Projected impact of solar radiation modification geoengineering on water deficit risk over major Central African river basins

The economy of Central African countries strongly depends on rain-fed agriculture and hydropower generation. However, most countries in this subregion do not yet have the irrigation technologies that are already applied in many more advanced nations, which further exposes them to the serious risk of severe drought caused by global warming. This study investigates the potential impact of solar radiation modification (SRM) geoengineering on the water availability over the four major river basins that cross most of Central African countries (i.e., Niger Basin, Lake Chad Basin, Cameroon Atlantic Basin and Congo Basin). For this purpose a potential water availability index was computed based on an ensemble-mean simulations carried out in the framework of Phase 6 of the Geoengineering Model Intercomparison Project (GeoMIP6), considering two SRM simulation experiments: the stratospheric sulphate aerosol injection (G6sulfur) and the global solar dimming (G6solar). The climate change simulation results in a robust decreases by up to 60% in water availability, most pronounced over the Cameroon Atlantic Basin under the hight radiative forcing scenario. Therefore, in a business-as-usual world, the reduction in water availability combined with the rapid population growth expected by 2050 in the studied region, could result in a significant water deficit over Central African countries towards the end of the 21st century. This water deficit can affect all activities that depend on water resources, such as water supply, agriculture and hydropower generation. Furthermore, the results also show that SRM methods have the potential to significantly reduce this deficit by increasing water availability (as compared to climate change) by up to 50% over the affected river basins, with a more accentuated increase found in the Cameroon Atlantic Basin when the global solar dimming is applied. These results suggest good possibilities of adaptation for populations living in the geographical areas of these river basins.