Réf. Schneebeli & al. 1997 - A

Référence bibliographique complète
SCHNEEBELI M., LATERNSER M. & AMMANN W. Destructive snow avalanches and climate change in the Swiss Alps. Eclogae geol. Helv.,1997, vol. 90, 457-461.

Abstract: This study investigates the relations of climatic conditions on avalanche release from 1947-1993 and extreme snowfall events from 1896-1993. The statistical evaluation of the meteorological data shows a long-term trend in temperature, but not in snow depth and extreme snowfall events. From the meteorological long-term time series at Davos (eastern Switzerland) we tried to model the corresponding avalanche activity from 1896-1946. The modelling of the avalanche activity was not successful because the extremely sparse distribution of extreme events prevented the establishment of a reliable statistical model. Looking at potential avalanche situations in terms of extreme weather situations it can be assumed that the climatic causes for severe avalanche periods have remained stable during the past 100 years and show no sign of change in the near future. However, the construction of defence structures in avalanche starting zones, improved zoning of hazardous areas and artificial avalanche release have reduced the probability of catastrophic events.

Mots-clés
 Long term trend, snow depth, defence structues, probability, snow avalanches, climate change.

Organismes / Contact
Swiss Federal Institute for Snow and Avalanche Research SLF, CH-7260 Davos Dorf
(From the symposium "Natural Hazards" in the framework of the symposium Global Change of the Swiss-Academy of Natural Sciences, Zurich, 10-11 sept. 1996)

(1) - Paramètre(s) atmosphérique(s) modifié(s)
(2) - Elément(s) du milieu impacté(s)
(3) - Type(s) d'aléa impacté(s)
(3) - Sous-type(s) d'aléa
Snow precipitation Snow cover Avalanches  

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Swiss Alps Eastern Switzerland Davos-Weissfluhjoch area     1896-1993 for climatic conditions
1947-1993 for avalanche events

(1) - Modifications des paramètres atmosphériques
Reconstitutions  
Observations
The greatest snowfall period during 3 days and the total amount of daily new snow during the whole winter remain stable, but show extreme variability from year to year.
The mean winter temperature in Davos was about 0.8°C higher during the past 20 years compared to the mean from 1931-1993. Significant seasonal differences can be found. The months November-December were about 0.9°C warmer, January-February were about 1.4°C warmer, but with a high year to year variability, and, interestingly, March-April showed no increase in temperature.
Modélisations
  
Hypothèses
  

Informations complémentaires (données utilisées, méthode, scénarios, etc.)

The winter climate was primarily investigated at Davos. A 96 year continuous time series with daily data from the Swiss Meteorological Institute and unpublished snow records from the SLF. To characterize each winters snow conditions the maximum snow depth, the duration of the snow coverage, the greatest snowfall period during 3 days and the total amount of daily new snow during the entire winter has been plotted.


(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions  
Observations
The snow depth shows a great short-term variability and a marked long-term fluctuation. The low values from 1925-1934 are obvious. This period is not correlated with high winter temperatures, in contrast to the low values around 1990. The snow coverage (number of days with more than 20cm of snow) shows a similar pattern to the snow depth. The variability is rather small at the begining of the century and increases afterwards.
Modélisations
  
Hypothèses
  

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
   

(3) - Effets du changement climatique sur l'aléa
Reconstitutions  
Observations
The occurrence of destructive snow avalanches in Switzerland between 1947-1993 shows no obvious trend. The situation in the surroundings of Davos shows a similar feature. However, the magnitude of the large events decrease systematically. This can be explained by the defence structures.
Modélisations
If both the snow depth and the 3-day new snow exceed 75 cm, the probability of a disastrous avalanche day increase significantly. There is strong evidence that the mean potential avalanche activity (PAA), at least for the Davos area, has remained the same for the past 96 years (1896-1993). Periods of more or less intensive PAA could be detected, but they show no systematic trend or periodicity.
Hypothèses
  

Paramètre de l'aléa
Sensibilité du paramètres de l'aléa à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Potental Avalanche Activity Snow depth and 3-day new snow

For the Davos-Weissfluhjoch area, systematic avalanche records of 50 winters have been studied. Only destructive avalanches were taken into account because they are the only information available in a fairly systematic manner.

To infer the avalanche activity before 1947, the avalanche activity was modelled using meteorological data. The correlation of meteorological factors with destructive avalanches was used to find a threshold value where numerous destructive avalanches occur. Changes in the intensity and occurrence of meteorological factors could then be used to infer the potential avalanche activity.

(4) - Remarques générales

Destructive avalanches are usually the result of extreme weather conditions. Avalanches are not primarily a meteorological phenomenon, but their occurrence is mainly dependent on the stability of the snow cover, which is strongly influenced by the weather situation. Direct correlation of long-term, daily meteorological data to avalanches events is the only feasible method to reach a significant improvement. General circulation patterns have shown promising connections to large avalanche events. Changes in these circulation patterns may therefore serve as an indicator for a changed avalanche activity.

(5) - Syntèses et préconisations