CONTRASTING HYDROGEOLOGIC RESPONSES TO CLIMATE WARMING IN PERMAFROST AND SEASONALLY FROZEN GROUND

Permafrost and seasonally frozen ground underlay approximately half of the Northern Hemisphere exposed land surface. Climate warming is expected to reduce the areal extent of both permafrost and seasonally frozen ground, altering groundwater discharge to streams. While the effects of permafrost degradation on groundwater discharge have been analyzed, quantification of how groundwater discharge in degrading permafrost differs from that in seasonally frozen ground is lacking. This study simulates coupled groundwater flow and heat transport under freeze-thaw conditions for hillslopes underlain by permafrost and seasonally frozen ground and compares groundwater discharge outputs under both non-warming and IPCC-projected warming scenarios over decadal scales.

Model results demonstrate that, without warming, seasonally frozen ground hillslopes generally transmit more groundwater flow and have higher magnitudes of groundwater discharge than hillslopes with permafrost. For the parameter scenario considered in this modeling study, there is a maximum of 87% more groundwater discharge in catchments with seasonally frozen ground than with permafrost. With IPCC-projected warming trends, over the coming decades there will be increased groundwater discharge for regions with both permafrost and seasonally frozen ground. Permafrost hillslopes will likely experience an order of magnitude greater relative change in groundwater discharge than hillslopes underlain by seasonally frozen ground despite transmitting a smaller volume of groundwater. In this study, groundwater discharge increased up to 190% in seasonally frozen ground versus up to 1340% in permafrost. These findings indicate that water resource planning in cold regions should prioritize research in permafrost terrains rather than regions with seasonally frozen ground, as areas with permafrost will likely see the largest changes in groundwater contribution to streamflow and consequently, aquatic ecosystems.