thermal regime of warm-dry permafrost on the Qinghai-Tibet Plateau

What is it about?

Ecology, hydrology, and natural resources in the source areas of the Yangtze and Yellowrivers (SAYYR) are closely linked to interactions between climate and permafrost. However, a comprehensive study of the interactions is currently hampered by sparsely- and unevenly-distributed monitoring sites and limited field investigations. In this study, the thermal regime of warm-dry permafrost in the SAYYR was systematically analyzed based on extensive data collected during 2010–2016 of air temperature (Ta), ground surface temperature (GST) and ground temperature across a range of areas with contrasting land-surface characteristics. Mean annual Ta (MAAT) and mean annual GST (MAGST) were regionally averaged at −3.19 ± 0.71 °C and −0.40± 1.26 °C. There is a close relationship between GST and Ta (R2=0.8477) as obtained by a linear regression analysis with all available daily averages. The mean annual temperature at the bottom of the active layer (TTOP) was regionally averaged at −0.72 ± 1.01 °C and mostly in the range of −1.0°C and 0 °C except at Chalaping (~−2.0 °C). Surface offset (MAGST–MAAT) was regionally averaged at 2.54 ± 0.71 °C. Thermal offset (TTOP-MAGST) was regionally averaged at −0.17± 0.84 °C, which was generally within−0.5 °C and 0.5 °C. Relatively consistent thermal conductivity between the thawed and frozen states of the soils may be responsible for the small thermal offset. Active layer thickness was generally smaller at Chalaping than that on other parts of the QTP, presumably due to smaller climatic continentality index and the thermal dampening of surface temperature variability under the presence of dense vegetation and thick peaty substrates.We conclude that the accurate mapping of permafrost on the rugged elevational QTP could be potentially obtained by correlating the parameters of GST, thermal offset, and temperature gradient in the shallow permafrost.

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Why is it important?

As the water tower of Asia, the source areas of the Yangtze and Yellow rivers (SAYYR) play decisive roles in the world. It responds significantly to climate changes and anthropocentric activities. Previous studies demonstrate more than half of the area of the SAYYR is occupied by permafrost, which is actually warm (>-1°C) and dry (with little ground ice). This study comprehensively studied the correlations between permafrost and climate, particularly the ground surface temperature through complex interactions of surface characteristics. It will facilitate relevant studies of ecology, environment and resources.

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