Impact of lateral groundwater flow on hydrothermal conditions of the active layer in a high arctic hillslope setting

• Main Authors: Hamm, Alexandra, Frampton, Andrew
• Format: Text
• Language: English
• Published: 2021
• Subjects: Adventdalen; Arctic; Svalbard; Climate change; permafrost
• Online Access: https://doi.org/10.5194/tc-2021-60; https://tc.copernicus.org/preprints/tc-2021-60/

Modeling the physical state of permafrost landscapes is a crucial addition to field observations in order to understand its feedback mechanisms within a warming climate. A common hypothesis in permafrost modeling is that vertical heat conduction is most relevant to derive subsurface temperatures. While this approach is mostly applicable to flat landscapes with little topography, landscapes with more topography are subject to lateral flow process as well. With our study, we want to contribute to the growing body of evidence that lateral surface- and subsurface processes can have a significant impact on permafrost temperatures and active layer properties. We use a numerical model to simulated two idealized hillslopes with inclinations that can be found in Adventdalen, Svalbard, and compare them to a flat control case. We find that ground temperatures within the active layer uphill are generally warmer than downhill in both slopes (up to ~1.2 °C in the steep, and ~0.7 °C in the medium slope). Further, the slopes are found to be warmer in the uphill section and colder in the very bottom of the slopes compared to the flat control case. As a result, maximum thaw depth increases by about 5 cm from the flat (75 cm) to the steep slope (80 cm), while the medium case does not exhibit a deepening in thaw depth (75 cm). Uphill warming on the slopes is explained by additional energy gain through infiltration and lower evaporation rates due to a overall drier environment. The major governing process causing the cooling on the downslope side is heat loss to the atmosphere through evaporation in summer and enhanced heat loss in winter due to wetter conditions and resulting higher thermal conductivity. On a catchment scale, these results suggest that temperature distributions in hilly terrain can vary considerably compared to flat terrain, which might change the response of subsurface hydrothermal conditions to ongoing climate change.