Wet‐Bulb Temperature Extremes Locally Amplified by Wet Soils

Abstract Wet‐bulb temperature extremes (WTEs) occur due to a combination of high humidity and temperature, and are hazardous to human health. Alongside favourable large‐scale conditions, surface fluxes play an important role in WTEs; yet, little is known about how land surface heterogeneity influences them. Using a 10‐year, pan‐African convection‐permitting model simulation, we find that most WTEs have spatial extents 2,000 . They occur preferentially over positive soil moisture anomalies (SMA) typically following rainfall. The wet‐bulb temperature is locally amplified by 0.5–0.6C in events associated with smaller‐scale SMA (50 km across) compared to events with larger‐scale SMA (300 km across). A mesoscale circulation, resulting from stronger spatial contrasts of sensible heat flux, more efficiently concentrates moist, warm air in a shallower boundary layer. This mechanism could explain the underestimation of peak Twb values in coarser‐resolution products. The role of antecedent SMA from recent rainfall may help issue localized early warnings.