Two-dimensional simulation of island permafrost degradation in Northeastern Tibetan Plateau

Abstract

Despite the response of ground temperatures to increases in air temperature, discontinuous and isolated bodies of permafrost are strongly affected by lateral heat fluxes from adjacent unfrozen zones. However, many current simulations consider heat flow in only one-dimension (1D) and thus cannot represent two or three-dimensional effects. To address this issue, we use fine-scale in situ measurements and two-dimension (2D) heat conduction simulations and compare the simulated ground thermal evolution and degradation of island permafrost to a 1D simulation. The 2D simulation reasonably represented seasonal and interannual features of the ground thermal regime, such as temperature profile, thawing/frozen depth, and permafrost body width. Lateral thawing of the island permafrost was dominant, and was about one order of magnitude greater than the modelled vertical thaw. In the vertical direction, downward permafrost thaw caused by increase in air temperature rise was restricted by phase change of ground ice near the permafrost table during the simulation period, contributing little to the overall permafrost degradation. Rates of permafrost degradation in the 1D simulation were 1.6–1.8 times lower than the simulation considering lateral heat fluxes. The field monitoring and numerical simulation highlight the importance of coupling lateral heat transfer in permafrost models.