Réf. Bader et Kunz 2000a - R: PNR 31

Référence bibliographique complète
Climate Risks - The Challenge for Alpine Region - PNR31. / ed. by BADER S., KUNZ P. Zürich : vdf Hochschuverlag AG an der ETH Zürich, 2000, 291 p.

Mots-clés
Past avalanche activity, meteorological conditions, past trends, possible evolution.

Organismes / Contact
Partenaires
NRP 31 Programme Leaders
Thunstrasse 91, CH-3006 Berne
Tel. : +41 31 356 65 65
Fonds National Suisse; Swiss Re; Office Fédéral de l'Environnement, des Forêts et du Paysage; Direction du Développement et de la Coopération; ProClim; CLIRIS Recherche sur les Risques Climatiques; Hochschulverlag an der ETH Zürich

Principaux rapports scientifiques sur lesquels s'est appuyé le rapport
Wechselwirkungen zwischen Klima, Lawinen und technischen Massnahmen", Schneebeli et al, 1997.
"Raum-zeitliche Rekonstruktionen von Witterungsanomalien und Naturkatastrophen 1496-1995", Pfister et al, 1997.

(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
    Avalanches  

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Switzerland Swiss Alps Davos, Bever and Andermatt     1881-2000

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
No significant statistical trend or periodicity for the parameters analysed during the 20th century. No marked change in the distribution of extreme snowfall events.
Modélisations
 
Hypothèses
 

Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Day by day parameter (temperature, precipitations, cloud cover, wind direction and force, new snow (snow falling for 3 days), height and duration of snow cover) for three meteorological stations: Davos (meteorologic data avalaible from 1881 / snow cover data from 1896); Bever (1901/1910) and Andermatt (1901/1941).

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
No significant statistical trend or periodicity for the height and duration of snow cover during the 20th century.
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
During the past three centuries, periods of high avalanche activity have generally coincided with cold, damp winters. High-intensity events occur at very irregular intervals, with an average of occurence of 1 event / 2.5 years for the 1947-1993 period. Events of high to disastrous intensity occur at much longer intervals, several decade or even a whole century.

No marked change in the avalanche situation in the northern Alps over the 1881-1992 period. Slight general increase of the avalanche situation in the southern Alps since 1945.No general trend in avalanche activity (increase or reduction) can be found in the data relating to major events since the 15th century or systematic surveys of destructive avalanches in the past 50 years.

The climate has not change enough during the 20th century to produce any palpable effects on avalanche activity.
Modélisations
 
Hypothèses
A rise in winter temperature with a consequent shortening of the period of snow cover will probably have the effect of shortening the season when avalanches take place. Early moistering of the snow cover as a result of a warmer atmosphere will indeed create avalanche of heavy or wet snow. Taken over the whole year, there should be the same number of destructive avalanche events involving heavy snow.

Considered as an average and ignoring any fluctuations, a slight climate change will not affect avalanche activity fundamentally. A 1-2°C variation and a 10-20% variation in precipitation will not influence the occurence of extreme meteorological conditions leading to avalanche. Unlike glaciers, avalanche react more to sudden extreme fluctuations than to long-term climate change. Hence they cannot be used as indicators of climate change during the past centuries.

Paramètre de l'aléa
Sensibilité du paramètres de l'aléa à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Avalanche activity Temperature, precipitations, cloud cover, wind direction and force, new snow, height and duration of snow cover
The data on avalanche activity may be divided into 3 periods:
prior to 1887: descriptions often accompanied by simple meteorological data. The informations comes from records and articles covering the whole Switzerland.
1888-1946: the quality of systematic meteorological data improves, though observations of avalanche activity are still descriptive, sporadic and inadequately documented.
post 1947: avalanche activity is systematically compiled and archieved for the whole area of the swiss Alps, so statistical comparison with meteorological parameters is now possible.

The data on avalanche activity have been compared with meteorological data.

(4) - Remarques générales
 

(5) - Préconisations et recomandations
Destinataires et portée du rapport Policy makers, swiss citizens, teachers and students in the climatic and environmental studies
Types de recommandations et / ou préconisations The effect of phycisal measures and appropriate planning of residenial zones is certainly greater than that of any change in avalanche activity which may result from climate change.