Modelling the significance of snow-vegetation interactions for active layer dynamics in an Arctic permafrost region subjected to tundra shrubification

Permafrost is warming globally and the extent of this warming is locally variable in space and time due to an array of factors. In the Arctic, vegetation is one of these factors, whichever influenced by climate change is undergoing a transformation through an increase in height and extent of shrubs on the tundra. In turn, changes in vegetation also alter the thermal properties of the snow cover in winter due to processes like snow trapping; potentially further warming permafrost. However, permafrost models have been limited in the combined representation of small-scale spatial variability of snow and vegetation. By combining the CryoGrid permafrost model with observed characteristics of local snow cover, vegetation, and soil stratigraphies, the present work investigates the spatial heterogeneity of permafrost active layer dynamics in Siksik Creek, NW Canada. The modelling efforts indicate that vegetation-induced increased insulation capacity of snow cover in winter, has the potential to directly influence the maximum active layer thickness in autumn, albeit to a limited extent. Two main factors, soil moisture content and soil stratigraphy, were found to strongly mediate the strength of this inter-seasonal feedback, which under certain conditions is voided or even reversed. As such, taller shrubs are potentially a stabilizing factor for active layer development due to the insulating effect of drier top soils as a result of higher evapotranspiration rates. Finally, most of the observed active layer thickness variability in Siksik Creek could be explained due to the combined effects of soil stratigraphies and soil moisture contents