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- PublicationMétadonnées seulementSummer 2003 maximum and minimum daily temperatures over a 3300 m altitudinal range in the Alps(2004)The summer of 2003 was extremely hot in Western Europe and in the Alps. Here I analyse the role of elevation in the temperatures measured in 2003, and I compare daytime and nighttime values. Records from 16 stations at varying elevations show that, during the night, there was a significant correlation between heat and altitude. Hot nighttime temperatures were particularly frequent at low elevation. The frequency of unusually hot daytime highs was not correlated with altitude, but with the average degree of insolation of the sites. Compared to long-term averaged values (1961-1990) the temperatures were hottest in the normally sunniest sites. The unusual nature of the 2003 heat wave was not the absolute daily extreme values, but the lack of cool temperatures and the large number of very warm days. Averaged over all climate stations, half of the days in summer were hotter than the 90th percentile (climate normals 1961-1990), with up to 72% at some stations.
- PublicationMétadonnées seulementUse of LIDAR measurements and numerical models in air pollution research(1990)
;Beniston, Martin ;Wolf, Jean-Pierre ; ;Kölsch, H J ;Rairoux, PWöste, L
- PublicationMétadonnées seulementChanges in daily and nightly day-to-day temperature variability during the twentieth century for two stations in Switzerland(2001)An analysis of day-to-day variability was performed on two century-longs daily minimum and maximum temperature series from Switzerland. Warmer temperatures during the 20(th) century have been accompanied by a reduction in day-to-day variability, particularly for minimum temperatures and for winter. There is a significant negative correlation between day-to-day variability and the skewness of the temperature distribution, particularly in winter and for minimum temperatures. Lower variability is linked to a reduced number of cold days and nights. Higher NAO index values tend to be associated not only with warmer temperatures but also with lower day-to-day variability. This paper confirms that the temperature warming during the 20(th) century has happened mainly through the loss of the coldest part of the series, not only in the 24-hour or yearly cycle, but also through the loss of the coldest episodes in each month.
- PublicationMétadonnées seulementClimate change may already threaten Scots pine stands in the Swiss Alps(2004)
;Dobbertin, MatthiasLarge numbers of Scots pine are dying in the dry inner-alpine valleys of the European Alps; in Switzerland, locally almost half the Scots pine (Pinus sylvestris L.) population has died since 1995. As Switzerland's temperature has increased at more than twice the global average in the 20(th) stop century and as most of this increase has occurred during the last 20 years, we investigated possible relationships between the dying Scots pine and climatic parameters. We centred our studies in the upper Rhone valley. Our results show that the strong climatic warming that has occurred in recent years may well be the indirect cause of the mortality observed in these forests. Tree mortality was highest following the dry and hot year 1998, and tree defoliation, an indicator of tree vitality, showed a strong correlation with the previous year's precipitation. While precipitation showed no clear significant trend over time, the number of warm days (mean >20degreesC, maximum >25 degreesC) and potential evapotranspiration have significantly increased over the last 20 years. Higher temperatures favour pine wood nematodes and bark beetles, both of which are found at the study site, and increasing drought stress reduces tree resistance against pathogens. As these forests have in part protective functions, there is a need to better understand the mortality through interdisciplinary research and also to find means to change the species composition in order to establish tree species that are better able to withstand warmer temperatures.
- PublicationMétadonnées seulementDie Klimaveränderung bedroht die Föhrenwälder im Wallis(2006)
; ;Dobbertin, Matthias ;Rigling, Andreas ;Graf Pannatier, ElisabethWohlgemuth, Thomas
- PublicationMétadonnées seulementChangements climatiques: connaissances actuelles pour un enseignement(2013-6-3)
- PublicationMétadonnées seulementIncendies de forêts au Sud des Alpes et en Australie(2002)
;Reinhard, Michael ;Alexakis, Emanuele
- PublicationMétadonnées seulementExtreme temperature analysis under forest cover compared to an open field(2011)
;Ferrez, Jacques ;Davison, Anthony C.We analyse air temperature data from 14 sites in Switzerland, each with two weather stations in close proximity, one under a forest canopy and the other in the open. We use the statistics of extremes to investigate how extremely high maximum and extremely low minimum temperatures depend on the effect of forest cover. Our analysis shows that temperature maxima at two nearby stations are less dependent than are temperature minima. Maxima under the canopy are influenced by altitude: for higher sites, the maxima are less variable and depend less on the open-field data. Southerly orientations increase the dependence of minimum temperatures and so reduce the sheltering effect during cold periods. Extreme maximum and minimum temperatures occur less within conifer forests, indicating that the insulation provided by conifers all over the year is more efficient than that provided by deciduous species. Steepness of slopes has a complex impact on distributions of extremes and on their dependence. (C) 2011 Elsevier B.V. All rights reserved.
- PublicationMétadonnées seulementLes Saints de glace, Saint Médard et les autres...(Oron-la-Ville: Stratus, 1986)
- PublicationMétadonnées seulementLe climat des Romands(Oron-la-Ville: Stratus, 1993)