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The Cryosphere An interactive open-access journal of the European Geosciences Union
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Preprints
https://doi.org/10.5194/tc-2020-42
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/tc-2020-42
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  21 Feb 2020

21 Feb 2020

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A revised version of this preprint was accepted for the journal TC and is expected to appear here in due course.

On the importance of snowpack stability, its frequency distribution, and avalanche size in assessing the avalanche danger level: a data-driven approach

Frank Techel1,2, Karsten Müller3, and Jürg Schweizer1 Frank Techel et al.
  • 1WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • 2University of Zurich, Department of Geography, Zurich, Switzerland
  • 3Norwegian Water Resources and Energy Directorate NVE, Oslo, Norway

Abstract. Consistency in assigning an avalanche danger level when forecasting or locally assessing avalanche hazard is essential, but challenging to achieve, as relevant information is often scarce and must be interpreted in the light of uncertainties. Furthermore, the definitions of the danger levels, an ordinal variable, are vague and leave room for interpretation. Decision tools, developed to assist in assigning a danger level, are primarily experience-based due to a lack of data. Here, we address this lack of quantitative evidence by exploring a large data set of stability tests (N = 10,125) and avalanche observations (N = 39,017) from two countries related to the three key factors that characterize avalanche danger: snowpack stability, its frequency distribution and avalanche size. We show that the frequency of the most unstable locations increases with increasing danger level. However, a similarly clear relation between avalanche size and danger level was not found. Only for the higher danger levels the size of the largest avalanche per day and warning region increased. Furthermore, we derive stability distributions typical for the danger levels 1-Low to 4-High using four stability classes (very poor, poor, fair and good), and define frequency classes (none or nearly none, a few, several and many) describing the frequency of the most unstable locations. Combining snowpack stability, its frequency and avalanche size in a simulation experiment, typical descriptions for the four danger levels are obtained. Finally, using the simulated snowpack distributions together with the largest avalanche size in a step-wise approach, as proposed in the Conceptual Model of Avalanche Hazard, we present an example for a data-driven look-up table for avalanche danger assessment. Our findings may aid in refining the definitions of the avalanche danger scale and in fostering its consistent usage.

Frank Techel et al.

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Frank Techel et al.

Frank Techel et al.

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Latest update: 27 Sep 2020
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Short summary
The avalanche danger scale qualitatively describes the five ordinal danger levels. However, descriptions are vague and leave room for interpretation. We explore a large data set of stability tests and avalanche observations to quantitatively describe the three key factors that characterize avalanche danger: snowpack stability, its frequency distribution and avalanche size. We hope our findings will aid in refining the definitions of the avalanche danger scale and in fostering its consistent use.
The avalanche danger scale qualitatively describes the five ordinal danger levels. However,...
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