The role of water tracks in permafrost hillslope hydrology

Hillslope hydrology in upland permafrost regions (e.g., Alaska, High Canadian Arctic, Russia, Antarctica) is often dominated by water tracks, zones of enhanced soil moisture in unchannelized depressions that concentrate water flow downslope. Continued warming of permafrost regions may alter hydrologic cycling, leading to increased frequency of extreme hydrologic events like drought and flooding and modification to biogeochemical cycles. It is therefore imperative to parametrize the role of water tracks in the hydrology of the permafrost environments. In this study, we synthesize uniting and distinguishing hydrologic characteristics of water tracks across permafrost regions and then examine water track seasonality, occurrence, and contribution to the permafrost hydrologic cycle using field observation, remote sensing, and numerical modeling for permafrost hillslopes on the North Slope of Alaska, USA. Results suggest that water tracks occur across climate and hydrologically disparate permafrost landscapes but have ubiquitous surface wetness, vegetation, and snow duration patterns that can be identified remotely using 3-m resolution PlanetScope imagery. Detailed field investigation from 2022-2024 of three study sites with ~20 water tracks and ~15 gullies suggests that water tracks are hydrologically distinct from larger, variably channelized hillslope features and require more precipitation and time to initiate discharge following rainfall events. Across these study sites, concentration-discharge relationships reveal that water tracks can exhibit drastically different dynamics of particulate and dissolved organic carbon export based on landscape attributes. Young water fraction analysis found that in 2023, 24–78% of runoff from the study sites was young water less than 35 days old during the observed summer thaw season, and model-estimated young water fraction increased by two-fold when factoring in the fall shoulder season. Geophysical investigations indicate the presence of buried ice wedges on the margins of studied water tracks, supporting the idea that water tracks may form from the coalesced drainage of patterned ground. Over time, these drainage patterns likely evolve and widen into present-day water tracks that act as flow conduits and discharge liquid water into the fall shoulder season after the adjacent hillslope has frozen. Our ongoing analysis explores how water track flow seasonality may influence observed ground collapse and mediate or enhance the permafrost-carbon feedback.