Modelling rock wall permafrost degradation in the Mont Blanc massif from the LIA to the end of the 21st century

Abstract

Abstract. High alpine rock wall permafrost is extremely sensitive to climate change. Its degradation has a strong impact on landscape evolution and can trigger rockfalls constituting an increasing threat to socio-economical activities of highly frequented areas; quantitative understanding of permafrost evolution is crucial for such communities. This study investigates the long-term evolution of permafrost in three vertical cross sections of rock wall sites between 3160 and 4300 m above sea level in the Mont Blanc massif, from the Little Ice Age (LIA) steady-state conditions to 2100. Simulations are forced with air temperature time series, including two contrasted air temperature scenarios for the 21st century representing possible lower and upper boundaries of future climate change according to the most recent models and climate change scenarios. The 2-D finite element model accounts for heat conduction and latent heat transfers, and the outputs for the current period (2010)(2011)(2012)(2013)(2014)(2015) are evaluated against borehole temperature measurements and an electrical resistivity transect: permafrost conditions are remarkably well represented. Over the past two decades, permafrost has disappeared on faces with a southerly aspect up to 3300 m a.s.l. and possibly higher. Warm permafrost (i.e. > −2 • C) has extended up to 3300 and 3850 m a.s.l. in N and S-exposed faces respectively. During the 21st century, warm permafrost is likely to extend at least up to 4300 m a.s.l. on S-exposed rock walls and up to 3850 m a.s.l. depth on the N-exposed faces. In the most pessimistic case, permafrost will disappear on the S-exposed rock walls at a depth of up to 4300 m a.s.l., whereas warm permafrost will extend at a depth of the N faces up to 3850 m a.s.l., but possibly disappearing at such elevation under the influence of a close S face. The results are site specific and extrapolation to other sites is limited by the imbrication of local topographical and transient effects.

Rockslides and rock avalanches in the Central Andes of Argentina and their possible association with permafrost degradation

“…For example, in the Aiguille du Midi and Grand Montets mountain peaks (France),Magnin et al 15 concluded that since the Little Ice Age (LIA), the thermal perturbation induced by climate change reached 60-70 m below the rock surface (using a +1°C interpolated warming trend), while between the 1990s and 2010s, cold permafrost disappeared from south-exposed (warm) slopes, while warm permafrost extended up to shallow layers (10 m depth below the surface) in north-exposed slopes. Based on the positive MAAT trend (0.004°C/yr) calculated for the Central Andes, and historical calculation of a predominance of freezing/thawing air conditions,25 we hypothesize that similar conditions, as portrayed by Magnin et al,15 are currently taking place in the study area. However, short-term climatic oscillations (seasonal, annual or decadal) may be superimposed, both in time and in space, on long-term processes, build over hundreds or thousands of years.…”

“…However, only punctuated and relatively short ground‐temperature time series are available for rock walls. For example, in the Aiguille du Midi and Grand Montets mountain peaks (France), Magnin et al . concluded that since the Little Ice Age (LIA), the thermal perturbation induced by climate change reached 60–70 m below the rock surface (using a +1°C interpolated warming trend), while between the 1990s and 2010s, cold permafrost disappeared from south‐exposed (warm) slopes, while warm permafrost extended up to shallow layers (10 m depth below the surface) in north‐exposed slopes.…”

The impact of land surface temperatures on suprapermafrost groundwater on the central Qinghai‐Tibet Plateau

“…In our modelling procedure, we use the hydrogeological software DHI‐WASY FEFLOW to simulate the runoff process in the active layer. Numerical calculations of the two‐dimensional water flow in porous media of variable saturation in FEFLOW are based on the standard forms of Darcy's and Richards' equations (Daemi & Krol, ; Diersch, Bauer, Heidemann, Rühaak, & Schätzl, ; Magnin et al, ): where q i is the groundwater flux vector (m/s); h is the water pore pressure head (m); K ij is the hydraulic conductivity tensor (m/s); and Q is the sink or source term (1/s); i , j = 1, 2.…”

“…Numerical calculations of the two-dimensional water flow in porous media of variable saturation in FEFLOW are based on the standard forms of Darcy's and Richards' equations (Daemi & Krol, 2019;Diersch, Bauer, Heidemann, Rühaak, & Schätzl, 2011;Magnin et al, 2017):…”

Monitoring permafrost and periglacial processes in Sierra Nevada (Spain) from 2001 to 2016

“…This temperature increase since the end of the LIA is much more pronounced in the mountain areas than in the lowlands, which has led to changes in the intensity and spatial distribution of cold geomorphological processes . It has also resulted in an intensification of the paraglacial response, an accelerated degradation of alpine permafrost, and alterations in biogeographic dynamics in European high mountain environments, with a geographic redistribution of some plant species that tend to move up to higher altitudes . In the Sierra Nevada, due to its latitudinal position and geographical characteristics, changes resulting from the end of the LIA still have a significant impact on ecosystem dynamics typical of high semi‐arid Mediterranean mountains.…”