Articles | Volume 11, issue 1
The Cryosphere, 11, 585–607, 2017

Special issue: The evolution of permafrost in mountain regions

The Cryosphere, 11, 585–607, 2017
Research article
21 Feb 2017
Research article | 21 Feb 2017

Distributed snow and rock temperature modelling in steep rock walls using Alpine3D

Anna Haberkorn1,2, Nander Wever1,3, Martin Hoelzle2, Marcia Phillips1, Robert Kenner1, Mathias Bavay1, and Michael Lehning1,3 Anna Haberkorn et al.
  • 1WSL Institute for Snow and Avalanche Research SLF, 7260 Davos, Switzerland
  • 2Department of Geosciences, Unit of Geography, University of Fribourg, 1700 Fribourg, Switzerland
  • 3CRYOS, School of Architecture, Civil and Environmental Engineering, EPFL, 1015 Lausanne, Switzerland

Abstract. In this study we modelled the influence of the spatially and temporally heterogeneous snow cover on the surface energy balance and thus on rock temperatures in two rugged, steep rock walls on the Gemsstock ridge in the central Swiss Alps. The heterogeneous snow depth distribution in the rock walls was introduced to the distributed, process-based energy balance model Alpine3D with a precipitation scaling method based on snow depth data measured by terrestrial laser scanning. The influence of the snow cover on rock temperatures was investigated by comparing a snow-covered model scenario (precipitation input provided by precipitation scaling) with a snow-free (zero precipitation input) one. Model uncertainties are discussed and evaluated at both the point and spatial scales against 22 near-surface rock temperature measurements and high-resolution snow depth data from winter terrestrial laser scans.

In the rough rock walls, the heterogeneously distributed snow cover was moderately well reproduced by Alpine3D with mean absolute errors ranging between 0.31 and 0.81 m. However, snow cover duration was reproduced well and, consequently, near-surface rock temperatures were modelled convincingly. Uncertainties in rock temperature modelling were found to be around 1.6 °C. Errors in snow cover modelling and hence in rock temperature simulations are explained by inadequate snow settlement due to linear precipitation scaling, missing lateral heat fluxes in the rock, and by errors caused by interpolation of shortwave radiation, wind and air temperature into the rock walls.

Mean annual near-surface rock temperature increases were both measured and modelled in the steep rock walls as a consequence of a thick, long-lasting snow cover. Rock temperatures were 1.3–2.5 °C higher in the shaded and sunny rock walls, while comparing snow-covered to snow-free simulations. This helps to assess the potential error made in ground temperature modelling when neglecting snow in steep bedrock.

Short summary
The effects of permafrost degradation on rock slope stability in the Alps affect people and infrastructure. Modelling the evolution of permafrost is therefore of great importance. However, the snow cover has generally not been taken into account in model studies of steep, rugged rock walls. Thus, we present a distributed model study on the influence of the snow cover on rock temperatures. The promising results are discussed against detailed rock temperature measurements and snow depth data.