Thermal regime of warm-dry permafrost in relation to ground surface temperature in the Source Areas of the Yangtze and Yellow rivers on the Qinghai-Tibet Plateau, SW China

摘要

AbstractEcology, hydrology, and natural resources in the source areas of the Yangtze and Yellow rivers (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 annualTa(MAAT) and mean annualGST(MAGST) were regionally averaged at −3.19±0.71°C and −0.40±1.26°C. There is a close relationship betweenGSTandTa(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 ofGST, thermal offset, and temperature gradient in the shallow permafrost.Graphical abstractDisplay OmittedHighlights•Close relationship exists between ground surface and air temperatures in the SAYYR.•Relatively consistent surface offset due to dwarf vegetation or barren ground surface.•Small thermal offset as comparable frozen and thawed thermal conductivity of soil.•Surface characteristics lead to heterogeneity of active layer thickness in the SAYYR.•Warm-dry permafrost temperature may be linked to ground surface temperature.