Warming permafrost and active layer variability at Cime Bianche, Western European Alps

P Pogliotti,G Filippa,E Cremonese,U Morra Di Cella,M Guglielmin,C Hauck,C Pellet

doi:10.5194/tc-9-647-2015

Abstract

Abstract. The objective of this paper is to provide a first synthesis on the state and recent evolution of permafrost at the monitoring site of Cime Bianche (3100 m a.s.l.) on the Italian side of the Western Alps. The analysis is based on 7 years of ground temperature observations in two boreholes and seven surface points. The analysis aims to quantify the spatial and temporal variability of ground surface temperature in relation to snow cover, the small-scale spatial variability of the active layer thickness and current temperature trends in deep permafrost. Results show that the heterogeneity of snow cover thickness, both in space and time, is the main factor controlling ground surface temperatures and leads to a mean range of spatial variability (2.5 ± 0.1 °C) which far exceeds the mean range of observed inter-annual variability (1.6 ± 0.1 °C). The active layer thickness measured in two boreholes at a distance of 30 m shows a mean difference of 2.0 ± 0.1 m with the active layer of one borehole consistently deeper. As revealed by temperature analysis and geophysical soundings, such a difference is mainly driven by the ice/water content in the sub-surface and not by the snow cover regimes. The analysis of deep temperature time series reveals that permafrost is warming. The detected trends are statistically significant starting from a depth below 8 m with warming rates between 0.1 and 0.01 °C yr−1.

Highlights

The study of permafrost in mountain regions has become relevant in view of ongoing climate changes (Stoffel et al, 2014; Allen and Huggel, 2013; Etzelmüller, 2013; Fischer et al, 2013; Haeberli, 2013; Harris et al, 2009; Gruber and Haeberli, 2007; Gruber, 2004)
Some years (e.g., 2009, 2011, 2013) show a MAGST spatial variability, evaluated as the range of MAGST measured in all nodes and greater than 3 ◦C, that clearly exceeds the inter-annual variability
These observations confirm that the warming and cooling effects of, respectively, a thick and thin snow cover (Zhang, 2005; Pogliotti, 2010) can coexist over short distances (< 50 m) and lead to high spatial variability of the ground surface temperature (GST)

Summary

Introduction

The study of permafrost in mountain regions has become relevant in view of ongoing climate changes (Stoffel et al, 2014; Allen and Huggel, 2013; Etzelmüller, 2013; Fischer et al, 2013; Haeberli, 2013; Harris et al, 2009; Gruber and Haeberli, 2007; Gruber, 2004). For monitoring the huge spatial variability of mountain permafrost, a number of monitoring sites has been established through the Alps during the last years (e.g., Cremonese et al, 2011). The combination of geophysical methods and thermal monitoring is suitable for long-term monitoring of mountain permafrost because it provides crucial information on ground ice/water content and structure (e.g., Hilbich et al, 2008; Haeberli et al, 2010; PERMOS, 2013). The site of Cime Bianche has been designed with the main objective of monitoring the spatial variability of mountain permafrost. Cime Bianche site is a permanent observatory in the southern side of the European Alps, a region where permafrost observa-

Objectives

Results

Discussion

Conclusion