Ground Surface Displacement After a Forest Fire Near Mayya, Eastern Siberia, Using InSAR: Observation and Implication for Geophysical Modeling.

Forest fires significantly impact permafrost degradation in the subarctic regions. However, interannual and seasonal variations in surface deformation due to permafrost thawing in burned areas were poorly understood. Measuring the ground surface displacement in fire scars helps us understand the freeze‐thaw dynamics of near‐surface ground and predict the future state, particularly in ice‐rich permafrost regions. This study used the L‐ and C‐band interferometric synthetic aperture radar technique to reveal interannual subsidence and seasonal thaw settlement/frost heave in a fire scar near Mayya, Sakha Republic in Eastern Siberia burned in 2013. We found that the cumulative subsidence was up to 7 cm between 2014 and 2020, most of which had occurred by 2016. The magnitude of seasonal thaw settlement and frost heave varied each year from 2017 to 2020 after the fire, but the interannual change in frost heave corresponded to the temporal variation in precipitation during the thawing season from 2017 to 2020. This suggests that the precipitation amount during the thawing season is related to the magnitude of segregation‐ice formation in the sediments, which determines the frost heave amount. The observed seasonal displacements could not be quantitatively explained by models inferred from the Stefan's equation and volume changes associated with ice‐water phase change. This implies that other models associated with segregated ice (ice lens) formation/thaw are required to explain the observed seasonal displacement. Plain Language Summary: Forest fires in permafrost regions significantly affect regional landscape changes and ecosystems through permafrost degradation and subsequent ground deformation. However, the number of observations of post forest fire surface displacement is extremely limited. We calculated surface displacement in a fire scar in Eastern Siberia from spaceborne radar images captured using interferometric synthetic aperture radar. Our observed data will help us understand permafrost degradation processes in forest fire scars. Key Points: Ground subsidence was primarily associated with the severity of forest fires, and slope orientation was likely an additional factorSeasonal frost heave measured by interferometric synthetic aperture radar was correlated to precipitation amount in thawing seasonExisting phase change model could not explain observed seasonal displacement quantitatively [ABSTRACT FROM AUTHOR]