Degradation of warm permafrost and talik formation on the Qinghai‒Tibet Plateau in 2006‒2021

Permafrost is degrading globally, particularly those with low thermal stability on the Qinghai‒Tibet Plateau, owing to climate change. However, the inadequacy of direct research on permafrost degradation based on in-situ monitoring limits the prediction of permafrost degradation and engineering practices. This study explored the processes and modes of permafrost degradation into talik by analyzing ground temperature data from five points in the hinterland of the Qinghai‒Tibet Plateau from 2006 to 2021. The results showed that the degradation of the warm permafrost layer with a geothermal gradient of zero occurred simultaneously in the top and bottom directions. The rate of permafrost degradation from the top down and bottom up increase during the degradation process, but the increase of the former is more drastic after the formation of thawed interlayer. Additionally, the construction of the Qinghai‒Tibet Railway changed the degradation modes of the permafrost in adjacent natural sites through horizontal heat transfer, particularly after through talik formation under the embankment. The findings suggest that taking countermeasures before or immediately after forming thawed interlayer is more effective. When evaluating the thermal impact of projects in warm permafrost regions, special attention should be given to the horizontal heat transfer process that may result from the formation of a through talik.