Réf. Beniston & Stephenson 2004 - A

Référence bibliographique complète
BENISTON, M and D.STEPHENSON. Extrem climatic events and their evolution under changing climatic conditions. Global and Planetary Change, 2004, vol 44, p 1-9. 

Abstract: This short introductory paper illustrates some key issues concerning extremes by focusing on daily temperature extremes defined using quantiles and threshold exceedances. The examples include both a low- and a high-elevation site in the Swiss Alps where long records of homogenous daily data are readily available. The analysis of extremes highlights several features, some of them taken from the 2003 heat wave that affected Europe, in particular significant changes in the trends of quantiles in the course of the 20th century, differences in the altitudinal behavior of maximum or minimum temperatures, and close links between means and the extreme quantiles of daily temperatures.


Extreme events, daily temperature extreme, 2003 summer, heatwave.

Organismes / Contacts

Department of Geosciences, University of Fribourg / Department of Meteorology, Universiy of Reading. Martin.Beniston@unige.ch

(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
Temperature Permafrost
Mass movement
Rock falls and mudslides

Pays / Zone
Massif / Secteur
Site(s) d'étude
Période(s) d'observation
Switzerland Alps Basel and Säntis   Basel (367 m asl) ; Säntis (2500 m asl) 1901-2000

(1) - Modifications des paramètres atmosphériques

The observed temperature extrems exhibit contrats between the hot and cold seasons, as well as between high and low elevation sites. In addition to the interannual variability, long term upward trends are also apparent in the both sites series. The "fingerprint" of the long positive phase of the North Atlantic Oscillation (NAO), whose influence on climate on both sides of the Atlantic is dominant in winter (Wanner et al., 2001), can be discerned in the winter Tmin time-series from the late 1970s onwards.

All the temperature trends are positive and are fluctuating between 0.5°C and 2.2°C per century for the period 1901-2000. Some of these trends seems to accelerate in the recent years (e.g., the trends in minimum winter temperature). The trend at the colder high-latitude station (Saentis) are larger than those at the low-altitude station (Basel). The trends at the low-elevation site are the largest during the winter time. All the trends at these local values are greater than the global mean value of + 0.6°C.


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

Use of temperatures data for the both studied sites and calculation of the 10%, 25%, 50%, 75% and 90% quantiles.

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

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

(2) - Effets du changement climatique sur le milieu naturel
Many damaging natural hazards can occur in the absence of an intense or rare climate event that actually triggers the hazard. The mountain permafrost degradation exemple is relevent: the degradation of permafrost, whereby a rise of atmospheric temperatures beyond a certain threshold that would not on itself constitutes a temperature extreme (according to the IPCC definition), can melt the permafrost to a sufficient degree for a significant reduction of the cohesion of mountain substrata to occur, thus enhancing the potential for rock and mud slides.

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 general treshold above which an extrem event could occur is really difficult to estimate because of the local paticularities of each site. A treshold at low-elevation site can not be used for high elevation site, and differences in latitude have to be taken into account for treshold estimations. For example, the threshold above which a heat wave may occur can be arbitrarily set at 30°C, which is typically a level that is exceeded at low elevations in Switzerland a few days each year. At higher elevations, above 1000 m or higher, the likelihood of encountering temperatures above 30°C is negligible under current climate. The temperature threshold for cold spells poses similar problems for different altitudes, because what might be a normal winter temperature at 3000 m above sea level becomes a rigorous cold spell in the lowlands.

(5) - Syntèses et préconisations

Références citées :

WANNER, H., BROEINNIMANN, S., CASTY, C., GYALISTRAS, D., LUTERBACHER, J., SCHMUTZ, C., STEPHENSON, D.B., XOPLAKI, E., 2001. North Atlantic Oscillation—concepts and studies. Surv. Geophys. vol. 22, 321–381.