Monitoring and modeling the influence of snow pack and organic soil on a permafrost active layer, Qinghai–Tibetan Plateau of China

Abstract As a result of global warming, the depth of the permafrost active layer on the Qinghai–Tibet Plateau (QTP) has been increasing progressively during the past few decades. The Cold and Arid Regions Environmental and Engineering Research Institute, Chinese Academy of Sciences, established the Binggou and Tanggula research stations on the QTP to monitor the impacts of snow pack and tundra soil on the permafrost active layer. In order to reproduce active layer dynamics in the present climate, the CoupModel, which calculates vertical heat and water processes in a soil–snow–atmosphere system, was successfully adjusted and applied for the two research stations. Subsequently, the calibrated model was used to provide an evaluation of the potential response of the active layer to different scenarios of climate warming and precipitation increase at Binggou station. The results reveal: ① the soil freezes deeper for snow depths less than 20 cm in the present climate, compared to the situation without snow cover. Increased albedo, due to shallow snow cover, reduces the absorption of solar irradiation and decreases soil temperature. However, this positive effect is lost with increasing precipitation and snow depth in winter. The decrease of simulated cumulative ground heat flux in winter along with thicker snow depth indicates that the thicker snow pack gradually insulates the subsoil against energy losses to the atmosphere in winter, which induces a reduction of active layer frozen depth. ② The model predicted an increase of maximum active layer thawing depth from today 150 cm to about 350 cm as a result of a 4 °C warming and a talik formation at the top of the permafrost as a result of a 6 °C warming. The other investigation concerns the influence of organic soil layer depth on the active layer at Tanggula station. The model results reveal that the maximum thawing depth of the active layer in summer gradually decreases along with the increase of the soil organic layer depth. The maximum thawing depth is close to 300 cm when ignoring the organic layer, while it is about 150 cm with a realistic organic layer of 40 cm depth. The results reveal that the organic layer provides a protection against active layer deepening in summer. Therefore, both the roles of snow and organic soil are of importance for the behavior of permafrost under climate warming conditions.

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