The perfect storm? Concurrent climate extremes in East Africa

Abstract. Concurrent extreme climate events exacerbate adverse impacts on humans, the economy, and the environment relative to extremes occurring in isolation. While changes in the frequency of individual extreme events have been researched extensively, changes in their interactions, dependence and joint occurrence have received far less attention, particularly in the East African region. Here, we analyse the joint occurrence of pairs of the following extremes over East Africa: river floods, droughts, heatwaves, crop failures, wildfires and tropical cyclones. We use bias-adjusted impact simulations under past and future climate conditions from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP). We find an increase in the area affected by pairs of these extreme events, with the strongest increases for joint heatwaves & wildfires (+940 % by the end of the century under RCP6.0 relative to present day), followed by river floods & heatwaves (+900 %) and river floods & wildfires (+250 %). The projected increase in joint occurrences typically outweighs historical increases even under an aggressive mitigation scenario (RCP2.6). We illustrate that the changes in the joint occurrences are often driven by increases in the probability of one of the events within the pairs, for instance heatwaves. The most affected locations in the East Africa region by these concurrent events are areas close to the River Nile and parts of the Congo basin. Our results overall highlight that concurrent extremes will become the norm rather than the exception in East Africa, even under low-end warming scenarios.