The effects of changes in climate and other environmental factors on permafrost evolution.

摘要

Permafrost is a product of a past colder climate. It underlies most of the terrestrial Arctic, where it influences landscape hydrology, biogeochemical environments and human activity. The current thermal regime of permafrost is mediated by different environmental factors, including snow, topography, vegetation and soil texture. The dependence of permafrost on these factors greatly complicates the modeling of permafrost dynamics. Accurate modeling of these dynamics, however, is critical for evaluating potential impacts of climate change on permafrost stability. The objectives of this study were to a) improve modeling of ground temperature during snow season; b) analyze the effects of post-fire environmental changes on permafrost thermal stability; and c) predict 21st century ground temperature dynamics in Alaska with high spatial resolution. To achieve the proposed objectives, near-surface air and ground temperatures were measured at permafrost observation stations across Alaska. Measured ground temperatures were used to evaluate simulated ground temperatures, which were generated with the Geophysical Institute Permafrost Laboratory (GIPL) numerical transient model. The current version of the GIPL model takes into account climate, snow, soil texture, soil moisture, and the freeze/thaw effect. To better model ground temperatures within the soil column, it was necessary to improve the parameterization of snow layer thermal properties in the GIPL model. To improve ground temperature simulations during snow season, daily snow thermal properties were estimated using an inverse approach. Modeling bias was improved by including ground temperatures simulated using estimated daily snow thermal conductivities. To address the effects of fire disturbance on permafrost thermal stability, we applied the GIPL model to lowland and upland boreal forest permafrost environments. The results indicate that permafrost vulnerability depends on pre-fire organic soil layer thickness and wetness, the amount of organic matter burned during the fire, and post-fire soil organic layer recovery rates. High spatial resolution permafrost maps are necessary for evaluating the potential impacts of permafrost thawing on Arctic ecosystems, engineering facilities, infrastructure, and the remobilization of soil carbon. Simulated ground temperatures in Alaska during the 21st century indicate widespread permafrost degradation in the discontinuous permafrost zone. High ground temperature warming trends are projected for most of the continuous permafrost zone north of the Brooks Range.