Réf. Bollschweiler & Stoffel 2010 - A

Référence bibliographique complète

BOLLSCHWEILER, M., STOFFEL, M. 2010. Changes and trends in debris-flow frequency since AD 1850: Results from the Swiss Alps. The Holocene, 20(6) 907–916, DOI: 10.1177/0959683610365942. [Etude en ligne]

Abstract: Although studies have repeatedly focused on feedbacks and impacts of climate change on mass movements in the past, the inter-relations between climatic variables and debris-flow occurrence remain widely unclear and ambiguous to date. Most studies on past debris-flow occurrence remained rather isolated reconstructions for single torrents or they were restricted to short time periods. It is therefore the aim of this study to provide a regional chronology of past debris-flow events for the Zermatt Valley (Swiss Alps) and to go beyond the simple dating of events. Based on tree-ring reconstructed debris-flow histories of eight torrents, [the authors] shed light on changes and trends in debris-flow occurrence, climatic conditions prevailing during events and on potential evolutions in a future climate. Based on the analysis of tree-ring records of 2467 conifers (mainly Larix deciduas and Picea abies), 417 events between AD 1600 and 2009 were assessed. Decadal frequencies suggest peaks in debris-flow activity after the end of the ‘Little Ice Age’ and for the period 1920–1929. In contrast, activity was rather low during the most recent part of the record (2000–2009), which is in concert with the observed decrease in the number of triggering rainfall events. Long-term trends in debris-flow occurrence were analysed for three time intervals of the period 1850-2009 with Student’s t-tests. For the debris-flow frequency of the entire valley, no significant trends can be observed over the last 150 years. [The authors] conclude that the occurrence of debris flows would depend on short-term changes in triggering rainfall rather than on long-term climatic changes.

Mots-clés

Climate change, Debris flow, Frequency, Swiss Alps, Tree rings, Trends

 

Organismes / Contact

• Laboratory of Dendrogeomorphology (dendrolab.ch), Institute of Geological Sciences, University of Berne, Switzerland (michelle.bollschweiler@dendrolab.ch)
• Institute for Environmental Sciences (ISE), University of Geneva, Switzerland

 

(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

Exposition

Altitude

Période(s) d'observation

Suisse

Canton du Valais

Huit torrents dans la vallée de Zermatt : Ritigraben, Grosse Grabe, Bielzug, Fallzug, Geisstriftbach, Birchbach, Dorfbach et Wildibach

Est et ouest

Cônes de déjection entre 1200 et 1800 m ; bassins versants entre 1900 et 4500 m d’altitude

1600-2009

 

(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

Major differences and trends in debris-flow activity were identified at the decadal timescale with peaks in activity toward the end of the LIA and in the early twentieth century when warm-wet conditions prevailed during summers in the Swiss Alps. [The authors] also observe a considerable decrease in frequency over the past decades which result from a decrease in the frequency of triggering precipitation events. In contrast, [they] cannot identify any significant trends in the debris-flow series between 1850 and 2009 as soon as longer-term changes (i.e. changes in 50-year segments) are addressed.

[The authors] therefore conclude that large-scale climatic conditions would not be the only limiting factor for debris-flow occurrences in the Zermatt valley but that the presence and timing of triggering events would represent a crucial element. Notably, the focus of future research should therefore be on alterations in the number, timing and intensity of rainfall events in a future greenhouse climate. Nevertheless, the specific geomorphic conditions in the source areas of debris flows should not be neglected either and we therefore suggest to integrate rock-glacier movements, grain-size distribution of debris-flow material and other sedimentological aspects into future analysis to foster the understanding of debris-flow triggering and changes in activity in Alpine catchments.

Observations

 

Modélisations

 

Hypothèses

 

 

Sensibilité du milieu à des paramètres climatiques

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

 

Based on a uniquely large spatial and temporal data set of past events obtained from tree-ring series of conifers influenced by debris-flow activity, this paper addressed past debris-flow occurrence in eight torrents of the Zermatt valley since ad 1600 and 1850. In total, 417 debris-flow events were recorded in 226 different event years between ad 1600 and 2009. Since 1850, 296 events and 134 event years are registered in the tree-ring series collected in the eight torrents.

 

(3) - Effets du changement climatique sur l'aléa

Reconstitutions

 

Observations

 

Modélisations

 

Hypothèses

 

 

Paramètre de l'aléa

Sensibilité des paramètres de l'aléa à des paramètres climatiques

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

 

 

 

 

(4) - Remarques générales

 

 

(5) - Syntèses et préconisations

 

Références citées :