Effects of rainfall on permafrost degradation in alpine desert regions of the Tibetan Plateau

Rainfall is increasing across the Tibetan Plateau, yet its effects on permafrost in alpine desert regions remain poorly understood. Using a validated one-dimensional land-surface model for a representative site, we conducted idealized experiments to isolate the effects of summer rainfall (SR) and extreme rainfall (ER). Increasing SR mitigated long-term permafrost degradation. ER transiently accelerated degradation during the event year but produced a long-term mitigating effect thereafter. The short- and long-term effects of ER were both modulated by background SR: as SR increased, short-term acceleration first intensified and then weakened, whereas long-term mitigation progressively declined. These responses arose from rainfall-induced changes in the surface energy balance and soil hydrothermal processes. Overall, increased SR may partly mitigate warming-driven permafrost degradation in alpine desert regions, whereas ER imposes an additional timescale-dependent effect regulated by background SR. These findings provide a mechanistic basis for interpreting rainfall–permafrost interactions across different cold region environments.