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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
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Volume 18, issue 10 | Copyright
Nat. Hazards Earth Syst. Sci., 18, 2697-2716, 2018
https://doi.org/10.5194/nhess-18-2697-2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 23 Oct 2018

Research article | 23 Oct 2018

Spatial consistency and bias in avalanche forecasts – a case study in the European Alps

Frank Techel1,2, Christoph Mitterer5, Elisabetta Ceaglio3, Cécile Coléou4, Samuel Morin6,8, Francesca Rastelli7, and Ross S. Purves2 Frank Techel et al.
  • 1WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland
  • 2Department of Geography, University of Zürich, Zurich, Switzerland
  • 3Fondazione Montagna sicura, Ufficio neve e valanghe, Regione Autonoma Valle d'Aosta, Italy
  • 4Météo France, Direction des Opérations pour la Prévision, Cellule Montagne Nivologie, Grenoble, France
  • 5Lawinenwarndienst Tirol, Abteilung Zivil- und Katastrophenschutz, Innsbruck, Austria
  • 6Météo France – CNRS, CNRM UMR 3589, Centre d'Études de la Neige, Grenoble, France
  • 7Meteomont Carabinieri, Bormio, Italy
  • 8Université Grenoble Alpes, Université de Toulouse, Toulouse, France

Abstract. In the European Alps, the public is provided with regional avalanche forecasts, issued by about 30 forecast centers throughout the winter, covering a spatially contiguous area. A key element in these forecasts is the communication of avalanche danger according to the five-level, ordinal European Avalanche Danger Scale (EADS). Consistency in the application of the avalanche danger levels by the individual forecast centers is essential to avoid misunderstandings or misinterpretations by users, particularly those utilizing bulletins issued by different forecast centers. As the quality of avalanche forecasts is difficult to verify, due to the categorical nature of the EADS, we investigated forecast goodness by focusing on spatial consistency and bias, exploring real forecast danger levels from four winter seasons (477 forecast days). We describe the operational constraints associated with the production and communication of the avalanche bulletins, and we propose a methodology to quantitatively explore spatial consistency and bias. We note that the forecast danger level agreed significantly less often when compared across national and forecast center boundaries (about 60%) than within forecast center boundaries (about 90%). Furthermore, several forecast centers showed significant systematic differences in terms of more frequently using lower (or higher) danger levels than their neighbors. Discrepancies seemed to be greatest when analyzing the proportion of forecasts with danger level 4 – high and 5 – very high. The size of the warning regions, the smallest geographically clearly specified areas underlying the forecast products, differed considerably between forecast centers. Region size also had a significant impact on all summary statistics and is a key parameter influencing the issued danger level, but it also limits the communication of spatial variations in the danger level. Operational constraints in the production and communication of avalanche forecasts and variation in the ways the EADS is interpreted locally may contribute to inconsistencies and may be potential sources for misinterpretation by forecast users. All these issues highlight the need to further harmonize the forecast production process and the way avalanche hazard is communicated to increase consistency and hence facilitate cross-border forecast interpretation by traveling users.

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In 1993, the European Avalanche Warning Services agreed upon a common danger scale to describe the regional avalanche hazard: the European Avalanche Danger Scale. Using published avalanche forecasts, we explored whether forecasters use the scale consistently. We noted differences in the use of the danger levels, some of which could be linked to the size of the regions a regional danger level is issued for. We recommend further harmonizing the avalanche forecast products in the Alps.
In 1993, the European Avalanche Warning Services agreed upon a common danger scale to describe...
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