Réf. Bader et Kunz 2000b - 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.

Flooding events, historical analysis.

Organismes / Contact
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
"Auswirkungen von klimlatischen Variationen auf Wasserhaushalt und Abfuss im Flussgebiet des Rheins", Gurtz, Baltensweiller et al, 1977.
"Influence des changements climatiques sur le régime hdrologique et hydraulique des cours d'eau", Overney, Consuegra et al, 1997.
"Raum-zeitliche Rekonstruktion von Witterungsanomalien une Naturkatastrophen 1496-1995", Pfister, 1998.
"Analyse der räumlichen une zeitlichen Variabilität der Hochwasser in der Schweiz", Weingartner, Aebischer 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

Pays / Zone
Massif / Secteur
Site(s) d'étude
Période(s) d'observation
Switzerland Swiss Alps Focus on Valais, Uri, Ticino and Graubünden cantons and on Lago Maggiore     1500-2000

(1) - Modifications des paramètres atmosphériques

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

(2) - Effets du changement climatique sur le milieu naturel

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

(3) - Effets du changement climatique sur l'aléa
During the last 500 years, on the Alpine region, there have been two periods with very little flooding: 1641-1706 and 1927-1975, and two periods with a great deal of flooding: 1550-1580 and 1827-1875. Such inventories are based on "report of damage" and may not reflect the tendency for the event itself.

During the 1641-1706, the whole Alpine region was spared any serious flooding; even Lago Maggiore did not overflow its banks. Considering the similarity of results from all regions, it can be explained by a gap in the inventories but by a pause in the flooding cycle. This pause concides with the "Maunder Minimum", a period of reduced solar activity.

The period 1827-1875 is marked by a sharp increase in flooding events following a series of extremly wet autumns. Lago Maggiore overflow its banks almost every 4 years.

The decrease of flooding between 1927 and 1975 is possibly realted to the planning and protective measures undertaken.

The general tendency for the 1800-2000 period  is an annual increase in flood damage since 1800. This can very likely be explained by an increase in potential hazards. The period from 1940-1965 stands out as having a far lower number of events.

The increase in the frequency of extreme flooding in the Alpine region is still within the range of natual variability (as in the case of mountain torents) and can not be attribute solely to climate change.
Flooding events appears to be on the increase again since 1975. Extreme events such as those which affected the Alpine region in 1987 and 1993 took place towards the end of summer and in autumn. They are caused by rising bodies of moist and warm air from the South/South-West which are transported from the Mediterranean and blocked by the alpine barrier when the 0°C isotherm is very high (>3000m asl, giving many precipitation mainly in the form of rain).
It is quite impossible to draw up a precise balance sheet of flood-reducing and flood-promoting actions. However, the flood-reducing actions took full effect before 1960, whereas flood-promoting actions have tended to multiply since 1960 and are more dominant in low altitude regions. The link between flodding events and climatic parameters is often obscured by many anthropogenic factors.

Paramètre de l'aléa
Sensibilité du paramètres de l'aléa à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
Events recorded in the inventory for the last few centuries were only mentioned in terms of the damage caused to public or private property. Thus each event was represented by a "report of damage" caused by particular meteorological conditions. This described the extent of the damage and its geographical distribution.
The information was collected from accounts of past events, archives, monographs or various observations. Based on such an inventory, a database of about 4000 events, divided into different kinds of damage and covering the period 1800-1995, has been drawn up.

(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