Canadian Forest Service Publications

Modeling hydrothermal regimes and potential impacts of climate change of permafrost within the South Mackenzie Plain, Northwest Territories, Canada. 2014. Jones, M.-F.; Castonguay, M.; Nasr, M.; Ogilvie, J.; Arp, P.A.; Bhatti, J. Ecoscience 21(1):21-33.

Year: 2014

Issued by: Northern Forestry Centre

Catalog ID: 35863

Language: English

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Available from the Journal's Web site.
DOI: 10.2980/21-1-3663

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Hydrothermal processes are key components of permafrost dynamics and hydrological and carbon cycles in northern forest ecosystems. A forest hydrology model, ForHyM, was used to evaluate these processes by determining how the depth and duration of frost penetration into the soil would vary daily over the course of several decades. This was done for chosen upland/wetland conditions within the Mackenzie Plain south of Fort Simpson, where permafrost is currently sporadic to discontinuous. The model calculations were done using daily weather records from November 1963 to 2010, starting with a hypothetical no-frost condition within the soil and subsoil. Model performance was evaluated by comparing modeled and measured temperatures at different soil depths (upland and peat plateau modelling, R2 = 0.95 and 0.94, respectively). It was found that well-drained upland forests within the general area would experience deep and complete freeze–thaw cycles each year. In contrast, poorly drained wetlands would develop gradually deepening permafrost that would at first stabilize in depth over the course of 10 to 20 y, with thaw depth limited to <1 m each year. However, recent increases in recorded air temperature (more so in winter than in summer) would destabilize the permafrost layer, and this would especially occur in areas with insufficient surface insulation by local peat, moss, forest litter, and snow accumulations. These estimates are consistent with (i) reported thawing depths and (ii) the widening encroachment of collapse scars towards the poorly drained portions of the South Mackenzie Plain.

Plain Language Summary

There is evidence that the permafrost in the Mackenzie Plain south of Fort Simpson is being degraded. This change is producing drastic changes in the landscape, including in the area’s vegetation. It has therefore become important to determine how the flow of moisture and heat through the soil is affecting freezing and thawing cycles. We used a forest hydrology model, ForHyM, to simulate soil moisture, heat, and frost under various types of insulating surface cover from barren soils to peat and forest. We used daily weather records from 1963 to 2010 to drive the model’s calculations. We found that the permafrost conditions near Fort Simpson are highly sensitive to changing air temperatures and changing amounts of on-the-ground snow: more snow means less freezing and more thawing. Frost penetration (and thawing) is further affected by the extent of forest vegetation and the amount of water in peaty soils. Our simulations are useful for quantifying existing and changing permafrost conditions and for projecting how these conditions may be affected by changes in climate and by disturbances such as forest fires, forestry, mineral exploitation, and road and corridor construction.