Solar Geoengineering Potential in Flood Assuagement in Four East African Cities

This study evaluates the potential of solar radiation management (SRM) to mitigate projected increases in rainfall and flood risk across four major urban centers in Eastern Africa. Flood dynamics under historical and future climate conditions were simulated using the Rainfall–Runoff–Inundation (RRI) model. Observed hydrological conditions were established using daily precipitation from the Climate Hazards Group Infrared Precipitation with Stations (CHIRPS), together with hydrological and topographic datasets. Future flood projections and associated impacts were derived from climate simulations produced by the Whole Atmosphere Community Climate Model version 6 (WACCM6) and solar climate intervention experiments from the Assessing Responses and Impacts of Solar climate intervention on the Earth system with Stratospheric Aerosol Injection (ARISE-SAI) framework, both forced by the Shared Socioeconomic Pathway SSP2-4.5. Model performance was evaluated using the Nash–Sutcliffe efficiency (NSE), coefficient of determination (R2), root mean square deviation (RMSD), and peak discharge error (PDE). The RRI model reproduced observed river discharge with reasonable skill, exhibiting lower RMSD and PDE values for the Ethiopian catchment compared to those in Kenya and Tanzania. Results indicate that SRM implemented through stratospheric aerosol injection (SAI) can reduce peak inundation depths and the spatial extent of flooding in selected flood-prone areas of Dar es Salaam and Addis Ababa. These reductions correspond to a decrease in the projected exposure of populations and critical infrastructure to flood hazards. While the findings suggest that albedo-based solar geoengineering may moderate flood impacts in some Eastern African cities, uncertainties remain, particularly in the representation of convective rainfall processes and the reliance on a single hydrological modeling framework in this study. Further research using improved climate simulations and ensemble-based hydrological approaches is recommended.