Réf. Bader et Kunz 2000e - 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
Precipitation, mass movement, activity, reaction to changing climatic conditions.

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
"Grands glissements de versants et climat, VERSINCLIM - Comportements passés, présents et futurs des grands versants instables subactifs en fonction de l'évolution climatique, et évolution des mouvements en profondeur", Noverraz, Bonnard et al, 1998.
"Instabilités de pente en terrain de flych et changements climatiques", Lateltin, Beer et al, 1998.
"Pentes instables dans le Pennique valaisan : une méthodologie d'auscultation des falaises", Rouiller, Jaboyedoff et al, 1998.  

(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
Precipitation   Mass movements  

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Switzerland Alps and PreAlpine region        

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
The rain which fell in the last 20 years tended to be concentrated on the cold season. Precipitation has increased by an average of 15-30% over the previous annual norm in Western Switzerland and to a lesser extent in Ticino.
Modélisations
 
Hypothèses
 

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

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
 
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
Most of the landslides, including the Alpine ones, result from decompression of the valley sides following the glacier retreat.

Climatic parameters such as temperature and sunshine play a relatively minor part in reactivating movements, at least outside the permafrost areas. Precipitation has more influence, although the situation is not clear. There is no simple correlative relationship between precipitation volume data and mass movements.

The rain which fell in the last 20 years tended to be concentrated on the cold season, the time when it is more effective in destabilizing landslides. The 15-30% increase in the last 20 years precipitations in Western Switzerland has resulted in intensification and reactivation of land movements of all kinds (usually in connection with large landslides). In the Eastern Switzerland, the event due to instability are in form of slope-type mudflows rather than large mountainside landslides caused by more constant precipitation.

Reactivation of movements in the flysch areas has been experienced much more in the western than in central Switzerland since 1978.
Modélisations
 
Hypothèses
A significant and marking change in annual precipitation and in the seasonal distribution of rain may have very marked effects on landslide activity.

An increase in the minimum temperature and precipitation during winter and spring may lead to a general increase in displacement speeds in unstable flysch areas (PreAlpine region) and reactivation of small lanslides (<1km²) at low altitude (<1500 m asl). Rain falling on the frequently unfrozen ground can seep into it more easily, thus reinforcing the factors which trigger landslides. Hence, the period of effective seepage of rain can be extended (by 30-50 days). Re-filling of ground water tables in landslide areas is therefore dependant on the position of the 0°C isotherm in winter.

This may lead to significant reactivation of old, latent landslides or potentially instable regions in the spring. Some unstable zone moving at low intensity (cm/year) may be moving at medium intensity (dm/year).

Paramètre de l'aléa
Sensibilité du paramètres de l'aléa à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
 
 

(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