Characteristic, changes and impacts of permafrost on Qinghai-Tibet Plateau

Qinghai-Tibet Plateau (QTP) is the largest high-altitude permafrost zone in the mid-latitudes. Due to the climate warming, permafrost degradation on the QTP has been widely recorded in the past decades. Since it greatly affects the East Asian monsoon, and even the global climate system, it is extremely important to understand permafrost current state, changes and its impacts. Based on literature reviews and some new data, this paper summarizes the characteristics of the current state permafrost on the QTP, including the active layer thickness (ALT), the spatial distribution of permafrost, permafrost temperature and thickness, as well as the ground ice and soil carbon storage in permafrost region. The new results showed that the permafrost and seasonally frozen ground area (excluding glaciers and lakes) is 1.06 million square kilometers and 1.45 million square kilometers on the QTP. The sub-stable, transitional, and unstable permafrost accounts for 30.4%, 22.1% and 22.6% of the total permafrost area. The permafrost thickness varies greatly among topography, with the maximum value in mountainous areas, which could be deeper than 200 m, while the minimum value in the flat areas and mountain valleys, which could be less than 60 m. The mean active layer thickness of the permafrost on the QTP is 2.3 m, with 80% of the permafrost regions ranges from 0.8 m to 3.5 m. During 1980 to 2015, soil temperature at 0−10, 10−40, 40−100, 100−200 cm increased at a rate of 0.439, 0.449, 0.396, and 0.259°C/ 10 a, respectively. From 2004 to 2018, the increasing rate of the soil temperature at the bottom of active layer was 0.486°C/ 10 a. These results show that the permafrost degradation has been accelerating. The permafrost degradation largely reduces the soil moisture. The ground ice volume of the permafrost is estimated up to 1.27×104 km3 (liquid water equivalent). The soil organic carbon in the upper 2 m of permafrost region is about 17 Pg; there is a large uncertainty in this estimation however due to the great heterogeneities in the soil column. Although the permafrost ecosystem is a carbon sink at the present, it is possible that it will shift to a carbon source due to the loss of soil organic carbon along with permafrost degradation. Overall, this paper shows that the plateau permafrost has undergone remarkable degradation during past decades, which are clearly proven by the increasing ALTs and ground temperature. Most of the permafrost on the QTP belongs to the unstable permafrost, meaning that permafrost over TPQ is very sensitive to climate warming. The permafrost interacts closely with water, soil, greenhouse gases emission and biosphere. Therefore, the permafrost degradation greatly affects the regional hydrology, ecology and even the global climate system. This paper also proposes approaches and methods to study the interactive mechanisms between permafrost and climate change, and the results can serve as a scientific basis for environmental protection, engineering design and construction in cold regions.