Long-term and seasonal surface displacement after wildfires in Mayya, Central Yakutia, revealed by ALOS-2 and Sentinel-1 SAR Interferometry

Wildfires are known to have great impact on arctic permafrost regions in terms of not only causing permafrost degradation but also atmospheric and biological environments. Given the fact that permafrost thaw release soil organic carbon as greenhouse gases and it can be positive feedback on global warming (Shuur et al., 2015), it is essential to know how much permafrost thaws to clarify the carbon budget after wildfires. Although number of wildfires in Eastern Siberia has recently been increasing, field observation data are quite limited and mechanism of thermokarst development after wildfire is poorly understood.

Interferometric Synthetic Aperture Radar (InSAR) has been used to monitor post-wildfire surface deformation in Alaska and Eastern Siberia (e.g., Liu et al., 2014; Molan et al., 2018; Michaelides et al., 2019; Yanagiya and Furuya, 2020). However, number of studies on temporal changes in the spatial distribution of seasonal and long-term displacements after wildfires is quite limited, and the temporal changes immediately after wildfires especially remain uncertain.

In this study, we focused on two wildfires in 2013 and 2018, in Mayya, Central Yakutia, to investigate post-wildfire surface deformations by ALOS-2 L-band and Sentinel-1 C-band InSAR. SBAS time-series analysis using ALOS-2 data showed that cumulative subsidence in the 2013 fire area was up to 6 cm in 2014-2020, whose subsidence trend decreased exponentially. The Sentinel-1 images indicated seasonal displacements of thaw subsidence and frost upheaval in 2016-2020, but a few interferograms in between April and May showed significant coherence loss, which did not enable to detect surface displacement in the period. Seasonal amplitudes in 2016-2020 by the Sentinel-1 InSAR were approximately 5.5 cm, decreasing over time, but the amplitudes immediately after the wildfire in 2013-2015 was uncertain. In the 2018 fire, cumulative subsidence of 2.5 cm in 2018-2020 was detected by ALOS-2, and seasonal amplitudes of surface displacement in 2018 and 2019 were 3.7 and 3.8 cm. The two study cases will help to better understand permafrost thaw dynamics encouraged by wildfires.