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Arctic Science 2000 - Crossing Borders: Science and Community
Whitehorse, Yukon, Canada, Sept 21-24 2000
American Association for the Advancement of Science & Yukon Science Institute

Investigations of the Response of Permafrost to Climate Change, Takhini River Valley, YT.

Near-surface ground temperatures have been measured at several sites in Takhini valley, 50 km west of Whitehorse, since 1983. The purpose of the monitoring program is to determine the response of "warm" permafrost in this part of the sporadic discontinuous permafrost zone to climatic variation. During 1997-2000 a field experiment has been conducted to determine the response of permafrost to changes in snow cover, since this variable is critical to the ground thermal regime.

Ground temperatures to 5 m depth are measured each fortnight on calibrated thermistors in stalled in 2.5 cm (OD) steel pipe at three sites. One is in an undisturbed forest where permafrost is 16 m thick and has a near-surface mean annual temperature of –1.1ºC (site 1); another is in an area burned by forest fire in 1958, where permafrost is degrading (site 2); the third is a meadow, where the ground is permafrost-free (site 3). Air temperatures are measured at sites 1 and 2 by HOBO miniature loggers placed in radiation shields. Three cables have been installed in the meadow for the snow-depth investigations. The snow is cleared from one throughout the winter, snow depth is enhanced at another by a snow fence, and is left undisturbed at the third.

Daily mean air temperatures at open sites in Takhini valley are about 1ºC cooler than at Whitehorse Airport, and about 2ºC in forest areas. Monthly mean air temperatures recorded since 1983 at Whitehorse Airport show considerable variation in winter, but conditions in summer have been relatively consistent. Enhanced climate change is expected in winter at high latitudes, but seasonal effects may be even greater in southern Yukon due to a reduction in efficacy of the coastal mountains in blocking maritime systems from the region. The permafrost temperature record indicates general stability over the last 15 years, with slight cooling associated with recent cold winters. Permafrost stability is associated with (1) the dry soils of the area, which have a relatively low thermal conductivity, and (2) its presence beneath forests, which intercept snow in winter. The general aridity of the area implies that there is relatively little opportunity for convective heat flow at the sites.

At the experimental site, snow clearing over 3 winters has lowered the mean annual ground temperature by nearly 1.5ºC. The impact of such cooling is most evident in summer, because the extra heat required for ground warming at depth leads to cooler near-surface temperatures. Winter ground temperatures are higher near the snow fence, but cooler in spring, due to prolonged snow melt and an enhanced evaporative flux.

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