Amplification of Mega-Heatwave Temperatures by Upwind Drought Conditions

Heatwaves have become increasingly frequent, are not only responsible for many deaths related to natural disasters across the globe, but also cause agricultural and economic losses, and thus take a considerable toll on society. Local drought conditions have been shown to exacerbate heatwave temperatures, particularly in the presence of atmospheric blockings, but the effect of remote land surface conditions has not received much attention by the scientific community yet. Here, we quantify the impact of upwind drought conditions on the evolution of air temperatures during the European mega-heatwaves in 2003 and 2010. We use the Lagrangian parcel trajectory model FLEXPART in conjunction with reanalysis and satellite data from 1980–2016 to trace the origin of heat and disentangle the effects of local and remote land surface conditions on the local heat budget. Our results show that, during both mega-heatwaves, nearly one third of the total advected sensible heat was caused solely by the desiccated soils upwind. Together, persistent atmospheric circulations and the upwind droughts fostered conditions for anomalously high temperatures during both heatwaves. In the face of subtropical drought aggravation and global warming, our research has implications not only limited to the western Eurasian midlatitudes and highlights the potency of compound drought–heatwave events.