Near-term impacts of climate variability and change on hydrological systems in West and Central Africa

Climate change is expected to significantly impact on the availability of water resources in West and Central Africa through changes in rainfall, temperature and evapotranspiration. Understanding these changes in this region, where surface water is fundamental for economic activity and ecosystem services, is of paramount importance. In this study, we examine the potential impacts of climate variability and change on hydrological systems by the mid-21st century in West and Central Africa, as well as the uncertainties in the different climate-impact modelling pathways. Simulations from nine global climate models downscaled using the Rossby Centre Regional Climate model (RCA4) are evaluated and subsequently bias-corrected using a nonparametric trend-preserving quantile mapping approach. We then use two conceptual hydrological models (GR2M and IHACRES), and a regression-based model built upon multi-timescale sea surface temperatures and streamflow teleconnections, to understand hydrological processes at the subcontinental scale and provide hydrological predictions for the near-term future (2020–2050) under the RCP4.5 emission scenario. The results highlight a zonal contrast in future precipitation between western (dry) and eastern (wet) Sahel, and a robust signal in rising temperature, suggesting an increase in potential evapotranspiration, across the multi-model ensemble. Overall, across the region, a significant increase in discharge (~ + 5%) is expected by the mid-21st century, albeit with high uncertainties reported over most of Central Equatorial Africa inherent to climate models and gridded observation data quality. Interestingly, in this region, teleconnections-based regression models tend to be an alternative to hydrological models.