9:30 AM - 9:45 AM
[ACG42-03] Post-wildfire Surface Deformation in Canadian Northwest Territories Revealed by Sentinel-1 InSAR
Keywords:Wildfire, Permafrost, Deformation, InSAR, Sentinel-1
Permafrost thaw has received increasing attention these days due to its high sensitivity to climate change and complex feedback to ecological, hydrological, and biological processes. Meanwhile, an increasing number of wildfires has been reported over the Arctic tundra and boreal forests where permafrost usually underlies. Wildfires in these regions could turn boreal forests from carbon sinks into carbon emitters (at least) during the fire. In addition, depending on the ice extent, wildfires could initiate an abrupt thaw of permafrost that could last much longer than the period of burning and potentially release the frozen carbon again into the atmosphere. However, the details of the post-fire abrupt thaw remain uncertain.
The Northwest Territories, Canada is largely underlain by continuous permafrost. The increasingly prevalent wildfires over the Northwest Territories could greatly alter the underlying permafrost dynamics through dramatic changes in near-surface vegetation and groundwater hydrology and lead to irreversible ground deformation. Such deformation would alter the landform and local hydrology and could be responsible for further carbon emissions to the atmosphere. Therefore, it is worth studying the wildfire-induced deformation in permafrost regions to better understand the intricate interplay between wildfire, permafrost dynamics, and the land surface system. At present, wildfires have increased dramatically in the high-latitude areas in the Northwest Territories, but how they affect permafrost landforms and the extent of deformation there are still unknown. Therefore, the first and foremost work is to investigate the magnitude of these deformations and then look into possible influential factors.
In permafrost areas, in situ deformation measurement data are always hard to acquire due to the harsh environment and poor accessibility, especially in the winter season. The satellite-based interferometric Synthetic Aperture Radar (InSAR) technology, which is widely applied in observing ground deformation all over the world, provides a powerful tool to help us measure post-wildfire deformation in permafrost regions.
In this study, by performing the time-series analysis on Sentinal-1 InSAR data, we investigate the post-wildfire deformation responses in a fire scar located beside the downstream McKenzie River, Northwest Territories, Canada. This area is underlain by continuous permafrost. From July 23rd to August 2nd 2019, the wildfire occurred and left a fire scar of about 584 km2. From InSAR-derived displacement data, we investigate the temporal and spatial patterns of ground deformation, including the span-fire and post-fire signals from July 2019 to July 2021.
The results show that wildfires would cause obvious permafrost degradation which could be manifested as greater subsidence signals (up to 10cm) in most of the burned area than in the unburned area two years after the wildfire. Due to the reduction of the vegetation cover and organic layers and the higher albedo of the fire scar, more heat would be absorbed by the permafrost layers under burned areas during the thawing season, leading to more ground ice thawing that can form greater subsidences (Fig. 1c, g). Besides subsidence, in the lower land within and near the burned area, a slightly greater uplift signal than in other areas could be found during the early freezing season(Fig. 1a, e). This could be due to the increased soil moisture in these areas. After the thawing season, more ground ice would melt in burned areas, and the melting water would drain to lower lands, concentrate and then freeze in the upper soil layers. However, when the freezing front reached deeper layers in the later freezing season, such uplift patterns related to elevations faded away.
The study encompasses wildfire-caused ground deformation in permafrost environments, through which, we aim to contribute to a more detailed understanding of the relationships between wildfire impacts and permafrost dynamics.
The Northwest Territories, Canada is largely underlain by continuous permafrost. The increasingly prevalent wildfires over the Northwest Territories could greatly alter the underlying permafrost dynamics through dramatic changes in near-surface vegetation and groundwater hydrology and lead to irreversible ground deformation. Such deformation would alter the landform and local hydrology and could be responsible for further carbon emissions to the atmosphere. Therefore, it is worth studying the wildfire-induced deformation in permafrost regions to better understand the intricate interplay between wildfire, permafrost dynamics, and the land surface system. At present, wildfires have increased dramatically in the high-latitude areas in the Northwest Territories, but how they affect permafrost landforms and the extent of deformation there are still unknown. Therefore, the first and foremost work is to investigate the magnitude of these deformations and then look into possible influential factors.
In permafrost areas, in situ deformation measurement data are always hard to acquire due to the harsh environment and poor accessibility, especially in the winter season. The satellite-based interferometric Synthetic Aperture Radar (InSAR) technology, which is widely applied in observing ground deformation all over the world, provides a powerful tool to help us measure post-wildfire deformation in permafrost regions.
In this study, by performing the time-series analysis on Sentinal-1 InSAR data, we investigate the post-wildfire deformation responses in a fire scar located beside the downstream McKenzie River, Northwest Territories, Canada. This area is underlain by continuous permafrost. From July 23rd to August 2nd 2019, the wildfire occurred and left a fire scar of about 584 km2. From InSAR-derived displacement data, we investigate the temporal and spatial patterns of ground deformation, including the span-fire and post-fire signals from July 2019 to July 2021.
The results show that wildfires would cause obvious permafrost degradation which could be manifested as greater subsidence signals (up to 10cm) in most of the burned area than in the unburned area two years after the wildfire. Due to the reduction of the vegetation cover and organic layers and the higher albedo of the fire scar, more heat would be absorbed by the permafrost layers under burned areas during the thawing season, leading to more ground ice thawing that can form greater subsidences (Fig. 1c, g). Besides subsidence, in the lower land within and near the burned area, a slightly greater uplift signal than in other areas could be found during the early freezing season(Fig. 1a, e). This could be due to the increased soil moisture in these areas. After the thawing season, more ground ice would melt in burned areas, and the melting water would drain to lower lands, concentrate and then freeze in the upper soil layers. However, when the freezing front reached deeper layers in the later freezing season, such uplift patterns related to elevations faded away.
The study encompasses wildfire-caused ground deformation in permafrost environments, through which, we aim to contribute to a more detailed understanding of the relationships between wildfire impacts and permafrost dynamics.