Document Type

Thesis

Degree Name

Master of Science (MSc)

Department

Geography & Environmental Studies

Faculty/School

Faculty of Arts

First Advisor

William Quinton

Advisor Role

Supervisor

Abstract

During the past century, the highest rates of warming have occurred at latitudes above 60oN, where air temperatures have risen at twice the rate of other regions. In northwestern Canada, this warming has coincided with an increase in the frequency, size and severity of wildfires. The influence of such fires on the trajectory of on-going permafrost thaw is not well understood. As a consequence, the combined impacts of climate warming induced permafrost thaw and possible feedbacks arising from wildfires cannot be properly assessed. This study examines the impact of a 2.7 ha low-severity wildfire (July 2014) on water and energy flow processes that affect the timing and magnitude of ground thaw, including seasonal ground thaw, talik development and permafrost thaw. By comparing the end-of-winter snow water equivalent (SWE), rate of snowmelt and surface energy balance one year post-fire (2015) on an adjacent burned and unburned portions of a forested permafrost peat plateau as well as ground thaw and soil moisture three years post-fire (2015-2017).

Increase (16%) in snow depth had no significant direct impact on the increased rate and depth of ground thaw. Rather the increase in thaw depths resulted from a combination of factors: a longer thawing period due to an earlier (4 days) snowpack disappearance, an increase in energy available for snowmelt (36%) attributable to greater incoming shortwave radiation from the loss of radiative filtering provided by the canopy, decreased albedo and increased emitted longwave radiation from the charred trunks, contributing to the warmer soil temperatures at greater depths. Bulk thermal conductivity is lower in the burned forest soil as a result of drier soils. Thaw depths in the burned forest are significantly greater than thaw depths in the unburned forest, suggesting that the increased energy availability outweighs the impacts of a drier soil. Ground temperatures at 64 cm did not cool beyond the freezing point depression (-0.3℃), indicating an incomplete overwinter refreezing at this depth leading to the development of taliks.

Given the current warming trend in northwestern Canada, and that permafrost in this region is thin (< 10 m) and relatively warm (> -1°C), perturbation caused by a low-severity fire appears to be strong enough to induce talik development. In a peatland terrain underlain by discontinuous permafrost, talik development can sufficiently alter the thermal regime enough to trigger complete permafrost thaw. This study showed that a fire can change the amount of snow accumulation, the rate of its melt and disappearance, and the rate and pattern of ground thaw, which collectively alter key water flow and storage processes throughout the burned area.

Convocation Year

2018

Convocation Season

Fall

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