Dynamics and characteristics of soil temperature and moisture of active layer in the central Tibetan Plateau

Abstract

Hydro-thermal characteristics of the active layer are critical during freezing-thawing cycles, causing the moisture and heat exchanges between both permafrost and atmosphere in permafrost regions. There is better understanding of these characteristics in high-latitude permafrost areas, while comparatively little is known in the middle-low latitude areas. Here, we used field monitoring data along with statistical models to quantitatively analyze the hydro-thermal dynamics of the freezing-thawing processes at the Tanggula (TGL) site in permafrost regions of Qinghai-Tibetan Plateau (QTP). This combined approach was used to examine the hydro-thermal characteristics in high-altitude permafrost regions. Our results revealed that the duration of the freezing process was much shorter than that of the thawing process. During freezing-thawing processes, the amplitude variation in soil temperature had a significant logarithmic relationship with depth. There was a significant exponential relationship between soil water content at a depth of 5 cm and monthly precipitation. The averaged energy in the active layer consumed for phase change from water to ice was 145.53 MJ/m2. Finally, we analyzed the quantitative hydro-thermal characteristics and influential factors during the freezing and thawing processes; the different hydro-thermal processes occurring in high-altitude permafrost regions were compared with those in high latitude permafrost regions. Collectively, these results offer a perspective on the difference in permafrost across different region and also provide a reference for the parameterization of land surface models.