Projected changes in African Easterly Waves and rainfall events in West Africa with kilometre-scale global coupled simulations

Abstract. African easterly waves (AEW) are a key modulator of West African rainfall variability with impacts on tropical cyclon activity. However, climate change projections of AEW show contrasting results, underpinned by the coarseness of some simulations and the lack of consistency with surface conditions in others. Here we analyse the performance and projected changes in 3-5 day AEWs using two 30-yr long simulations consistent with historical (1990-2019) and near-future climate conditions (2020-2049) by  IFS-FESOM model at kilometer scale horizontal resolution.
We show that the model captures the spatial structure and energetics of AEW with reasonable accuracy, although it overestimates associated precipitation variability. The model projects an intensification of AEW activity over land associated with enhanced barotropic and baroclinic conversion and stronger diabatic generation of eddy available potential energy. Over the central and eastern Sahel, the model projects a shift towards more extreme rainfall events and fewer moderate ones, with an overall enhancement of rainfall. This response is not exclusively related to AEW activity, as a similar response is observed when AEW activity is low. Conversely, over the westernmost Sahel, the projected drying is related to a decrease in extreme events during AEW days and in moderate events during non-AEW days. 
Over eastern Africa, where AEWs originate, the simulated increase in the reversal of the meridional potential vorticity - caused by the increase in static stability as a response to tropical climate warming - and the enhancement of upstream convective variability set the scene for more frequent and stronger seeding disturbances for AEWs. These results underline the importance of improving AEW representation in climate models to enhance seasonal forecasting, early warning systems, and adaptation strategies in the region.