Réf. Appenzeller & al. 2008 - A

Référence bibliographique complète

APPENZELLER, C., BEGERT, M., ZENKLUSEN, E., SCHERRER, S. 2008. Monitoring climate at Jungfraujoch in the high Swiss Alpine region. Science of the Total Environment, 391, 262-268. [Etude en ligne]

Abstract: A homogenized temperature record measured at Jungfraujoch, the highest permanently manned meteorological station in Europe at 3580 m asl, is presented based on almost 70 years of record (1937–2005). The observed decadal variability as well as the overall trend (1.8 °C/69 years) in the homogenized data is comparable to other homogenized Swiss time series at other altitudes. A detailed analysis of seasonal mean temperature trends revealed no significant height dependence for the period 1961–2005. The dominant trend features are the weaker trends in autumn, significant only at low altitudes. Temperature indices such as thawing days, derived from newly homogenized minimum temperature series, exhibit strong vertical and seasonal trend dependence. Strongest relative trends occur in winter at an altitude around 1000 and 1600 m asl. For the summer season relative trends in thawing days are strongest at the highest stations, as expected. At Jungfraujoch an increase of about 50% is observed for the period 1961–2005 even when the extraordinary warm summer of 2003 is excluded.

Mots-clés

Jungfraujoch - Temperature - Homogeneity - Trends - Thawing - Alpine region

 

Organismes / Contact

 

(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

Alpes bernoises (cantons de Berne et du Valais)

 Jungfraujoch

 

 3580 m

 1937–2005

 

(1) - Modifications des paramètres atmosphériques

Reconstitutions

 

Observations

Decadal variability in mean temperature: The evolution of annual mean temperature at Jungfraujoch is shown for the period 1937 to 2005 expressed as yearly anomalies relative to 1961 to 1990. The main characteristics of the curve are the warm period in the late 1940s and the shift towards warmer temperatures in the second part of the 1980s (Bader and Bantle, 2004). The anomalies reveal an increase of 1.8 °C within the 69 year period. Overall, the decadal variability at the Jungfraujoch is similar to the mean temperature evolution in Switzerland. The Jungfraujoch anomalies was compared to the annual and seasonal mean Swiss temperature record described in Begert et al. (2005), which consists of 12 homogenized series representing one of the climatic regions of Switzerland each. A remarkable uniform course of both the annual and seasonal curves is observed.

Vertical distribution of changes in mean temperature: When comparing Jungfraujoch measurements with those of other stations it becomes evident that the mean temperature evolution shows no distinct altitude dependence in Switzerland. The annual trends of mean annual 2 m temperature for 45 homogenized stations at different altitudes for the period 1961–2005 are statistically significant on the 5% level for all stations. There is no obvious dependence of the trends with altitude or geographical position.

Relative trends expressed as deviation to the mean Swiss trend indicate slightly weaker trends at high altitudes and slightly stronger trends in the lowlands. This is in opposition to the height dependence suggested for several mountain regions in Diaz and Bradley (1997). The number of stations included in their analysis was very low in Western Europe. The height dependence found [here] is weak and in the order of 15% only. These results are in agreement with other studies which also find no strong relationship between trend magnitudes and elevation using data from many places around the world (e.g. Pepin and Seidel, 2005).

Seasonal analysis shows the trends for winter (DJF), spring (MAM), summer (JJA) and autumn (SON). Again, there is no clear height dependence visible, except for autumn. More pronounced are the trend differences with season. In winter, spring and summer statistically significant increasing trends are found for all stations, except one, Samedan. This inconsistency is most likely a remaining problem in the homogenization which is doubtful for this station and could therefore lead to wrong interpretations. In autumn trends are positive as well, but statistically significant only at low altitude stations. The weaker trends in autumn are not specific for Switzerland but also found over most regions of Europe (cf. Klein Tank et al., 2005). Without including the most recent years (2003, 2004 and 2005) autumn trends were completely absent (e.g. Scherrer, 2006). The reason for the weaker trends in autumn particularly at higher altitude is not explored in detail. It could be simply a peculiarity of decadal variability. A closer investigation of the relation between local temperature, large-scale climate variability (e.g. in terms of atmospheric blocking), the occurrence of “cold-pools” over the Swiss plateau and/or Föhn situation could be a promising approach to determine whether the missing autumn trends are due to compensating natural variability or not.

Vertical distribution of changes in temperature related indices: The impact of recent warming at high and low altitudes can strongly differ. As an example the number of days per year with minimum temperature above 0 °C (Tn > 0, referred to as “thawing days”) at the Jungfraujoch were derived from a set of newly homogenized minimum temperature series of Switzerland (Begert et al., 2003) for the period between 1961 and 2005. The most striking feature is the extraordinary warm summer of 2003, where the number of thawing days has doubled. But even without the year 2003 a logistic trend estimate in annual count reveals an increase of about 50%.

