Pôle Alpin Risques Naturels (PARN) Alpes–Climat–Risques Avec le soutien de la Région Rhône-Alpes (2007-2014)
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Fiche bibliographique

Réf. Valt & Cianfarra 2010 - A

Référence bibliographique
VALT, M., CIANFARRA, P. 2010. Recent snow cover variability in the Italian Alps. Cold Regions Science and Technology, Vol. 64-2, 146–157. [Etude en ligne]

Abstract: The historical record of snow duration (from 1950 to 2009) and of snowfall (from 1960 to 2009) collected in the Italian Alps are presented and analysed. A reduction of the snow cover duration and of the snowfall stronger in springtime was detected during the last 40 years with the greatest decreasing rate during the 1990s. The last decade is characterised by a recovery from the documented decreasing trend mainly evident between 800 m and 1500 m. Principal component trend analysis of the snow duration and of the snowfall showed a long term decreasing trend. The change point test showed the existence of breakpoints between 1984 and 1994 that characterise the snow duration and snowfall time series analysed by elevation range and by seasons. These breakpoints mark a drastic trend variability in the time series: a positive trend characterises the time series before the breakpoint and a decreasing trend characterises the historical record after the breakpoint. The described negative trends result from the documented decrease in winter and spring precipitation. This in turn may either relate to a change in fraction of liquid to solid precipitation, and/or be associated to an increase of the temperatures. Northern Hemisphere and Italian Alps snow cover trends strongly correlate in the frequency domain. Among the dominant frequencies the 11.2 period was detected that may relate to the 11-year solar activity cycle.

Mots-clés

Snow cover variation - Trend analysis - Climate change


Organismes / Contact

• AINEVA, Trento (Italy), ARPAV Centro Valanghe di Arabba,BL, Italy
• Università degli Studi Roma Tre, Dipartimento di Scienze Geologiche, Roma, Italy


(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
           

(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
 
Modélisations
 
Hypothèses
 

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

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

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

(4) - Remarques générales
 

(5) - Syntèses et préconisations
Discussions and conclusions

Snow cover duration for the period 1950–2009 and cumulated snowfall for the period 1960–2009 was analysed to investigate the recent snow cover variability in the Italian Alps.

A significant linear correlation exists in the frequency domain between Northern Hemisphere snow cover extension and Italian Alps snow duration. Among the dominant frequencies the 11.2 year period was detected, possibly related to the 11-year solar activity cycle with its variability in solar radiation.

A reduction of the snow cover duration stronger in spring and between 800 and 1500 m a.s.l. was detected during the last 40 years with the greatest decreasing rate during the 1990s. This result is in agreement with findings by Valt et al. (2008) who documented a rise from 1500 to 1800 m a.s.l of the limit for reliable skiing in the eastern part of the Italian Alps. During the last decade there was a recovery of the reduction of snow cover both in winter and spring time and mainly evident at the lower elevations. A decrease of snow precipitation since the 1970s was found with a stronger rate in spring season with the greatest reduction in the 1990s. This implies a reduction of the water resources from the snow cover melting for irrigation, distribution for civil use and power production. A modest recovery in the decreasing rate of snow precipitation, mainly evident in winter between 800 and 1500 ma.s.l., characterises the last decade.

Principal component trend analysis of the snow cover duration (since 1950) and of the cumulated snowfall (since 1960) showed a long term negative trend. The change point test showed the existence of breakpoints between 1984 and 1994 that characterise both the snow duration and cumulated snowfall time series analysed by elevation range and by season. The detected breakpoints mark a drastic trend variability in the analysed time series. Specifically, according to the least-square method and Mann–Kendall test for trend, a decreasing trend characterised the period after the breakpoint. This was observed for the entire winter season and for the spring months and for the studied elevation range. However, no statistically significant trends (pN0.1) were found for the spring time series after the detected breakpoint (with the exception of the positive trend found at the cumulated snowfall principal component time series between 800 and 1500 ma.s.l. in spring time). The positive trend before the breakpoint may relate to the long snow duration and heavy snowfall regime that characterises the 1961–1990 reference period. The negative trend found after the breakpoint results from the documented decrease in winter and spring precipitation. This in turn may either relate to a change in the fraction of liquid to solid precipitation, and/or be associated to an increase of the air temperatures. At present, historical temperature records are not available for the Italian Alps although big efforts are in progress to collect a homogenous temperature record from the different Italian institution. Chiaudani (2008) showed an increase of the rainfall to the detriment of snowfall in the eastern part of the Italian Alps. However, we suppose that the maximum spring temperature increase in the eastern part of the Italian Alps reported by Chiaudani (2008) plays a significant role on the documented snow cover decreasing trends. In fact time series from stations higher than 2000 m show a modest decreasing trend for the cumulated snowfall and no trend for the snow duration (see Figs. 2–5). The moderate recovery in the decreasing trend of snow cover duration and snow precipitation observed in the last decade might be related to similar trends predicted by climate models at the global scale (Keenlyside et al., 2008). The strong correlation between Northern Hemisphere and Italian Alps snow datasets confirms the regional influence on snow cover variability. Therefore, monitoring snow cover variability is of great interest for understanding the climate change in the alpine regions as well as at the global scale.

Références citées :

 


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