Quantifying the impacts of increasing light and moderate rainfall on permafrost thermal regimes over the Qinghai-Tibet Plateau: A controlled sensitivity study

• Light and moderate rainfall each contribute ∼40 % of summer precipitation on the QTP and exhibit contrasting spatial patterns. • Increased light and moderate rainfall reduce net ground heat input and cool the active layer, with the strongest effects in dry zones. • In dry areas, 10 mm of light rainfall induces stronger cooling, reducing ALT and TTOP by 0.07 m and 0.04 °C, compared with 0.05 m and 0.03 °C for moderate rainfall. Permafrost degradation is accelerating worldwide as climate warming intensifies, and air temperature is widely recognized as the dominant driver of permafrost thermal changes. In contrast, the role of rainfall, which exhibits strong temporal and spatial variability, remains poorly quantified. In this study, a permafrost-adapted land surface model to was used to quantify the effects of summer light and moderate rainfall on permafrost thermal regimes across the Qinghai-Tibet Plateau. Light and moderate rainfall each contribute approximately 40 % of summer precipitation but display distinct spatial distributions, with light rainfall prevailing dry regions and moderate rainfall dominating wetter areas. Simulation results indicate that increases in both rainfall types enhance latent heat flux while suppressing sensible and ground heat fluxes, thereby reducing net soil heat input and inducing widespread cooling within the active layer and near-surface permafrost. Cooling is most pronounced in dry areas and within the upper ∼3 m of the soil profile. For equivalent precipitation increases, light rainfall produces a stronger cooling response than moderate rainfall. Specifically, a 10 mm increase in light rainfall reduces active layer thickness and temperature at the top of permafrost by 0.05 m and 0.03 °C, respectively, compared with corresponding reductions of 0.04 m and 0.02 °C for moderate rainfall. Derived from a controlled sensitivity experiment designed to isolate rainfall effects, these results highlight the importance of explicitly accounting for rainfall type, intensity, and spatial variability in permafrost assessments. The findings further demonstrate that frequent light rainfall can partially offset permafrost warming in arid alpine environments.