Réf. Casty & al. 2005 - A

Référence bibliographique complète
CASTY C, WANNER H, LUTERBACHER J, ESPER J, BHOM R. Temperature and precipitation variability in the European Alps since 1500. International Journal of Climatology. 13/05/2005, 26 p.

Abstract: High-resolution temperature and precipitation variations and their seasonal extremes since 1500 are presented for the European Alps (43.25–48.25 °N and 4.25–16.25 °E). The spatial resolution of the gridded reconstruction is given by 0.5° × 0.5° and monthly (seasonal) grids are reconstructed back to 1659 (1500–1658). The reconstructions are based on a combination of long instrumental station data and documentary proxy evidence applying principal component regression analysis. Annual, winter and summer Alpine temperatures indicate a transition from cold conditions prior to 1900 to present day warmth. Very harsh winters occurred at the turn of the seventeenth century. Warm summers were recorded around 1550, during the second half of the eighteenth century and towards the end of the twentieth century. The years 1994, 2000, 2002, and particularly 2003 were the warmest since 1500. Unlike temperature, precipitation variation over the European Alps showed no significant low-frequency trend and increased uncertainty back to 1500. The years 1540, 1921 and 2003 were very likely the driest in the context of the last 500 years.

Mots-clés
Temperature and precipitation variability, 1500-2004 period, summer/winter/annual periods

Organismes / Contacts
Climatology and Meteorology, University of Bern ;
NCCR Climate, University of Bern,
Swiss Federal Research Institute WSL,
Central Institute for Meteorology and Geodynamics, Vienna.

(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      

Pays / Zone
Massif / Secteur
Site(s) d'étude
Exposition
Altitude
Période(s) d'observation
Greater Alpine Region   199 grids points from 43.25° to 48      

(1) - Modifications des paramètres atmosphériques
Reconstitutions

Warm periods are distinguished from about 1780 to 1810, 1890 to 1945, and the 1970s onward. The accumulation of positive temperature extremes during the last 10 years is remarkable. In the Alpine area, 1994, 2000, 2002 and 2003 were the warmest within the last 500 years. 1540 was the warmest year (+1.4 °C compared with the twentieth century annual Alpine mean temperature of 8 °C) and 1740 the coldest year during the reconstruction period (−2.5 °C).

The lowest temperatures were recorded during the last decades of the seventeenth century, which is in agreement with the coldest period over Europe back to 1500. Winters in the 1690s were extremely harsh in the Alpine area with temperature anomalies of −1.6 °C in agreement with independent findings of Pfister (1992, 1999). Shorter cold periods appear in the sixteenth century and around 1890. A strong transition to warm winter conditions is found from 1890 to 1915. After the 1960 winter, Alpine temperatures were above the average twentieth-century conditions. With an anomaly of −4.8 °C, 1829/1830 was the coldest Alpine winter (twentieth century winter mean temperature is 0 °C) and 1606/1607 the warmest (+3.5 °C). The uncertainties of the winter reconstruction are around 1.1 °C until 1770 and around 0.6 °C since the nineteenth century.

The variability is lower for summer than for winters. Warm summers were experienced around 1550, periodically in the seventeenth century, in the second half of the eighteenth century, from 1946 to 1950 and from 1970 onward. The summer of 2003 was by far the warmest since 1500 with a unique anomaly of around +4.4 °C compared with the summer mean temperature 1901–2000 of 16.1 °C. 1807 was the warmest Alpine summer during the reconstruction period (+2.15 °C). The absolute coldest Alpine summer was 1816 (−1.9 °C), in agreement with the findings of Pfister (1992, 1999).

Dry periods prevailed around 1860 and after 1945. In the annual precipitation time series, fast transitions from wet to dry conditions around 1830, 1920 and 1945 are recorded. The year 1540 was the absolute driest of the last 500 years (anomaly of −360 mm compared with the annual precipitation sum of around 1200 mm for the twentieth century) and 1627 the absolute wettest (anomaly of +305 mm).

Dry winters occurred in the second half of the nineteenth century, and some very dry winters between 1990 and 1994. Wet winter conditions are seen in the 1670s, 1720s, 1910s and the years 1950 to 1990. Interannual summer precipitation shows three prominent dry periods: around the 1540s, after 1770, and after 1860. Also, after 1970 a decrease in summer precipitation is found. Very wet summers occurred from 1550 to 1700. 1540 was the absolute driest summer since 1500 in the Alps (anomaly of −164 mm with regard to the twentieth century mean summer precipitation sums of 352 mm), and the summer of 2003 was of comparable magnitude. 1663 was the absolute wettest summer (+148 mm).

It is remarkable that positive winter extremes exceeding two standard deviations are observed only in the twentieth century. 1915 was the wettest Alpine winter (anomaly of +141 mm with regard to the twentieth century winter mean of 245 mm), and 1858 the driest winter (−132 mm).

Central Europe and the Alps are situated in a band of low correlations of the influence of the NAO on temperature or precipitation patterns.

The Alpine precipitation time series do not indicate significant trends. The expected increase in precipitation as a result of increased temperatures for the warm period at the end of the twentieth century (IPCC, 2001) is not revealed for the Alps.

Winter temperatures show positive correlations with the NAOI. From 1690 to 1750 (+/−15 years, due to the 31-year window), and between 1850 and 1880 Alpine temperatures are uncorrelated with the NAOI. The Alpine winter precipitation shows negative correlations with the NAOI. Again, these relations are not stable over time and not always significant. From 1675 to 1700, and around 1750, the Alpine winter precipitation is not correlated with the NAOI. Significant periods are detected from 1710 to 1740 (with a break around 1730), 1780 to 1790 and after 1860, with a distinct relapse from 1920 to 1940, that exceed the 95% confidence level. During these periods, a high (low) NAOI value caused dry (wet) Alpine climate conditions.

Observations
 
Modélisations
 
Hypothèses
 

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

Temperature and precipiation data
High-resolution reconstructions of gridded temperature and precipitation patterns for the greater European Alpine region back to 1500 using long instrumental data in combination with documentary proxy evidence, with a spatial resolution of 0.5° × 0.5° equal to 199 grid points and complement recently established tree-ring based reconstructions over the European Alps or parts of it. Eighty seven early instrumental temperature and 146 precipitation time series from all over Europe in combination with 11 documentary records for temperature (precipitation) including estimates derived from narratives, annals, scientific writings and monastery records are used as predictors for the gridded reconstruction of the greater Alpine area climate.

NAO correlation
Thirty-one-year running correlations between the extended winter (DJFM) North Atlantic Oscillation Index (NAOI; Cook et al., 2002) and the Alpine extended winter (DJFM) temperature and precipitation time series from 1659 to 2000 were computed. Prior to 1659, only seasonal (DJF) Alpine reconstructions are available.


(2) - Impacts 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) - 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.)
 
 

(5) - Syntèses et préconisations
 

Références citées :

IPCC. 2001. Climate Change 2001: The Scientific Basis., Houghton JT, Ding Y, Griggs DJ, Noguer M, van der Linden PJ, Dai X, Maskell K, Johnson CA (eds). Cambridge University Press: Cambridge, UK.

Pfister C. 1999. Wetternachhersage. Haupt: Bern.

Pfister C. 1992. Monthly temperature and precipitation in Central Europe 1525–1979: quantifying documentary evidence on weather and its effects. Climate since A.D. 1500, Bradley RS, Jones PD (eds). Routledge: London.