A westward shift of heatwave hotspots caused by warming-enhanced land–air coupling

Abstract

Heatwaves pose serious risks to human health and lives, but how their occurrence patterns may change under global warming remains unclear. Here we reveal a systematic westward shift of heatwave hotspots across the northern mid-latitudes around the late 1990s. Both observational analysis and numerical simulation show that this shift is caused by intensified soil moisture–atmosphere coupling (SAC) in eastern Europe, Northeast Asia and western North America under recent background warming. The strengthened SAC shifted the atmospheric high-amplitude Rossby wavenumber-5 pattern westwards to a preferred phase position, which increased the probability of the occurrence of high-pressure ridges over these 3 hotspots by a factor of up to 39. Our results highlight the importance of SAC in shaping heatwave patterns and large-scale atmospheric circulation and challenge the conventional view that the land surface only passively responds to atmospheric forcing. Heatwaves are expected to become more frequent with warming, but how their spatial patterns change is not well understood. Here the authors show that heatwave hotspots in the Northern Hemisphere have shifted westwards over the past few decades.