Modelling rock wall permafrost degradation in the Mont Blanc massif from the LIA to the end of the 21st century
Other literature type, Article
- Publisher: Copernicus Publications
(issn: 1994-0424, eissn: 1994-0424)
GE1-350 | QE1-996.5 | Environmental sciences | Geology
High alpine rock wall permafrost is extremely sensitive to climate change. Its degradation can trigger rock falls
constituting an increasing threat to socio-economical activities of highly frequented areas. Understanding of permafrost evolution is therefore crucial. This study investigates the long-term evolution of permafrost in three vertical cross-sections of rock wall sites between 3160 and 4300 m a.s.l. in the Mont Blanc massif, since LIA steady-state conditions to 2100. Simulations are forced with air temperature time series, including two contrasted air temperature scenarios for the 21<sup>st</sup> century representing possible lower and upper boundaries of future climate change according to the most recent models and climate change scenarios. The model outputs for the current period (2010–2015) are evaluated against borehole temperature measurements and an electrical resistivity transect: permafrost conditions are remarkably well represented. Along the past two decades, permafrost has disappeared into the S-exposed faces 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. Along the 21<sup>st</sup> century, warm permafrost is likely to extent at least up to 4300 m a.s.l. into the S-exposed rock walls, and up to 3850 m a.s.l. at depth of the N-exposed faces. In the most pessimistic case, permafrost will disappear at depth of the S-exposed rock walls up to 4300 m a.s.l., whereas warm permafrost will extend at depth of the N faces up to 3850 m a.s.l., but could disappear 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 the local topographical and transient effects. Shorter time-scale changes are not debatable due to limitations in the modelling approaches and future air temperature scenarios.