Extreme rainfall reshapes permafrost thermal regimes across the Northern Hemisphere

Extreme rainfall events can significantly alter the thermal and hydrological dynamics of the active layer in permafrost regions, potentially accelerating permafrost degradation and amplifying climate warming. However, how regional climatic conditions regulate the direction and intensity of soil temperature responses to extreme rainfall remains poorly understood. In this study, we integrated four extreme rainfall indices and employ three analytical approaches to quantify the effects of extreme rainfall across 131 permafrost sites in the Northern Hemisphere. Principal component analysis was further applied to identify distinct soil thermal response patterns to extreme rainfall. Our results show that rain generally cools the shallow soil layers, while warming deeper layers. We further find that extreme rainfall cools permafrost in humid regions, where the land surface has been disturbed, and where ground ice and soil organic matter is low. Conversely, in arid regions, shrub-dominated landscapes, and where ground ice content and soil organic matter are high, permafrost is warmed by precipitation. These findings suggest that extreme rainfall can be a major driver of permafrost change, capable of accelerating active-layer thaw. Because the direction and magnitude of these effects depend strongly on regional climate and ecosystem characteristics, future permafrost projections must explicitly account for rainfall extremes rather than relying primarily on air temperature trends. As extreme precipitation events become more frequent, the resulting warming in ice- and carbon-rich regions may heighten risks of ground subsidence and carbon release, amplifying climate-change feedbacks.