Present and Future of Heavy Rain Events in the Sahel and West Africa

Abstract

Gridding precipitation datasets for climate information services in the semi-arid regions of West Africa has some advantages due to the limited spatial coverage of rain gauges, the limited accessibility to in situ gauge data, and the important progress in earth observation and climate modelling systems. Can accurate information on the occurrence of heavy precipitation in this area be provided using gridded datasets? Furthermore, what about the future of heavy rain events (HRE) under the shared socioeconomic pathways (SSP) of the Inter-Sectoral Impact Model Intercomparison Project (i.e., SSP126 and SSP370)? To address these questions, daily precipitation records from 17 datasets, including satellite estimates, interpolated rain gauge data, reanalysis, merged products, a regional climate model, and global circulation models, are examined and compared to quality-controlled in situ data from 69 rain gauges evenly distributed across West Africa’s semi-arid region. The results show a consensus increase in the occurrence of HRE, between observational and gridded data. All datasets showed three categories of HRE every season, but these categories had lower intensities and an overstated frequency of occurrence in gridded datasets compared to in situ rain gauge data. Eight out of 17 databases (~47%) show significant positive trends and only one showed a significant negative trend, indicating an increase in HRE for all categories in this region. The future evolution of HRE considered under the shared socioeconomic pathways SSP1-2.6 and SSP3-7.0, showed a trend toward the intensification of these events. In fact, the mean of the ensemble of the models showed significant changes toward higher values in the probability distribution function of the future HRE in West Africa, which may likely trigger more floods and landslides in the region. The use of gridded data sets can provide accurate information on the occurrence of heavy precipitation in the West African Sahel. However, it is important to consider the representation of heavy rain events in each data set when monitoring extreme precipitation, although in situ gauge records are preferred to define extreme rainfall locally.

Understanding the Regionality of Extreme Rainfall in the Sahel: The Mali Hotspot

“…West African Sahel extreme rainfall events have changed over the past 40 years. There has been a significant increase in their frequency (Chagnaud et al 2022;Saley and Salack 2023) as rainfall producing storms have become more intense and better organized (Taylor et al 2017;Tramblay et al 2020;Klien et al 2021). Flooding has increased as the storms become more frequent and destructive (Elagib et al 2021;Fofana et al 2022;Chahinian et al 2023), although some of the increase in flood disasters is associated with landuse/landcover changes associated with a quickly growing population (Sougué et al 2023).…”

“…[Over the last 40 years, the population of the West African Sahel nations of Senegal, Gambia, Mauritania, Mali, Burkina Faso, and Niger has increased from around 27 million in 1979 to 92 million in 2021 (United Nations 2022)]. These changes in storm intensity and frequency are projected to continue (Han et al 2019;Kendon et al 2019;Fitzpatrick et al 2020;Saley and Salack 2023).…”