Water Tracks Enhance Water Flow Above Permafrost in Upland Arctic Alaska Hillslopes. Issue 2 (18th February 2020)

• Record Type: Journal Article
• Authors: Evans, Sarah G.; Godsey, Sarah E.; Rushlow, Caitlin R.; Voss, Clifford
• Is Part Of: Journal of geophysical research. Volume 125:Issue 2(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-02-18
• Subjects: permafrost -- water tracks -- hydrologic cycling -- coupled modeling; Geomorphology -- Periodicals; 551.3
• DOI: 10.1029/2019JF005256
• Languages: English
• ISSNs: 2169-9003

Abstract

Abstract: 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. Plain Language Summary: The flow of liquid water in the Arctic is largely constrained to the ground surface and shallow subsurface above perennially frozen ground known as permafrost. As the Arctic climate warms, permafrost will thaw more deeply, altering the paths along which water is transported from mountains to downstream areas that discharge water into the ocean. One of the primary paths that water flows in the Arctic is along water tracks, curvilinear features on hillslopes that fill with and route water in response to snowmelt and rainfall when the soil above permafrost thaws in the summer. Although hillslopes with water tracks cover as much as one third of the Arctic landscape, little is known about the magnitude and seasonality of flow through water tracks. In this study, we create a three‐dimensional subsurface model of an Arctic hillslope with a water track that incorporates field measurements from the North Slope of Alaska, USA. Results indicate that subsurface water flows preferentially from adjacent hillslopes into water tracks, especially after large rainstorms and in the autumn when the adjacent hillslopes start to freeze. These results suggest that water tracks may play an important, but complex, role in predicting water budget responses to changing Arctic landscapes. Key Points: A 3‐D subsurface flow model with freeze‐thaw heat transport is used to examine the role of water tracks on the Arctic hydrologic cycle Water tracks are more likely than the adjacent hillslopes to route recharge from large storms and serve as late‐season flow conduits Differentiating water track conditions from hillslopes affects subsurface water storage but has a limited effect on discharge magnitudes