Threshold-governed insulating and cooling effects of snow cover on alpine permafrost: evidence from the Qinghai–Tibet Plateau

Abstract

Snow cover critically influences ground thermal regimes and surface energy fluxes in alpine permafrost regions. However, its depth-dependent effects remain poorly understood, particularly on the Qinghai–Tibet Plateau (QTP), where snow is typically thin and short-lived. Using multi-year, high-resolution observations from two contrasting sites (TGL, 5100 m; XDT, 4538 m), we analyzed snow cover characteristics, ground surface temperature (GST) responses, and energy flux dynamics. Piecewise regression revealed site-specific insulation thresholds at 4.1 cm (TGL) and 6.9 cm (XDT). Above these depths, GST variability declined, the difference between GST and air temperature (ΔT) increased, and net radiation and soil heat flux decreased, indicating stronger thermal buffering. Below the thresholds, especially under snow <2 cm, GST amplitude remained high and ΔT low, suggesting enhanced cooling via albedo and melt-induced latent heat loss. Energy fluxes exhibited similarly nonlinear responses, with stronger radiative loss and variability under thin snowpacks, especially at XDT. Transient events missed by daily datasets were captured by high-frequency sensors. Compared to Arctic regions, the QTP’s snow–ground coupling is dominated by shallow-snow processes and strong surface–atmosphere exchange. These findings underscore the need for threshold-aware, depth-sensitive snow parameterizations in cold-region models to better simulate thermal transitions and permafrost responses under changing snow regimes.