Réf. Beniston & al. 2003b - A

Référence bibliographique complète
BENISTON, M., KELLER, F., & GOYETTE, S. Snow pack in the Swiss Alps under changing climatic conditions: an empirical aproach for climate impact studies. Theorical and Applied Climatolgy,  2003, Volume 74, p19-31.

Mots-clés
Snow cover duration, snow cover height, type of winters, empirical approach, observation data

Organismes / Contacts
University of Fribourg, Department of Geosciences. 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, precipitation Snow pack    

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Switzerland Jura mountains, Swiss Plateau, Alps, Southern Alps. 18 meteorological stations representative of Swiss climate   317m asl to 2500m asl 1931-2000 (some stations propose data since 1901).

(1) - Modifications des paramètres atmosphériques
Reconstitutions
 
Observations

The warming rates are all significant and range from 1.8°C/century in Neuchâtel to 3.5°C/century in Säntis. The general rise of winter minimum temperatures began in the early to mid-1960s at all sites, and underwent a cooling in the early to mid- 1980s before warming rapidly since.

The precipitation rates are much more difficult to asses with strong statistical noises, even when smoothed trough a 5 years filter. The only significant variations has been observed at the Säntis high elevation site with a 3.3 mm/day increase (1961-1990 as reference period) and corresponds to almost twice the average value. There are increasing trends of solid precipitation at high elevations, and increasing trends of liquid precipitations at low to medium elevations.

Milder winters are associated with high precipitations levels than cold winters, but with more solid precipitations at elevations exceeding 1,700 – 2,000 m above sea-level, and more liquid precipitations below.

Modélisations
 
Hypothèses
 

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

Data issued by MeteoSwiss; some raw data should be taken with caution because some observation sites changed (shift of the Davos site in the 1970's) or because of local conditions (Säntis is located on a mountain summit). The sites located in the southern slopes have been considered because of the strong mediterranean influences on these area.

The temperature anomalies as a function of time have been analysed with the 1961-1990 period as reference and the use of a 5 years filter to remove the noisiness of interannual variability. The same analysis has been conducted for the precipitations.


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

At the low elevation site of Château d'Oex, the snow depth is reduced by 45% between the 1960s and the 1990s. But there is a high interannual variability, e.g. the duration ranged from 10 days during the 1961-1962 winter to 110 days the next winter. During the same time interval, the Davos site experienced a loss of 12% of the snow depth (reduction of average total accumulation from 330cm to 288cm). These trends are inversed at the high elevation site of Säntis with an enhancement of snow depth of 35% (increase from 1590 cm for the 1960's to 2475 cm for the 1990s).

On the overall, the length of the snow season tended to decrease at most location since the early 1970's.

Since the mid 1980's and up till today, the lenght of the snow season and the snow amount at Arosa, based on a 20 cm treshold, have been reduced by 2-3 weeks as a result of unusually high and persistent pressure over the Alps. This shift remains within the ± 2 weeks (duration occurs between end of November toward mid-May). The situation of today is similar to the situation in the early 1930's.

There is a strong linear relation between snow duration and snow height for the 18 stations studied (r = 0.97).

Large scale forcing, rather than just local or regional factors, plays a dominant role in controling the timing and amount of snow in the Alps. The study suggests a strong domination of the temperature on snow duration. Small shifts of winter mean minimum temperature may lead to substantial change in the lenght of the snow cover season.

Modélisations
 
Hypothèses
 

Sensibilité du milieu à des paramètres climatiques
Informations complémentaires (données utilisées, méthode, scénarios, etc.)
The relative constancy of the beginning and end of the snow season (within more or less two weeks) is principally linked to the cycle of direct solar energy.
Monthly representation of the quantities of snow over a long period (1949-2000) at the Arosa site through a Hövmöller-type diagram.

(3) - Impacts 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

 


(5) - Syntèses et préconisations