Utility of Classification and Regression Tree Analyses and Vegetation in Mountain Permafrost Models, Yukon, Canada

Geografiska Annaler: Series A, Physical Geography

Smith

et al. 2012

Self Cite

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.

Section: Discussionmentioning

confidence: 62%

“…5). Forested sites are mostly in spruce or mixed forest and can have open or closed canopies (see Kremer at al . 2011).…”

Section: Resultsmentioning

confidence: 99%

Spatial and thermal characteristics of mountain permafrost, northwest canada

Geografiska Annaler: Series A, Physical Geography

Smith

et al. 2012

Self Cite

“…Vegetation in the region comprises boreal forest with coniferous trees and some boreal broadleaf trees in lowland areas, while sub-alpine forest, shrubs, alpine tundra, barren patches, and exposed rock occur progressively at higher elevations (Wahl et al, 1987;Kremer et al, 2011). The northernmost portion of the study area is very close to an ecosystem boundary where vegetation begins to transition to arctic tundra with alpine sedges, grasses and shrubs dominating (Wahl et al, 1987).…”

Section: Study Regionmentioning

confidence: 99%

Impacts of mean annual air temperature change on a regional permafrost probability model for the southern Yukon and northern British Columbia, Canada

2013

The Cryosphere

Abstract. Air temperature changes were applied to a regional model of permafrost probability under equilibrium conditions for an area of nearly 0.5 × 10 6 km 2 in the southern Yukon and northwestern British Columbia, Canada. Associated environmental changes, including snow cover and vegetation, were not considered in the modelling. Permafrost extent increases from 58 % of the area (present day: 1971-2000) to 76 % under a −1 K cooling scenario, whereas warming scenarios decrease the percentage of permafrost area exponentially to 38 % (+ 1 K), 24 % (+ 2 K), 17% (+ 3 K), 12 % (+ 4 K) and 9 % (+ 5 K) of the area. The morphology of permafrost gain/loss under these scenarios is controlled by the surface lapse rate (SLR, i.e. air temperature elevation gradient), which varies across the region below treeline. Areas that are maritime exhibit SLRs characteristically similar above and below treeline resulting in low probabilities of permafrost in valley bottoms. When warming scenarios are applied, a loss front moves to upper elevations (simple unidirectional spatial loss). Areas where SLRs are gently negative below treeline and normal above treeline exhibit a loss front moving up-mountain at different rates according to two separate SLRs (complex unidirectional spatial loss). Areas that display high continentally exhibit bidirectional spatial loss in which the loss front moves up-mountain above treeline and down-mountain below treeline. The parts of the region most affected by changes in MAAT (mean annual air temperature) have SLRs close to 0 K km −1 and extensive discontinuous permafrost, whereas the least sensitive in terms of areal loss are sites above the treeline where permafrost presence is strongly elevation dependent.

“…Vegetation in the region comprises boreal forest with coniferous trees and some boreal broadleaf trees in lowland areas, while sub‐alpine forest, shrubs, alpine tundra, barren patches and exposed rock occur progressively at higher elevations (Wahl et al ., ; Kremer et al ., ). The northern‐most portion of the study area is very close to an ecosystem boundary where vegetation begins to transition to arctic tundra with alpine sedges, grasses and shrubs dominating (Wahl et al ., ).…”

Section: Study Regionmentioning

confidence: 99%

A Permafrost Probability Model for the Southern Yukon and Northern British Columbia, Canada

Permafrost & Periglacial

Kremer

et al. 2012

Self Cite

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.