Comparing relative trends in count of thawing days at different altitudes for the period 1961–2005 shows a strong dependence on height and season as expected. Annual thawing days clearly demonstrate an overall positive trend. Absolute trend values have roughly the same magnitude; however relative trend values are larger at higher altitudes than in the lowlands. All annual trends are significant on the 5% level. […] The height dependence of the logistic trends in number of thawing days for the four seasons are separately shown. Strong positive trends in thawing days occur in winter, with largest trend values at a height level between 1000 and 1600 m asl. The strongest trend is observed at Davos (1590 m asl) with an increase of more than 260% in winter. In spring and autumn, trends are less extreme but still predominantly positive. Strongest relative increases occur at heights between 1500 and 2500 m asl and in inner Alpine regions. The (insignificantly) negative autumn trends at some high altitude stations agree well with the insignificant mean temperature trends in autumn. In the summer season strongest trends in thawing days are observed at the highest Alpine stations with the strongest increase (66%) at Jungfraujoch at 3580 m asl.

Modélisations

 

Hypothèses

 

 

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

 In Switzerland a high density near surface measurement network (SwissMetNet, Frei, 2003) provides long term observations at altitudes ranging from 197 to 3580 m asl. The later altitude is the one of the station at Jungfraujoch operated by the Federal Office of Meteorology and Climatology MeteoSwiss. It is the highest permanently manned meteorological station in Europe. Measurements have been carried out since 1922 when the access by railroad was completed and the Jungfraujoch Commission was founded. Today, long term data series of Jungfraujoch and other stations on such altitudes are of great value to address questions of the current global change debate.

In this paper, the results of the homogeneity assessment of the temperature record at Jungfraujoch are examined and compared with decadal variability and seasonal trend with other homogenized Swiss time series. The observed vertical and seasonal dependence of the mean annual and seasonal temperature and derived temperature indices are discussed.

 

(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

 

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

Studies quantifying and exploring the impact of a changing climate on the high Alpine region strongly rely on stations like the one at Jungfraujoch. High altitude stations are and will remain an important part of the climate monitoring system in Switzerland and Europe.

Since 1925 meteorological measurements have been carried out at Jungfraujoch and the homogenized record of mean temperature over the period 1937–2005 shows an increase of 1.8 °C, which is comparable to the mean temperature evolution in Switzerland.

The trends in annual mean temperature for 45 Swiss stations at different altitudes for the period 1961–2005 are strongly positive and highly significant. No significant height dependence of monthly mean temperature trends was found for both, annual and seasonal values. Seasonal temperatures in winter, spring and summer are all clearly increasing. Weaker trends are found for autumn where they are statistically significant only at low altitude stations.

Non-linear dependent parameters such as thawing days show that the impact of the recent warming at high and low altitudes can strongly differ. Annual trends in thawing days for 45 Swiss stations are all positive and mostly significant. Seasonal values show that the strongest trends in thawing days are observed in winter. Remarkable changes of the height levels of the maximum seasonal trends can be observed. The strongest trends in winter occur in heights between 1000 and 1600 m asl, unlike in summer when the trend maxima rise up into the highest Alpine regions to 3500 m asl. In spring and autumn thawing days trends are strongest at an intermediate level around 1500 to 2500 m asl.

Regional climate models indicate that towards the end of the 21st century about every second summer could be as warm as 2003 (see e.g. Schär et al., 2004 and reference therein). Hence it can be expected that the observed increase in number of thawing days in the intermediate and higher Alpine region will continue.

Références citées :

Bader S, Bantle H. Das Schweizer Klima im Trend: Temperatur- und Niederschlagsentwicklung 1864–2001 (in german). Veröffentlichungen der MeteoSchweiz, Nr. 68, 48pp, 2004. Available online via http://www.meteoschweiz.ch.

Begert M, Seiz G, Schlegel T, Musa M, Baudraz G, Moesch M. Homogenisierung von Klimamessreihen der Schweiz und Bestimmung der Normwerte 1961–1990 (in german). Veröffentlichungen der MeteoSchweiz, Nr. 67, 170pp, 2003. Available online via http://www.meteoschweiz.ch.

Begert M., T. Schlegel, W. Kirchhofer, Homogeneous temperature and precipitation series of Switzerland from 1864 to 2000. Int J Climatol, 23 (2005), pp. 65–80.

Diaz HF, Bradley RS. Temperature variations during the last century at high elevation sites. Clim Change 1997; 36:253–79.

Frei T. Designing meteorological networks for Switzerland according to user requirements. Meteorol Appl 2003;10:313–7.

Klein Tank AMG, Können GP, Selten FM. Signals of anthropogenic influence on European warming as seen in the trend patterns of daily temperature variance. Int J Climatol 2005;25:1–16.

Pepin NC, Seidel DJ. A global comparison of surface and free-air temperatures at high elevations. J Geophys Res-Atmos 2005;110:D03104

Schär C, Vidale PL, Lüthi D, Frei C, Haeberli C, Liniger MA, Appenzeller C. The role of increasing temperature variability in European summer heatwaves. Nature 2004;427:332–6.

Scherrer SC. Interannual climate variability in the European and Alpine region. PhD Thesis No. 16338, Eidgenössisch Technische Hochschule (ETH), Zürich, 2006, 120pp (electronic version available at http://e-collection.ethbib.ethz.ch/show?type=diss&nr=16338).