse, N.A.B. et al. Projected increased risk of water deficit over major West African river basins under future climates. Climatic Change 151, 247–258 (2018). https://doi.org/10.1007/s10584-018-2308-x
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DOI: https://doi.org/10.1007/s10584-018-2308-x