Thermal Modelling of Post-Fire Permafrost Change under a Warming Coastal Subarctic Climate, Eastern Canada

Forest fires are known to have lasting thermal impacts on permafrost, but there are no previous studies of such effects along the eastern Canadian coastline. One-dimensional thermal modelling was used to examine the ground thermal regime at a coastal forest fire site in the discontinuous permafrost zone near Nain (56.5 degrees N), Nunatsiavut, eastern Canada. Simulations were undertaken for both the unburned forest and adjacent fire-disturbed area, which were modelled to have an initial permafrost thickness of 15.6 m in 1965. Future scenarios incorporated changes to regional air temperature following Representative Concentration Pathway (RCP) 4.5 and 8.5, as well as variations in surface organic material regeneration. Results varied from permafrost thinning but persisting beyond 2099 under RCP4.5 (unburned) to thawing entirely by 2060 under RCP8.5 (high severity burn, no organic material regeneration). In all burned scenarios, a supra-permafrost talik developed immediately following disturbance, but in most cases, frozen ground re-aggraded after several decades. Our findings are broadly consistent with those from western North America and demonstrate that the main impact of fire is to accelerate permafrost thaw due to climate warming.