The ground thermal regime and permafrost warming at two upland, sloping, and undisturbed sites, Kunlun Mountain, Qinghai-Tibet Plateau

Abstract

Ground temperatures from the surface to 15 m depth were measured for nine years (2008–2016) at two upland and sloping sites, to characterize the ground thermal regime. The two sites were on south and north slopes of Kunlun Mountain, Qinghai-Tibet Plateau, respectively, and were not disturbed by anthropogenic activity. Therefore, changes in ground thermal conditions are indicative of natural variations in permafrost in mountainous terrain. The mean annual air temperatures (Ta) from October 2014–2016 were −4.2 (north slope) and −5.6 °C (south slope), but the corresponding mean annual surface temperatures (Ts) were −2.8 and −1.5 °C. Thawing season n-factors were 1.3 at the north site and 2.1 at the south site, resulting in warmer permafrost on the southern slope, which highlights the significance of air and ground surface temperature in determining the thermal regime of permafrost. The mean annual ground temperature in the active layer (0.5 m depth) at the north site was approximately 0.9 °C lower than at the south site, and the active-layer thickness was ~1.0 m greater on the south slope. The mean annual ground temperature at the top of permafrost (T2.0m) was about 0.6 °C lower at the north site than that at the south site. Rapid warming at the north site during the study period caused the ground temperature at the depth of zero annual amplitude to increase and reach near-parity with the south site. Numerical simulations suggested that permafrost in mountainous regions on QTP will warm by about 0.01 °C/y in the next 50 years.