Diverse causes of extreme rainfall in November 2023 over Equatorial Africa

Abstract. Understanding the atmospheric factors that lead to extreme rainfall events is essential to improve climate forecasting. This study aims to diagnose the physical processes underlying the extreme rainfall event of November 2023 in Equatorial Africa (EA), using the ERA5 reanalysis dataset. Composite, spatio-temporal and correlation analyses are used to shed light on the relationship between the November 2023 extreme precipitation events and the various associated factors. The analysis reveals that these extreme rainfall events were mainly controlled by several factors that occurred during this period in the Pacific, Atlantic and Indian oceans. These factors include strong sea-surface-temperature (SST) anomalies in the Niño-3.4, North Tropical Atlantic, Equatorial Atlantic and Indian Ocean Dipole (IOD) oceanic regions; changes in zonal winds; the Walker circulation; the anomalous moisture flux and its divergence; the easterly jets; and the activity of the Madden–Julian Oscillation (MJO). This convergence of moisture flows entered the EA region through its western and eastern boundaries, coming from the Equatorial Atlantic and Indian oceans, respectively. The juxtaposition of these factors has led to strong and positive rainfall anomalies in EA, with the highest values over the East African region, mainly over southern Ethiopia, Somalia, Kenya and Tanzania, which received more than 430 mm of rainfall during the month. Our findings suggest that many dynamic atmospheric effects need to be taken into account jointly to anticipate this type of extreme event. The results of the present study contribute to the improvement of sub-seasonal to seasonal rainfall forecasts by the region's national meteorological services to enable us to increase the resilience of the region's citizens to these extreme weather conditions.