Permafrost is present at multiple elevations with no defined lower limit in the southern Yukon Territory, Canada. Empirical statistical modelling of permafrost probability in the region required the development of equivalent elevation, a new variable that reflects measured differences between surface air temperature lapse rates below and above treeline. In areas where surface lapse rates are negative (normal) but gentle up to the altitudinal treeline, equivalent elevation results in a compressed elevational range. Where surface lapse rates are positive (inverted) in the forest due to the strength of winter inversions, equivalent elevations calculated for valley floors are higher than those at treeline. There is a strong relationship between the magnitude and sign of surface lapse rates below treeline and the annual amplitude of monthly air temperatures at nearby climate stations, which permits prediction of equivalent elevation for the entire region. Permafrost probability modelling using equivalent elevation produced statistically significant results in several study areas whereas actual elevation values did not. The concept is of particular use where forested areas are underlain by permafrost and may be transferable to areas with similar terrain and climate such as those in the Canadian Northwest Territories, Alaska and Mongolia. Copyright © 2011 John Wiley & Sons, Ltd.

Lewkowicz, A.G., Bonnaventure, P.P., Smith, S.L. and Kuntz, Z., 2012. Spatial and thermal characteristics of mountain permafrost, northwest Canada. Geografiska Annaler: Series A, Physical Geography, ••, ••–••. doi:10.1111/j.1468‐0459.2012.00462.x ABSTRACT An extensive network of monitoring stations was used to develop a mean annual air temperature map for the complex mountainous terrain in the southern Yukon and northern British Columbia, Canada (latitude 59° to 65° N). Air temperature lapse rates measured at screen height from valley bottoms up to treeline are normal in the maritime extreme southwest, normal but weak in much of the region, and inverted in the highly continental northernmost sites. Relationships between air and ground surface temperatures, expressed as freezing and thawing n‐factors, vary significantly with vegetation type and hence elevational band, with the lowest values for the forested zone and the highest for non‐maritime alpine tundra. Equilibrium modelling carried out for one site in the southern part of the region and one in the northern part illustrates the impacts of the differing n‐factors on trends in mean ground surface temperature with elevation. Ground thermal regimes determined at borehole locations vary greatly due to these climatic controls but are also affected by substrate. Valley‐bottom permafrost in the south is scattered, at temperatures just below 0°C, has a depth of zero annual amplitude of 2–3 m (due to latent heat effects) and may be only a few metres in thickness. Permafrost on bedrock summits is cold, has active layers >5 m thick, is >50 m thick and may be locally continuous. Given the range of air temperatures and n‐factors, permafrost is possible throughout the Yukon but higher temperatures southward and stronger lapse rates mean that a lower elevational limit exists in northern British Columbia.

This paper provides a review of research and techniques that focus on the seasonally thawed portion of the Earth above permafrost terrain known as the active layer. The paper examines various different conceptual active layer systems, identifying five active layer types: bedrock (Type I), rock glacier or debris covered (Type II), mineral soil (Type III), organic mat or soil (Type IV) and submerged (Type V) active layer systems. These systems can be independent or mixed (frequently) in a permafrost environment, but all respond differently to climatic change or disturbance based on the thermal properties of the material and ice/water content. The review also highlights various active layer monitoring techniques including: probing, the Circumpolar Active Layer Monitoring Program (CALM) and frost tubes. Active layer modelling techniques are also reviewed, including the Stefan and the Kudryavtsev equations. In addition, the study highlights the active layer in a changing climate, examining the sensitivities of this layer to changes in temperature, precipitation and surface changes. Although the active layer has been well studied, knowledge gaps still exist including conflicting definitions between the thermal definition (0°C) and the physical definition (frozen water), which can become significant in areas with pore water that contains high levels of dissolved solids.

Permafrost maps are needed for infrastructure planning, climatic change adaptation strategies and northern development but often lack sufficient detail for these purposes. The high‐resolution (30 x 30 m grid cells) probability model for the southern Yukon and northern British Columbia presented in this paper (regional model) is a combination of seven local empirical‐statistical models, each developed from basal temperature of snow measurements in winter and ground‐truthing of frozen‐ground presence in summer. The models were blended using a distance‐decay power approach to generate a map of permafrost probability over an area of almost 500 000 km2 between 59°N and 65°N. The result is broadly similar to previous permafrost maps with an average permafrost probability of 58 per cent for the region as a whole. There are notable differences in detail, however, because the main predictive variable used in the local models is equivalent elevation, which incorporates the effects of gentle or inverted surface lapse rates in the forest zone. Most of the region shows permafrost distribution patterns that are non‐linear, resembling those from continental areas such as Mongolia. Only the southwestern area shows a similar mountain permafrost distribution to that in the European Alps with a well‐defined lower limit and a linear increase in probability with elevation. The results of the modelling can be presented on paper using traditional classifications into permafrost zones but given the level of detail, they will be more useful as an interactive online map. Copyright © 2012 John Wiley & Sons, Ltd.