Analysis of projected compound climate extremes across two major river systemsin South Africa

Projected increases in temperature and alterations in precipitation patterns across two major river systems in South Africa necessitate the implementation of adaptation strategies to address water scarcity and flood hazards. The Integrated Vaal River System (IVRS), the primary freshwater supply system for Johannesburg, is increasingly challenged by extreme drought conditions, and the coastal rivers, including the Umgeni, Mlazi, and Mbokodweni rivers, east of the Lesotho highlands in the Greater Durban region, face significant flood risks. To develop adaptation measures, compound climate extremes, such as coincident or sequential meteorological droughts and heatwaves, as well as meteorological droughts followed by extreme precipitation, are of particular interest.

In the present study, the focus is on the changes in frequency and spatial distribution of coincident and sequential compound climate extremes across both river systems. Using the bias-adjusted CORDEX-CORE Africa climate RCP8.5 projection ensemble at a 0.22° spatial resolution, generated by three regional climate models that dynamically downscaled three distinct Earth system models, enables a comprehensive assessment of model uncertainties. Initial results indicate that the occurrence of coincident meteorological droughts and heatwaves increases along a south-to-north gradient, with longer durations over the IVRS toward the end of the century. This research is conducted in the WaRisCo project, which is a part of the “Water Security in Africa – WASA” programme.