Classification of flood-generating processes in Africa

Floods have large impacts on the populations and the economy of Africa, but little is known about the dominant flood generating mechanisms across this continent. This study is based on a large set of African basins, with the aim of identifying the main mechanisms causing floods. A total of 13815 flood events between 1981 and 2018 in 529 catchments are classified to identify the main flood drivers in different African regions. The classification is based on daily river discharge data together with precipitation and soil moisture from the ERA5-Land reanalysis, to identify flood events associated with short rains, long rains, or excess rain over saturated soils. Results indicated that processes related to soil saturation, either before floods or during long rainfall events, are strongly associated with the occurrence of floods in Africa. Excess rain in Western Africa, and long rain for catchments in Northern and Southern Africa, are the two dominant generating mechanisms, contributing to more than 75% of all flood events. Overall, no significant changes were detected in the relative importance of these drivers over the last decades. The major implication of these results is to underline the importance of soil moisture dynamics, in addition to precipitation intensity, to analyze the evolution of flood hazards or implement flood forecasting systems.