Réf. Bader et Kunz 2000d - 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
Glaciers fluctuations since 1850, rise of the equilibrium line, periglacial retreat (interaction permafrost/glacier), natural hazards.

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
"Eisschwund und Naturkatastrophen im Hochgebirge", Haeberli, Kaab et al, 1998.
"Auswirkungen von Klimaänderungen auf die Gletscher und deren Vorfelder", Maisch, Wipf 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
  Glaciers, erosion Glacial hazards Glacial lake outburst flooding and ice avalanche

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Switzerland Alps 1923 glaciers all over the Swiss Alps     since 1850

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

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

(2) - Effets du changement climatique sur le milieu naturel
Reconstitutions
 
Observations
About 100 glaciers are thought to have disappeared from the Swiss Alps since they reached their maximum extent in 1850. The percentage retreat is inversely proportional to the initial area of the glacier. Glacier where the original dimension (area, lenght and volume) were small have lost proportionally more ice in their retreat than larger glaciers. The small one thus appear to be more sensitive to climate change.

In connection with the 0.5-0.7°C warming since the middle of the 19th century, the total ice-covered areas in the Swiss Alps have declined from about 1800 km2 to 1300 km2. 27% of the areas existing in 1850 have disappeared. On average, swiss glaciers have lost about 490 m (35%) of their original extent since 1850. Glaciers have also narrowed by an average of 40 m. The total volume of ice diminished by approximately one-third (107 to 74 km3). Between 1850 and 1973, the line of equilibrium rose by approximately 70 m (from 2740 to 2810 m asl).

The most impacted zone is the central and northern Graubünden region, and the less impacted zone is the bernese Alps region.

On the european scale, the retreat is still more significant: Alpine glaciers have lost about half their volume of ice and 30-40% of their original area since 1850.
Modélisations
 
Hypothèses
The + 100 m rise of the glaciers' line of equilibrium correspond to a 0.6-0.7°C warming. With a 100 m rise of the snow line (corresponding to year 2015 for IPCC scenario A or year 2025 for IPCC scenario C), a fifth of the present glaciers and a fourth of the glaciated area of the Swiss Alps will disappear, relative to the situation in 1973. In a + 200 m scenario, 847 of the 1923 existing glaciers will be left. In a +300 m scenario (timescale 2060-2130), over three-quarter of today's glaciers will already have disappeared.

The increasing slope erosion will probably accelerate in the periglacial areas and will affect various type of natural hazards: landslides, rock falls, floods, slope-type mudflows.

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Sensitivity of equilibrium of the ice masses to: air temperature, humidity, supply of winter snow (accumulation rate, depending on the ratio of rainfall to snowfall), insolation and aspect (orientation).
3 important "time windows" in the history of the glaciers provided a basis for the study: the maximum extend of the glaciers in 1850, the present situation (1973, the reference year for the swiss inventory of the glaciers), and various scenarios of glaciers retreat for the 21th century. 2244 swiss glacier units have been recorded in the CH-INVGLAZ database according to about 50 different quality and quantity parameters typical of each glacier analysed.

(3) - Effets du changement climatique sur l'aléa
Reconstitutions
 
Observations
With its below-zero temperature, the permafrost can stabilize the base and front of the glaciers. But any change in the thermal conditions in the zone of contact between the glacier and the underlying rock may then produce differential movements within the ice. (e.g the Eiger glacier in the Bernese Oberland: local internal fracturing of a tongue ice at the western fank of the Eiger may cause local breack-up of ice; at least 100 000 m3 of ice are in danger of falling onto the Eigerletscher Station of the Jungfrau station. A monitoring system has been installed since 1990).
Modélisations
 
Hypothèses
The increasing slope erosion will probably accelerate in the periglacial areas and will affect various type of natural hazards: landslides, rock falls, floods, slope-type mudflows.

A warming climate will also lead to the formation and enlargement of supra-/sub- glacial lakes resulting from retreat of the glacier snouts. Rising temperatures and heavy rainfall over glacial lakes may be expecetd to cause rapid melting of accumulated dead ice, enlargement of periglacial lakes and consequent bursting of moraine wall with a sudden emptying of sub-/peri- glacial lakes (GLOF, Glacial Lake Outburst Flooding). Global warming may moderate the temperature of the cold glaciers attached on very steep slopes and then affect their stability.

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