Unstable permafrost regions experience more severe heatwaves in a warming climate

Heatwaves are causing catastrophic consequences on natural and socioeconomic systems yet they remain under-investigated in permafrost regions. Using simulations from the Coupled Model Intercomparison Project Phase 6 (CMIP6), we present a comprehensive assessment of recent and future heatwaves across the permafrost regions of the Northern Hemisphere (PRNH). Our focus is on the characteristics of summer and winter heatwaves as well as their potential implications for infrastructure stability. Results show that the PRNH has experienced increasing heatwaves over the past decades and is projected to face more frequent and intense heatwaves, especially under higher warming levels. Globally, summer heatwaves occur more frequently, whereas winter heatwaves exhibit higher intensity, with distinct regional behaviors. Both summer and winter heatwaves in the Arctic and the Qinghai-Tibetan Plateau (QTP) occur more frequently than that in mid-latitude regions. The mid-latitudes present the strongest summer heatwaves, while the Arctic endures the most severe winter heatwaves. Historically, the Arctic and the QTP have been more affected by winter heatwaves due to their longer heatwave days and stronger intensity compared to summer heatwaves. Under warming scenarios, the Arctic is projected to continue facing greater winter heatwave pressure on account of the quick-enhancing intensity. Conversely, the QTP will be more affected by summer heatwaves due to their longer and rapidly growing heatwave days. Further analyses indicate that permafrost regions with high geohazard potential (GP) will come under greater summer heatwave stress, particularly in the Arctic and QTP, associated with longer heatwave days. The high-GP regions in Eurasia, however, are expected to bear more severe winter heatwaves driven by higher intensity. These findings deepen our understandings of heatwaves in PRNH and highlights the potential impacts of heatwaves on geohazards in permafrost regions.