Water tracks enhance water flow above permafrost in upland Arctic Alaska hillslopes

Upland permafrost regions occupy approximately one third of the Arctic landscape. In upland regions, hydrologic fluxes are influenced by water tracks, curvilinear features on hillslopes that preferentially fill with and route water in response to snowmelt and rainfall when the soil above continuous permafrost thaws in the summer. As continued warming of the Arctic may alter hydrologic cycling leading to increased frequency of extreme hydrologic events like drought and flooding as well as modification of biogeochemical cycling, it is imperative to untangle the interplay between precipitation, runoff, and subsurface flow as water is routed from upland Arctic regions to the Arctic Ocean. This study quantifies how ground surface temperatures affect groundwater discharge from hillslopes with water tracks in the upland Arctic by employing a three-dimensional, physically based subsurface flow model with variable saturation and freeze and thaw capabilities that is calibrated to field measurements from the Upper Kuparuk River watershed on the North Slope of Alaska, USA. Model analysis indicates that higher ground surface temperatures along water track hillslopes promote increases in groundwater discharge where water tracks act as conduits for large recharge events and continue to discharge groundwater into the autumn after the adjacent hillslope has frozen. Simulating the conditions that distinguish water tracks from their hillslope watersheds changes subsurface water storage and ground thermal responses but does not alter the total magnitude of groundwater discharge outside of parameter uncertainty. These findings suggest that water tracks play a complex and critical role in hydrologic cycles of the upland Arctic.