Global relevance of atmospheric and land surface drivers for hot temperature extremes

Hot temperature extremes have severe impacts on society and ecosystems. These extremes are driven by both atmospheric and land surface processes, such as advection or reduced evaporative cooling. The contributions of the individual drivers to the formation and evolution of hot extremes have been analyzed in case studies for major past events, but the global relevance of drivers still remains unclear. In this study, we determine the relevance of (i) atmospheric drivers, such as wind, geopotential height, horizontal geopotential height differences, and surface net radiation, and (ii) land surface drivers, such as evaporative fraction and enhanced vegetation index, for hot extremes across the globe using observation-based data. Hot extremes are identified at daily and weekly timescales through the highest absolute temperature, and the relevance of the considered drivers is determined with an analogue-based approach. Thereby, temperature anomalies are analyzed from situations with driver values similar to those of the hot extreme. The results show that geopotential height at 500 hPa is overall the most relevant driver of hot extremes across the globe at both timescales. Surface net radiation and evaporative fraction are the second most relevant drivers in many regions at the daily timescale, while wind is the second most relevant at the weekly timescale. Regional variations in the relevance of individual drivers are largely explained by different climate regimes. Revealing key regions and influential timescales of land surface drivers on hot extremes can inform more efficient prediction and management of the increasing threat these extremes pose.