Changes in active layer thickness over the Qinghai‐Tibetan Plateau from 1995 to 2007

Abstract

[1] The active layer over permafrost plays a significant role in surface energy balance, hydrologic cycle, carbon fluxes, ecosystem, and landscape processes and on the human infrastructure in cold regions. Over a period from 1995 to 2007, a systematic soil temperature measurement network of 10 sites was established along the Qinghai-Tibetan Highway. Soil temperatures up to 12 m depth were continuously measured semimonthly. In this study, we investigate spatial variations of active layer thickness (ALT) and its change over the period of record. We found that ALT can be estimated with confidence using semimonthly soil temperature profiles compared to those determined from available daily soil temperature profiles over the Qinghai-Tibetan Plateau. The primary results demonstrate that longterm and spatially averaged ALT is ∼2.41 m with a range of 1.32-4.57 m along the Qinghai-Tibetan Highway. All monitoring sites show an increase in ALT over the period of their records. The mean increasing rate of ALT is ∼7.5 cm/yr. ALT shows a closely positive correlation with the thawing index of air temperature on the plateau. We estimated ALT using the thawing index over a period from 1956 to 2005 near the Wudaoliang Meteorological Station in the northern plateau. ALT had no or very limited change from 1956 to 1983 and a sharp increase of ∼39 cm from 1983 to 2005. The magnitude of ALT increase is greater in the warm permafrost region than in the cold permafrost region. The primary control of increase in ALT is caused by an increase in summer air temperature, whereas changes in the winter air temperature and snow cover condition play no or a very limited role.

Temporal and spatial variations of the active layer along the Qinghai-Tibet Highway in a permafrost region

“…In the past 13 years, the ALT increased by 46 cm, with a variation rate of 3.6 cm a -1 . This value is smaller than that observed by Wu et al [22] (7.5 cm a -1 ). The main reason for this difference lies in the fact that the observation sites selected by Wu et al [22] were mostly set up for dynamic monitoring of the Qinghai-Tibet Highway/Railway embankment in permafrost.…”

“…This value is smaller than that observed by Wu et al [22] (7.5 cm a -1 ). The main reason for this difference lies in the fact that the observation sites selected by Wu et al [22] were mostly set up for dynamic monitoring of the Qinghai-Tibet Highway/Railway embankment in permafrost. Therefore most of them are located within the range of tens of meters on both sides of the highway/railway, where road engineering and human activity disturbance is more frequent, and thus the increase in ALT is larger.…”

“…Studies of the active layer and permafrost on the QTP have received much recent attention [16][17][18][19][20]. Recent work in the area has shown that, due to global climate warming, the permafrost on the QTP has degraded remarkably, including a rise in permafrost temperature, an increase in the thickness of the active layer, and a decrease in permafrost area [21][22][23][24]. This degradation of permafrost may alter the groundwater table, resulting in more arid soil, and exacerbating desertification [21,25,26].…”

Longitudinal patterns of periphyton biomass in Qinghai–Tibetan Plateau streams: An indicator of pasture degradation?

“…Especially in the "Three-River Headwaters" region, moderate or seriously degraded pasture area accounted to 12 million hm 2 , accounting for 58% of the available pasture area (Liu et al, 2008). In recent decades, permafrost on QinghaieTibetan Plateau has also degraded seriously (Wu and Zhang, 2010), and will decrease by approximately 81% by the end of the 21st century (Liu et al, 2011;Guo et al, 2012). The main driving forces of these degenerations are climate change, strong human activity (overgrazing) and devastation due to rodents (Ma et al, 1999;Liu et al, 2008;Yan et al, 2011).…”

Modeling permafrost thaw and ecosystem carbon cycle under annual and seasonal warming at an Arctic tundra site in Alaska

“…Climate warming has deepened the ALT by ∼7.5 cm/yr in the Tibetan region [Wu and Zhang, 2010] and is projected to increase ALT more than 30% during this century across tundra area in the Northern Hemisphere [Anisimov et al, 1997[Anisimov et al, , 2002Dankers et al, 2011]. On the other hand, growing season gross primary productivity (GPP) and net ecosystem exchange (NEE, i.e., GPP+ R eco ) may also increase as permafrost is degraded, in spite of less change in annual or growing season ecosystem respiration (R eco , negative value) Trucco et al, 2012].…”