Semi-automated calibration method for modelling of mountain permafrost evolution in Switzerland

Antoine Marmy,Nadine Salzmann,Marcia Phillips,Christian Hauck,Christin Hilbich,Jan Rajczak,Martin Hoelzle,Reynald Delaloye,Sven Kotlarski,Jeannette Noetzli,Christophe Lambiel,Benno Staub

doi:10.5194/tc-10-2693-2016

Abstract

Abstract. Permafrost is a widespread phenomenon in mountainous regions of the world such as the European Alps. Many important topics such as the future evolution of permafrost related to climate change and the detection of permafrost related to potential natural hazards sites are of major concern to our society. Numerical permafrost models are the only tools which allow for the projection of the future evolution of permafrost. Due to the complexity of the processes involved and the heterogeneity of Alpine terrain, models must be carefully calibrated, and results should be compared with observations at the site (borehole) scale. However, for large-scale applications, a site-specific model calibration for a multitude of grid points would be very time-consuming. To tackle this issue, this study presents a semi-automated calibration method using the Generalized Likelihood Uncertainty Estimation (GLUE) as implemented in a 1-D soil model (CoupModel) and applies it to six permafrost sites in the Swiss Alps. We show that this semi-automated calibration method is able to accurately reproduce the main thermal condition characteristics with some limitations at sites with unique conditions such as 3-D air or water circulation, which have to be calibrated manually. The calibration obtained was used for global and regional climate model (GCM/RCM)-based long-term climate projections under the A1B climate scenario (EU-ENSEMBLES project) specifically downscaled at each borehole site. The projection shows general permafrost degradation with thawing at 10 m, even partially reaching 20 m depth by the end of the century, but with different timing among the sites and with partly considerable uncertainties due to the spread of the applied climatic forcing.

Highlights

Permafrost is the thermal state of a soil or rock subsurface with a temperature that remains below 0 ◦C for two or more consecutive years (Harris et al, 2009)
The increase in air temperatures observed in the last decades (Mountain Research Initiative EDW Working Group, 2015) has had notable effects on permafrost that are apparent: (i) in the borehole data series by higher surface and subsurface ground temperatures and significantly deeper active layers (e.g. PERMOS, 2016), (ii) in geophysical data with a decrease of the electrical resistivities
Other goals were to analyse the sensitivity of the model results to certain parameters, to identify site-specific processes that play a major role in the thermal regime at the individual permafrost sites and to use the calibrated model set-ups for long-term regional climate model (RCM)-based simulations of the permafrost evolution

Summary

Introduction

Permafrost is the thermal state of a soil or rock subsurface with a temperature that remains below 0 ◦C for two or more consecutive years (Harris et al, 2009). It occurs in the Arctic (Romanovsky et al, 2010) and Antarctic icefree regions (Vieira et al, 2010) as well as in mid-latitude mountain ranges such as in the European Alps (Boeckli et al, 2012), the Andes (Trombotto, 2000) and the Himalayan range (Weiming et al, 2012). Anthony et al, 2012), engineering and construction issues Marmy et al.: Semi-automated calibration of mountain permafrost evolution model et al, 2008, 2011; PERMOS, 2016) and of seismic velocities (Hilbich, 2010), indicating a reduction of ice content, and (iii) in the increased activity of permafrost creep (Kääb and Kneisel, 2006; Barboux et al, 2013) and increased velocities of instable rock glaciers (Kääb et al, 2007; Gärtner-Roer, 2012)

Methods

Findings

Discussion

Conclusion