Ensemble-based CMIP5 simulations of West African summer monsoon rainfall: current climate and future changes

The West African summer monsoon (WASM) rainfall is of significant socioeconomic importance. Therefore, its response to climate change is of great concern to climate scientists. Based on observations, reanalysis, and multi-model ensemble mean (EnsMean) simulations of Coupled Model Intercomparison Project phase 5 (CMIP5) models, the responses of WASM rainfall, as well as some relevant atmospheric features, to global warming are investigated. Results from the historical period (1980–2005) indicate that EnsMean reasonably reproduced the characteristics of WASM rainfall, and the strength and position of the upper-level Tropical Easterly Jet (TEJ) and mid-level African Easterly Jet (AEJ). Under global warming, EnsMean exhibits localized future changes in spatial rainfall pattern; specifically, a statistically significant increase (decrease) is evident over the central-eastern (western) Sahel subregion. Similarly, the annual cycle exhibits a decrease (increase) in pre-monsoon (post-monsoon) rainfall over the region, evident over the Sahel subregion. Increased surface evaporation and enhanced atmospheric moisture convergence are notable over the region of increasing WASM rainfall, while a weakened and possible alteration of large-scale atmospheric circulation features is evident over the study area.