Climate change impacts on supra-permafrost soil and aquifer hydrology: broader, deeper, and longer activity

Abstract: The thermal dynamics and hydrology of active layer soils and supra-permafrost aquifers determine the fate of the vast pool of carbon that they hold. In permafrost watersheds of Arctic Alaska, air temperature has warmed by up to 3.5 °C and snowfall has increased by up to ~40 mm from 1981 to 2020. How these changes impact the seasonal to decadal hydrological activity of the carbon-rich aquifers is mostly unknown. Observation-informed thermal hydrology modeling of a hillslope drained by a headwater stream (Imnavait Creek) within continuous permafrost showed profound changes from 1981 to 2020. Warmer summer temperatures deepened annual thaw depths. Steadily warming winter air temperatures, heavier snowfall, and stored energy from summer increased annual water outflow from the hillslope aquifer to the stream, warmed soil temperatures, and expanded and prolonged zero-curtain (stable at 0 °C) zones. In 2017-2018, zero-curtain areas with liquid water persisted through winter. Our findings reveal that both summer and winter warming drive year-round aquifer dynamics, creating conditions that amplify the permafrost-carbon-climate feedback.