Modification of the Snow Cover

Infrastructure in snowy, windy areas can modify snow cover distribution (Hestnes, 2000; Thiis and Jaedicke, 2000) and thus affect the thermal regime of the ground. Obstacles above the ground surface tend to cause the formation of local snow drifts and wind scoops, whereas avalanche defence structures and technical snow systems cause widespread artificial change in snow depth over large surface areas through prevention of avalanche formation or addition of snow, inducing a delay of snow melt in summer (Fig. 17). In the case of snow-supporting structures, a heterogeneous snow cover is formed because snow tends to accumulate above the structures and wind scoops form below. Modelling the long-term effects of this phenomenon shows a perturbation of the annual temperature regime and overall cooling of the ground during the design life of the structures (Phillips et al., 2000). Modern techniques of ski run preparation involve the use of technical snow, which can lead to long-term cooling of ground temperatures due to the higher density of such snow (Fauve et al., 2002), which is used by approximately 10-15% of ski resorts in the Alps. Rixen et al. (2004) suggest that at alpine sites where mean ground temperature is close to 0°C, the additional temperature reduction may suffice to induce permafrost formation. In areas where permafrost already exists, mechanical snow grooming and use of technical snow could help to conserve the permafrost. On the other hand, the cooling effects of technical snow may be countered by the removal of blocky rock material from ski runs (Haeberli, 1992). Some ski resorts in the Alps have recently started covering high altitude parts of ski runs with insulating material to prevent the snow from melting at all in summer (Fig. 16). The long-term effects of this type of treatment on the underlying or adjacent permafrost are as yet unknown.

Figure 17. Delayed melt of technical snow on ski runs above St. Moritz, Switzerland (M. Phillips).

Snow fences might have similar effects on the snow cover and hence this may destabilise the permafrost (e.g. Hinkel and Hurd, 2006). On the other hand, they can be used in a design to protect critical areas from snowdrift and the accumulation of thick snow cover, so that an effective heat extraction can be obtained during winter.

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