In the context of global warming, understanding the impact of thaw slump on soil hydrothermal processes and its responses to climate is essential for protecting engineering facilities in cold regions. This study aimed to investigate the effect of thaw slump development on active layer soil. We considered the early thaw slump development in the Tibetan Plateau as research object and conducted long-term monitoring of soil hydrothermal activity in the active layer of various parts of the landslide and the regional meteorology. The results showed that thaw slump development shortened the freezing and thawing time of the active layer, increased the freezing and thawing rates of the shallow soil (10-20 cm), and enhanced the heat exchange between the active layer soil and the atmosphere and the heat transfer between the soils. The heat-exchange efficiency of the active layer, from largest to smallest, was headwall > collapsed area > unaffected area (bottom of the slope) > unaffected area (top of the slope). Furthermore, thaw slump development lowered the water storage of the active layer prof ile and weakened the dynamic response of soil water to precipitation. The events of soil water responses and soil water increments were smaller in the landslide area than in the unaffected area. During a co-precipitation event, the overall soil water storage increment (SWSI) of the profile was significantly smaller in the landslide area than in the unaffected area (P < 0.05), with an SWSI of 2.04 mm in the headwall and 1.77 mm in the collapsed area. In addition, thaw slump development altered the mechanism of soil water transport driven by soil temperature changes, which affected soil water redistribution of profile. The study gives ecohydrology-related research in cold climates a scientific foundation, thereby guiding the construction and maintenance of infrastructure projects.

Accurate understanding and modeling of soil hydrothermal dynamics in permafrost regions is essential for reliably assessing future permafrost changes and their impacts. However, the inadequate representation of soil water-heat transport processes in current land surface models (LSMs) introduces large uncertainty in simulating permafrost dynamics, particularly on the Qinghai-Tibet Plateau (QTP). In this study, we modified the parameterizations of soil thermal conductivity, unfrozen water and soil evaporation resistance in version 5.0 of the Community Land Model (CLM5.0) and assessed their effects on soil hydrothermal dynamics in permafrost regions on the QTP using in-situ measurements the depths of 10-40 cm. The results showed that soil temperature was more sensitive to the modified soil thermal conductivity and unfrozen water schemes, with average RMSE reduced by approximately 0.60 degrees C compared to the default CLM5.0. Soil moisture was mainly affected the unfrozen water scheme during freezing and by the optimized soil evaporation resistance scheme during thawing, with maximum accuracy improvements of 8% and 25%, respectively. All three schemes significantly improved soil thermal conductivity simulations, reducing RMSE over 80%. Overall, our modifications remarkably reduced simulation errors compared to the default schemes, improving the average accuracy soil temperature, soil moisture and soil thermal conductivity by approximately 16%, 21% and 81% respectively. Additionally, this study emphasized the importance of accurately representing permafrost-related processes in LSMs, as they significantly affected simulation results. Specifically, soil thermodynamics is strongly sensitive to subtle changes in soil moisture transport processes, such as the hysteresis effect unfrozen water content, and parameterizations of snowpack and vegetation. Therefore, future work should focus on enhancing the accurate representations of these processes and optimized parameters in LSMs to improve the simulation accuracy in permafrost regions on the QTP. This study enhanced the understanding of soil hydrothermal processes in LSMs and provided valuable insights for the future model development for permafrost regions under the context of climate change.

The Qinghai-Tibet Plateau (QTP) has experienced rapid environmental changes, including climate warming and wetting, since the 1980s. These environmental changes significantly impact the shallow soil hydrothermal conditions, which have key roles in land-atmosphere feedback and ecosystem functions. However, the spatial variations and responses of soil hydrothermal conditions to environmental changes over the QTP with permafrost (PF) and seasonal frost (SF) remain unclear. In this study, we investigated the spatial variations in soil temperature (ST) and soil moisture (SM) changes over the QTP from 2000 to 2020 using 99 in-situ sites with observations at 4 depths (i.e. 10, 40, 100 and 200 cm). The main environmental controlling factors were further identified using a calibrated statistical model. Results showed that significant ( p < 0.05) soil warming occurred at multiple soil layers during 2000-2020 with a wide variation (i.e. 0.033-0.039 degrees C per year on average), whereas the warming rates at PF sites were two times greater than those at SF sites. In addition, the soil wetting rate was high over the SF region, whereas the soil wetting rate was low over the PF region. Aside from air temperature, changes in thawing degree days and solar radiation (Srad) contributed most to soil warming in the PF region, whereas changes in rainfall, Srad and evaporation (EVA) have been identified as the key factors in the SF region. As for soil wetting, changes in snowfall, freezing degree days and vegetation have noticeable nonlinear effects over the PF region, whereas changes in EVA, Srad and rainfall highlighted distinct linear and nonlinear effects in the SF region. These findings enhance our understanding of the hydrothermal impacts of future environmental changes over the QTP.