Transient thermal effects in Alpine permafrost

Abstract

Abstract. In high mountain areas, permafrost is important because it influences natural hazards and construction practices, and because it is an indicator of climate change. The modeling of its distribution and evolution over time is complicated by steep and complex topography, highly variable conditions at and below the surface, and varying climatic conditions. This paper presents a systematic investigation of effects of climate variability and topography that are important for subsurface temperatures in Alpine permafrost areas. The effects of both past and projected future ground surface temperature variations on the thermal state of Alpine permafrost are studied based on numerical experimentation with simplified mountain topography. For this purpose, we use a surface energy balance model together with a subsurface heat conduction scheme. The past climate variations that essentially influence the present-day permafrost temperatures at depth are the last glacial period and the major fluctuations in the past millennium. The influence of projected future warming was assessed to cause even larger transient effects in the subsurface thermal field because warming occurs on shorter time scales. Results further demonstrate the accelerating influence of multi-lateral warming in Alpine topography for a temperature signal entering the subsurface. The effects of thermal properties, porosity, and freezing characteristics were examined in sensitivity studies. A considerable influence of latent heat due to water in low-porosity bedrock was only shown for simulations over shorter time periods (i.e., decades to centuries). Finally, as an example of a real and complex topography, the modeled transient three-dimensional temperature distribution in the Matterhorn (Switzerland) is given for today and in 200 years.

Hydrology of the Upper Indus Basin Under Potential Climate Change Scenarios

“…Moreover, the hotter the summer is, the higher the scar elevation. The sharp contrast in scar elevation between north and south faces is also consistent with permafrost distribution (Noetzli et al 2007;Noetzli and Gruber 2009). Finally, rockfall especially affects topography prone to permafrost degradation such as pillars, spurs and ridges (Noetzli et al 2007).…”

Permafrost Studies in Kullu District, Himachal Pradesh

“…For example, other studies have recorded an increase in lower elevation limits of permafrost of up to 80 m in the Tibetan Plateau 7 , and up to 300 m in the Khumbu region of Nepal 18 since the 1970s. Such a significant shift implies that slopes within certain critical elevation zones have recently thawed completely, or are continuing to thaw at depth (owing to an offset between surface warming, and warming at depth 19 ), with implications for hazards and risk.…”

Mountain permafrost: development and challenges of a young research field

“…4) and accelerated by three-dimensional (3-D) geometry. The latter results from both multilateral warming and shorter distances to the surface, and makes mountain permafrost react significantly faster to surface changes than does permafrost in high-latitude lowlands (Noetzli and Gruber, 2009). The range of annual temperature variation measured in the borehole on the steep Hö rnliridge at the Matterhorn, Switzerland, for instance, is comparable to ranges measured at shallower depths at other sites, because the shortest distance to the surface is not to the top of the borehole (Nö tzli and Vonder Mü hll, 2010; Fig.…”

“…At larger depths (i.e. 500-1000 m), modelling results suggest effects may still exist within a range of a few degrees (Noetzli and Gruber, 2009). This is generally lower than in permafrost areas at lower altitudes due to comparably low ice contents and the abovedescribed accelerating effect of 3-D geometry.…”

“…Several candidate mechanisms for this connection of temperature and stability via permafrost degradation exist : loss of bonding, ice segregation, volume expansion, increased hydrostatic pressure and the reduction of shear strength. Warming and thawing of permafrost can arise from the direct interaction of the atmosphere and the rock surface or via changes in snow and ice cover (Fischer and others, 2006) and be propagated to depth by heat conduction (Noetzli and Gruber, 2009) or rapidly by heat convection with water flow (A. Hasler and others, unpublished information). Understanding the mechanisms and conditions that produce ice-filled clefts and fissures as well as understanding the environmental conditions and magnitudes of the processes linking temperature and stability are priorities to improve the ability to anticipate zones of future instability (Fischer, 2009).…”