ARC Funded Project

Masato Furuya

Affiliation: Hokkaido University
Project Title: Is post-fire thawed permafrost recovering after several decades?
Report:
　The high-latitude regions of the Northern Hemisphere are located within the “continuous permafrost zone,” where permafrost extends approximately one meter below the ground surface. It is estimated that permafrost contains more than twice as much organic carbon as the atmosphere, and there are concerns that its release into the atmosphere as a result of permafrost thaw could further accelerate global warming. While permafrost thaw can proceed gradually due to global warming, it can also occur abrupt as a result of disturbances to the ground surface. Forest fires are a prime example of such a factor, and reports indicate that the frequency and scale of fires themselves are on the rise due to global warming. Therefore, it is important to investigate the actual rate at which permafrost thaws due to forest fires; however, quantitative assessments have been lacking so far. This study investigated ground deformation at forest fire sites in the Yukon Territory of northwestern Canada over the past 50 years by analyzing satellite radar images. Although the radar image data were acquired over the past decade or so, the images include burned sites from various time periods. Therefore, by examining post-fire ground deformation, it is possible to investigate how permafrost thaws and recovers on a timescale of several decades. The figure shows ground deformation since 2017 (right) at burned and un-burned sites (left) from 1986, 2004, and 2017. While the 2017 fire scar is subsiding rapidly, the 2004 fire scar is slowly rising, strongly suggesting that thawing is progressing at the former and permafrost recovery is occurring at the latter. This series of processes is thought to be governed by the loss and recovery of surface vegetation. Additionally, while the 1986 fire site appears to be nearly stable, the non-fire site also shows slow subsidence.