| Popis: |
The warming and degradation of mountain permafrost within alpine areas is an important process influencing the stability of steep slopes and rock faces. In the mountains of southern Norway (Jotunheimen), an increase in ground temperatures has been recorded during the last 12 years, and modelling studies suggest the possible degradation of most mountain permafrost during the 21st century. To better estimate the thermal state of permafrost in steep rock walls in Norway, five temperature loggers were installed in 2009 and 2010, measuring the near-surface rock wall temperatures in vertical rock faces. Surface temperatures in rock walls in Norway are on average higher than the ambient air temperature, by about 1 °C in shaded faces to more than 3 °C in faces with other aspects. An aspect dependency of rock wall temperatures is mainly visible during summer, with deviations of up to 4 °C between north- and south-facing walls. Based on a 1D transient heat flow model, the active-layer thickness at the study sites was estimated to be in the range of 3 m to 5 m at 2300 m asl and 1600 m asl, respectively. As a first-order approximation, a spatial regression model based on elevation and potential incoming short-wave radiation was used to estimate the lower limit and distribution of rock wall permafrost under present-day conditions and for a scenario with average air temperatures increased by 2 °C. Today, the lower limit ranges from 1200–1300 m asl to 1600–1700 m asl in north- and south-facing rock walls, respectively. With a warming of 2 °C, the lower limit would increase to about 1700 m and 2100 m, respectively, which corresponds to a loss of 70 per cent of the rock walls underlain by permafrost today in the study area, where more than half of the rock walls potentially containing permafrost are situated below 1800 m asl. Copyright © 2014 John Wiley & Sons, Ltd. |
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