Abstract
The Qinghai-Tibet Plateau (QTP) has the largest extent of high altitude permafrost at the middle and low latitudes in northern hemisphere and is surrounded by dozens of seasonally frozen ground. Rising air temperatures have resulted in frozen ground degradation over QTP since the last century. Based on the daily frozen soil depth, annual mean daily minimum air temperatures and annual mean air temperatures obtained from 19in-situobservations over QTP, the changes in the thickness, temporal and spatial distributions of frozen ground, as well as the associated attributions, are analyzed for the period of 1960-2019. The results show that the maximum depth of frost penetration, the beginning time of soil freezing and the ending time of soil thawing have changed considerably. On average, the maximum depth of frost penetration (MDFP) has reduced by 0.14 similar to 1.71 m at most stations. The annual frozen period has decreased by about 40 days. The changes in seasonal freezing of soils appear to be attributed to the rising of minimum air temperatures in winter, especially at the higher elevations range from 4500 to 5000 m.
Highlights
Frozen ground is one of the consequences of the alternation between cold and warm climate status, it is very sensitive to climate change
The observation suggested that the beginning date of soil freezing becomes later, and the beginning date of soil thawing becomes earlier (Gao et al, 2008), which all confirmed that frozen ground over the Qinghai-Tibet Plateau (QTP) degraded gradually
During 1960–2019, the averaged MDFP decreased by 1.37 m above 4500 m, while decreased by 0.35 m below 4500 m. These results suggest that the variations of maximum depth of frost penetration are correlated to the higher elevations
Summary
Frozen ground is one of the consequences of the alternation between cold and warm climate status, it is very sensitive to climate change. Since 1967, seasonally frozen depth (SFD) has thinned by 5 cm, with an average rate of 0.7 cm/year over the eastern QTP (Zhao et al, 2004), and the maximum depth of frost penetration (MDFP) shows a decreasing trend over the QTP since 1980s (Wang et al, 2001), and decreases by up to 33 cm since the middle of 1980s (Li et al, 2009). The observation suggested that the beginning date of soil freezing becomes later, and the beginning date of soil thawing becomes earlier (Gao et al, 2008), which all confirmed that frozen ground over the QTP degraded gradually
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