Réf. Bader et Kunz 2000g - 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
Permafrost, climate change, evolution, modelling.

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 ", Haeberli, Kaab et al, 1998.
"Auswirkungen von Klimaänderungen auf die Gletscher und deren Vorfelder", Maisch, Wipf et al, 1998.
"Stabilité des terrains meubles en zone de pergélisol et changements climatiques - Deux études de cas en Valais : le Ritigraben (Mattertal) et la moraine du Dolent (Val Ferret)", Lugon et Monbaron, 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
  Permafrost    

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Switzerland Alps 33 glacier region classified by mountain groups in the Swiss Alps      

(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
Gradual melting and retreat of the Alpine permafrost to higher altitudes have already taken place since the end of the Little Ice Age. Thus it is estimated that the lower limit of permafrost has risen 150 to 250 m during the last 100 years.

Permafrost degradation produces a thermokast landscape in which the ground contains depressions fromed by melting of lens-shaped pieces of dead ice.
Modélisations
Reaction of permafrost to temperature with increasing depth:
(a): marked heating was observed in the first 80 m below the surface;
(b): considearble change in temperature profiles to a depth of 40 m;
(c): heating of between 0.5°C and 4°C in the top 100 m.
Using simulations,  the probable zones of permafrost were reduced by 10% from 1850 to 1990 and will decline by a further 70% by 2100.
Hypothèses
Three possible types of reaction have been distingished since the mid-19th century:
Immediate response of the permafrost to climate change in a space of years, with an increase in the thickness of the soil affected by the freeze-thaw cycle, together with subsidence and slope-type mudflow in many cases.
Disturbance of temperature profiles deep inside the permafrost over the couse of years or even decades, with new temperature gradient being established.
Very gradual rising of the lower limit of permafrost over decades, centuries or even thousands of years. The process leads to final meltdown of the permafrost.

A 1-2°C temperature rise by the middle of the 21th century would shift the lower limit of permafrost upwards by 200-700 m.

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Presence of permafrost depending on: Insolation, altitude, air temperature, snow cover. The presence of permafrost is also affected by wind changing the depth of the snow cover) and the shadow cast by the slopes. The most imporant factor in the formation and preservation of permafrost is the thermal balance at the interface between top ground layer and the atmosphere. Thus, the amount of frozen ground depends on mean annual temperature and air humidity. The position of the mean -1°C/-2°C isotherm is the lower limit of the permafrost by altitude; its upward limit is formed by the eternal snow.
The reaction of permafrost to temperature with increasing depth to global heating at ground level was simulated using single-dimension thermal balance equations. The modeling was applied to the last 100 years (a), the years 1980-1990 (b) and the IPCC scenarios A, B, C and D (c).

(3) - Effets du changement climatique sur l'aléa
Reconstitutions
 
Observations
 
Modélisations
 
Hypothèses
 

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

(4) - Remarques générales
The retreat of periglacial areas is alreday a problem for costructions at high altitude: anchors of avalanche barriers have been destabilized, thermal conditions have changed in the permafrost around building in mountain resorts, and cable-car pylons and masts for ski tows have been loosened (e.g Grächen-Seethalorn, Andermatt-Gemsstock).

(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