Past, Present, and Future Impacts of Climate Change and Variability on Flood Hazards in Sub-Saharan Africa

Abstract

Sub-Saharan Africa (SSA) is strongly affected by flood hazards, which endanger human lives and disrupt economic stability. It is therefore critical to further understand the potential impact of climate change and variability on historical and future flood hazards in SSA. To do so, we first reconstructed a complete 65-yearlong daily streamflow, presenting over 600 stations distributed throughout SSA. Using this new dataset, we found that historical trends in flood frequency, duration, and intensity were strongly modulated by decadal to multidecadal variability. We then identified internal modes of climate variability in the Pacific and Indian Oceans as primary drivers of decadal variations in flood occurrence in southern and eastern Africa. Meanwhile, decadal sea-surface temperature anomalies (SSTa) over the eastern Mediterranean region and the North Atlantic were primarily driving decadal trends in floods occurring over western and central Africa. Using 12 climate model large ensembles from the Coupled Model Intercomparison Project Phases 5 and 6 (CMIP5 and 6), we also found such decadal variations in SSTa in the Mediterranean Atlantic, Pacific, and Indian oceans could modulate the occurrence of flood hazards by up to 50% in SSA during the 21st century. Finally, combining bias-corrected CMIP6 data and the open-source hydrological model LISFLOOD, we examine the potential impact of climate change on future trends affecting the intensity, frequency, and duration of floods in West Africa. This study therefore enabled us to compare for the first time the relative importance of climate change and climate variability on future changes affecting flood hazards in SSA.