Post‐Wildfire Surface Deformation Near Batagay, Eastern Siberia, Detected by L‐Band and C‐Band InSAR

• Published in: Journal of geophysical research. Earth surface 2020-07, Vol.125 (7), p.n/a
• Main Authors: Yanagiya, Kazuki, Furuya, Masato
• Format: Article
• Language: English
• Subjects: Active layer; ALOS2; Arctic zone; C band; Deformation; Evolution; Freezing; Frost; Frost heaving; Gullies; Heaving; Ice environments; Imaging techniques; InSAR; Interferometric synthetic aperture radar; Interferometry; Landforms; Microwave sensors; Permafrost; Pore water; Premelting dynamics; Radar; SAR (radar); Satellites; Sentinel‐1; Slopes; Soil degradation; Subsidence; Synthetic aperture radar; Synthetic aperture radar interferometry; Temporal resolution; Thawing; Thermokarst; Wildfire; Wildfires
• ISSN: 2169-9003; 2169-9011
• DOI: 10.1029/2019JF005473

Thawing of ice‐rich permafrost and subsequent ground subsidence can form characteristic landforms, and the resulting topography they create is collectively called “thermokarst.” The impact of wildfire on thermokarst development remains uncertain. Here, we report on the post‐wildfire ground deformation associated with the 2014 wildfire near Batagay, Eastern Siberia. We used Interferometric Synthetic Aperture Radar (InSAR) to generate both long‐term (1–4 years) and short‐term (subseasonal to seasonal) deformation maps. Based on two independent satellite‐based microwave sensors, we could validate the dominance of vertical displacements and their heterogeneous distributions without relying on in situ data. The inferred time series based on L‐band ALOS2 InSAR data indicated that the cumulative subsidence at the area of greatest magnitude was greater than 30 cm from October 2015 to June 2019 and that the rate of subsidence slowed in 2018. The burn severity was rather homogeneous, but the cumulative subsidence magnitude was larger on the east‐facing slopes where the gullies were also predominantly developed. The correlation suggests that the active layer on the east‐facing slopes might have been thinner before the fire. Meanwhile, C‐band Sentinel‐1 InSAR data with higher temporal resolution showed that the temporal evolution included episodic changes in terms of deformation rate. Moreover, we could unambiguously detect frost heave signals that were enhanced within the burned area during the early freezing season but were absent in the mid‐winter. We could reasonably interpret the frost heave signals within a framework of premelting theory instead of assuming a simple freezing and subsequent volume expansion of preexisting pore water. Plain Language Summary Wildfires in arctic regions show not only an immediate impact on nearby residents but also long‐lasting effects on both regional ecosystems and landforms of the burned area via permafrost degradation and subsequent surface deformation. However, the observations of post‐wildfire ground deformations have been limited. Using satellite‐based imaging technique called Interferometric Synthetic Aperture Radar (InSAR), we detected the detailed spatial‐temporal evolution of post‐wildfire surface deformation in Eastern Siberia, which helps in understanding permafrost degradation processes over remote areas. Post‐wildfire areas are likely to be focal points of permafrost degradation in the Arctic that can last many years.