InSAR Estimates and In-situ Observations of Supra-permafrost Water Storage in Undisturbed and Burned Areas in the Arctic Foothills

The degradation and thawing of permafrost lead to more water stored in the active layer. Understanding this water's storage and flow is important because supra-permafrost groundwater flow is a significant pathway for the lateral export of carbon, which is abundant in permafrost soils.

Because of the density difference between ice and liquid water, seasonal surface deformation occurs as the active layer undergoes a freeze-thaw cycle. In a previous study, we showed that the amount of seasonal surface deformation observed by Interferometric Synthetic Aperture Radar (InSAR) data is proportional to the saturated soil water thickness in the active layer. In this study, we developed an InSAR processing algorithm to extract both seasonal and long-term deformation thaw subsidence signals over undisturbed and burned areas of the tundra. With this processing approach, we analyzed ALOS PALSAR data and studied freeze-thaw deformation within the first three years after the 2007 Anaktuvuk River fire. The seasonal deformation was 0-5 cm in an undisturbed area whereas it was 0-10 cm in a burned area. No long-term surface deformation above the noise level was observed for the undisturbed region, while 0-10 cm/yr of long-term surface subsidence associated with excessive melting with ice-rich permafrost was observed over the burned area. To validate the InSAR deformation results, we conducted field measurements and collected soil core samples at >200 field sites on the North Slope of Alaska in 2018 and 2019. In the summer of 2022, we will be sampling soils over the 2007 Anaktuvuk River Fire following the protocol of our previous work. This study allows us to monitor long-term changes in soil moisture distribution over a large scale and to study the impact of the removal of vegetation and organic matter by wildfires on the freeze-thaw cycles.