Estimating fire-induced permafrost thaw and carbon emissions from space

Arctic-boreal fire regimes are intensifying, leading to a growing number of boreal forest fires and Arctic tundra fires occuring on permafrost terrain. After fires, the seasonally thawed active layer of permafrost soils usually thickens, and this can lead to long-term gradual or abrupt permafrost degradation. Permafrost soils store large amounts of carbon, and hence fire-induced thaw may lead to additional carbon emissions from permafrost soils for many years after the fire.

This presentation explores several spaceborne measurements for mapping fire-induced permafrost thaw and its associated carbon emissions and will cover two case studies and one continental application. First, we investigated a boreal forest fire in Eastern Siberia using several measurements from sensors on Landsat 8. We found that especially land surface temperature (LST) related strongly to field-measured thaw depth, and we developed a statistical model to map fire-induced thaw depth over the entire fire scar. Second, we mapped post-fire permafrost soil subsidence after several tundra fires in Northeastern Siberia using Sentinel-1 interferometric synthetic aperture radar (InSAR) data. We found that burned areas experienced about three times higher soil subsidence than adjacent unburned areas in the growing season after the fire (4.88 cm/year vs. 1.54 cm/year), and this difference was primarily driven by fire-induced surface albedo darkening. Lastly, we used the ESA Climate Change Initiative permafrost product to estimate post-fire active layer thickening and associated carbon emissions for all fires in boreal North America between 2001 and 2019. We estimate that post-fire carbon emissions from permafrost thaw amount up to 30 % of the direct carbon emissions during fires, demonstrating the importance of including permafrost thaw when estimating climate feedbacks from boreal forest fires.

Taken together, this presentation highlights the use of multi-source remote sensing products for estimating post-fire surface deformation and active layer thickening of fires in permafrost ecosystems, and provides a first continental assessment of the climate warming feedback from carbon emissions from fire-induced permafrost thaw.