The impact of fires on permafrost: A case study of the Shestakovka River basin in Siberia using a one-dimensional mathematical model

Permafrost regions are vulnerable to forest fires that are increasing under global warming. This study presents the results of field experiments and mathematical modeling of short-term (one hour) forest fires. The experimental site Levaya Shestakovka (Central Yakutia, Russia) has been used as example. Three fire experiments were conducted using logs of Siberian larch and Scots pine which serve as a basis for the mathematical model. The model is based on solving the one-dimensional Stefan problem with unsaturated soil filtration and accounting for snow cover. The lower boundary condition is the geothermal heat flux, while the upper boundary condition is the heat exchange with the atmosphere. The field experiments show that only 8 percent of the heat from the fire has penetrated into the soil, which is supported by our model that indicates no significant effect on heat and mass transfer processes from short-term forest fires into permafrost. The research indicates that the contribution of short–lived forest fires to ground temperature changes is negligible; the heatwave penetrated only 0.5 m into the ground. Modeling showed that short-term forest fires have no significant effect on heat and mass transfer processes in permafrost. Thus, the research results indicate that low-severity forest fire regimes are not significant for permafrost thawing processes.