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TitleBoreal permafrost thaw amplified by fire disturbance and precipitation increases
AuthorWilliams, M; Zhang, YORCID logo; Estop-Aragonés, C; Fisher, J P; Xenakis, G; Charman, D J; Hartley, I P; Murton, J B; Phoenix, G K
SourceEnvironmental Research Letters vol. 15, no. 11, 114050, 2020 p. 1-13, Open Access logo Open Access
Alt SeriesNatural Resources Canada, Contribution Series 20200608
PublisherIOP Publishing Ltd.
Mediapaper; on-line; digital
File formatpdf; html
Subjectssurficial geology/geomorphology; soils science; environmental geology; Nature and Environment; Science and Technology; organic carbon; permafrost; soil moisture; vegetation; climate effects; precipitation; soils; soil moisture; modelling; thermal regimes; temperature; ground temperatures; terrain sensitivity; Climate change; Boreal ecosystems; Forests; Trees; Biology; Forest fires; permafrost thaw; Hydrology; cumulative effects
Illustrationstables; profiles; time series; plots
ProgramCanada Centre for Remote Sensing Optical methods and applications
Released2020 11 18
AbstractPermafrost soils store huge amounts of organic carbon, which could be released if climate change promotes thaw. Currently, modelling studies predict that thaw in boreal regions is mainly sensitive to warming, rather than changes in precipitation or vegetation cover. We evaluate this conclusion for North American boreal forests using a detailed process-based model parameterised and validated on field measurements. We show that soil thermal regimes for dominant forest types are controlled strongly by soil moisture and thus the balance between evapotranspiration and precipitation. Under dense canopy cover, high evapotranspiration means a 30% increase in precipitation causes less thaw than a 1 C increase in temperature. However, disturbance to vegetation promotes greater thaw through reduced evapotranspiration, which results in wetter, more thermally conductive soils. In such disturbed forests, increases in precipitation rival warming as a direct driver of thaw, with a 30% increase in precipitation at current temperatures causing more thaw than 2 C of warming. We find striking non-linear interactive effects on thaw between rising precipitation and loss of leaf area, which are of concern given projections of greater precipitation and disturbance in boreal forests. Inclusion of robust vegetation-hydrological feedbacks in global models is therefore critical for accurately predicting permafrost dynamics; thaw cannot be considered to be controlled solely by rising temperatures.
Summary(Plain Language Summary, not published)
This article focuses on the permafrost soils in North American boreal forests. These soils store a lot of organic carbon, which can be released into the atmosphere if the permafrost thaws due to climate change. Current modeling studies suggest that the thaw in these regions is primarily influenced by temperature increases, not so much by changes in precipitation or vegetation.
However, this research challenges that idea. Using a detailed model based on real-world measurements, the scientists found that soil moisture plays a crucial role in determining permafrost thaw. Under dense forest canopies, where there's a lot of evapotranspiration (water movement from the ground into the atmosphere), a 30% increase in precipitation has less of an impact on thaw than a 1°C temperature rise.
But, when there's disturbance to the vegetation (like deforestation), it reduces evapotranspiration, making the soil wetter and more conducive to thaw. In these disturbed forests, more precipitation has a significant thawing effect, potentially equal to a 2°C temperature increase.
This study highlights the complex interactions between rising precipitation, changes in vegetation, and permafrost thaw. It emphasizes the need to include these factors in global climate models to accurately predict permafrost dynamics, as thaw isn't solely determined by temperature increases. This research is essential in understanding how climate change affects these critical ecosystems.

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