Groundwater controls on post-fire permafrost thaw: Water and energy balance effects

• Main Authors: Zipper, Samuel, Lamontagne-Halle, Pierrick, McKenzie, Jeffrey, Rocha, Adrian
• Format: Report
• Language: unknown
• Published: EarthArXiv 2018
• Subjects: Physical Sciences and Mathematics; Environmental Sciences; Earth Sciences; Hydrology; Active layer thickness; permafrost; Alaska
• Online Access: https://dx.doi.org/10.17605/osf.io/27s3z; https://eartharxiv.org/27s3z/

Fire frequency and severity are increasing in high latitude regions, but the degree to which groundwater flow impacts the response of permafrost to fire remains poorly understood and understudied. Here, we use the Anaktuvuk River Fire (Alaska, USA) as an example to simulate groundwater-permafrost interactions following fire. We identify key thermal and hydrologic parameters controlling permafrost and active layer response to fire both with and without groundwater flow, and separate the relative influence of changes to the water and energy balances. Our results show that mineral soil porosity, which influences the bulk subsurface thermal conductivity, is a key parameter controlling active layer response to fire in both the absence and presence of groundwater flow. However, neglecting groundwater flow increases the perceived importance of subsurface thermal properties, such as the thermal conductivity of soil solids, and decreases the perceived importance of hydrologic properties, such as the soil permeability. Furthermore, we demonstrate that changes to the energy balance (increased soil temperature) are the key driver of increased active layer thickness following fire, while changes to the water balance (decreased groundwater recharge) lead to reduced landscape-scale variability in active layer thickness and groundwater discharge to surface water features. These results indicate that explicit consideration of groundwater flow is critical to understanding how permafrost environments respond to fire.