Permafrost Thermal Conditions are Sensitive to Shifts in Snow Timing
Changes in snow precipitation can significantly affect permafrost thermal conditions and thaw depth, potentially exposing more carbon-laden soil to microbial decomposition. A fully coupled process-based surface/subsurface thermal hydrology model with surface energy balance is used by NGEE Arctic scientists to analyze the impact of intra-annual variability in snow on permafrost thermal regime and the active layer thickness. In the four numerical scenarios considered, Ahmad Jan (ORNL) and his colleagues systematically altered simulations to change timing of snowfall, while keeping all other forcing parameters constant. The scenarios represent subtle shifts in snow timing, but the snow onset/melt days, the end of winter snowpack depth, and the total annual snow precipitation were the same in all scenarios. The simulations reveal that small shifts in the timing of snow accumulation can have significant effects on subsurface thermal conditions leading to active layer deepening and even talik formation when snowfall arrives earlier in the winter. The shifts in snow timing have a stronger impact on wetter regions, especially soil underneath small ponds, as compared to drained (upland) regions. These findings suggest that reliable projections of air temperature and total snowfall may not be sufficient to understand permafrost degradation and associated thermal and hydrological changes.