Modeling Maximum Active Layer Thaw in Boreal and Tundra Environments using Limited Data

The variability of maximum active layer thaw in boreal and tundra environments has important implications for hydrologic processes, terrestrial and aquatic ecosystems, and the integrity of northern infrastructure, including oil and gas pipelines. For most planning and management purposes, the long-term probability distribution of active layer thickness is of primary interest. This study presents a robust method for calculating maximum active layer thaw, employing Stefan’s equation to compute phase change of the moisture in soils and using air temperature as the sole climatic forcing variable to drive the model. Near-surface ground temperatures, representing the boundary condition for Stefan’s algorithm, were estimated based on empirical relationships established for several sites in the Mackenzie Valley. Active layer thaw simulations were performed for typically saturated soils (one with 0.2 m peat overlying mineral substrate and one with 1.0 m peat) in tundra and in boreal forest environments. The results permit an evaluation of the probability distributions of maximum active layer thaw for different locations in permafrost terrain.