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Rebetez, Martine

Nom
Rebetez, Martine
Affiliation principale
Site web
Fonction
Professeure ordinaire
Email
martine.rebetez@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/403

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  • Publication
    Accès libre
    An analysis of the July 2006 heatwave extent in Europe compared to the record year of 2003
    (2009)
    Rebetez, Martine 
    ;
    Dupont, Olivier
    ;
    Giroud, Marianne
    Recent analyses have identified summer warming trends in Europe in recent decades, culminating in 2003, when mean summer temperatures were exceptionally hot over much of Europe. Mean monthly temperatures were very high in July 2003 and reached record levels in both June and August. In 2006, the mean monthly temperature for July reached a record high. Our analysis of temperature observations shows that in July 2006, as in summer 2003, maximum temperatures were more abnormal than minimum values. The 2006 heatwave was located more to the north than in 2003, and particularly affected the Netherlands, Belgium, Germany, Poland, France and Switzerland. The July 2006 anomalies were similar in magnitude to those of June and August 2003, but the discrepancy between minimum and maximum temperature anomalies was larger in 2006 compared to both June and August 2003. For maximum temperature, the affected land area by anomalies higher than 4-6 K was largest in July 2006, although the anomalies were higher in June and August 2003 at the most anomalous sites. In the north of Europe, the absolute monthly temperature values were higher in July 2006 compared to both June (also on the Iberian Peninsula) and August 2003.
  • Publication
    Accès libre
    Monthly air temperature trends in Switzerland 1901-2000 and 1975-2004
    (2008)
    Rebetez, Martine 
    ;
    Reinhard, Michael
    We analysed long-term temperature trends based on 12 homogenised series of monthly temperature data in Switzerland at elevations between 316 m.a.s.l. and 2490 m.a.s.l for the 20(th) century (1901-2000) and for the last thirty years (1975-2004). Comparisons were made between these two periods, with changes standardised to decadal trends. Our results show mean decadal trends of +0.135 degrees C during the 20(th) century and +0.57 degrees C based on the last three decades only. These trends are more than twice as high as the averaged temperature trends in the Northern Hemisphere. Most stations behave quite similarly, indicating that the increasing trends are linked to large-scale rather than local processes. Seasonal analyses show that the greatest temperature increase in the 1975-2004 period occurred during spring and summer whereas they were particularly weak in spring during the 20(th) century. Recent temperature increases are as much related to increases in maximum temperatures as to increases in minimum temperature, a trend that was not apparent in the 1901-2000 period. The different seasonal warming rates may have important consequences for vegetation, natural disasters, human health, and energy consumption, amongst others. The strong increase in summer temperatures helps to explain the accelerated glacier retreat in the Alps since 1980.
  • Publication
    Accès libre
    Climate change may already threaten Scots pine stands in the Swiss Alps
    (2004)
    Rebetez, Martine 
    ;
    Dobbertin, Matthias
    Large 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.
  • Publication
    Accès libre
    Summer 2003 maximum and minimum daily temperatures over a 3300 m altitudinal range in the Alps
    (2004)
    Rebetez, Martine 
    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.
  • Publication
    Métadonnées seulement
    To what extent can oxygen isotopes in tree rings and precipitation be used to reconstruct past atmospheric temperature? A case study
    (2003)
    Rebetez, Martine 
    ;
    Saurer, Matthias
    ;
    Cherubini, Paolo
    We analyzed the relationship between air temperature and oxygen isotopes measured in tree rings of silver fir (Abies alba Mill.) from a long-term forest ecosystem research plot in the Swiss Jura mountains (LWF project). The oxygen isotope data were compared with a century-long meteorological series of air temperature data. Measurements of oxygen isotope ratios in precipitation were also used for comparison. Results show that the late-wood tree-ring series is significantly correlated with May to August temperatures. Correlations were higher for maximum (daytime) air temperature and even better for air temperature measured on rainy days only. We stress that trends in maximum temperature series for this time of the year, like trends in oxygen isotope ratios series from tree rings, are completely different from trends in yearly mean temperature. Indeed, maximum temperature trends during the vegetation period slightly decreased during the 20th century, whereas yearly means increased strongly.
  • Publication
    Accès libre
    An analysis of regional climate-change in Switzerland
    (1994)
    Beniston, Martin
    ;
    Rebetez, Martine 
    ;
    Giorgi, F
    ;
    Marinucci, M
    An analysis of daily climatological data covering the period from 1901 to 1992 for four locations in Switzerland (Zurich, Lugano, Davos, and Santis) has been made. The study has highlighted the fact that climate change this century is characterized by increases in minimum temperatures of about 2K, a more modest increase in maximum temperatures (in some instances a decrease of maxima in the latter part of the record), little trend in the precipitation data, and a general decrease of sunshine duration through to the mid 1980s. The interannual variability is generally large, and filtering of the data to remove high-frequency noise shows that the regional climate undergoes a series of fluctuations of between 8 and 20 years' duration. The temperature change over this century is of greater magnitude than the global temperature changes published in the literature, reflecting an amplification of the global signal in the Alpine region; warming has been most intense in the 1940s, followed by the 1980s; the cooling which intervened from the 1950s to the late 1970s was not sufficient to offset the warming in the middle of the century. Pressure statistics have been compiled as a means of providing a link between the regional-scale climatological variables and the synoptic, supra-regional scale. These statistics show that pressure also exhibits a number of decadal-scale fluctuations, with the appearance of a new and anomalous behavior in the 1980s; in this decade, pressure reaches annual average values far higher than at other times this century. The pressure field is well correlated with the North Atlantic Oscillation (NAO) Index for distinct periods of the record (1931-1950 and 1971-1990) and is almost decorrelated from the NAO Index for the other decades of the century; this is indicative of transition from one climatic regime to another, dominated by zonal flow when the correlation with the NAO Index is high. In the 1980s, when zonal flow over the North Atlantic is strong, episodes of persistent, anomalously high pressures (blocking highs) are seen to occur over Switzerland, particularly during the winter season. The difference between the zonal and non-zonal regimes is particularly marked between the decade of the 1950s and that of the 1980s. The impact of this change between the 1950s and the 1980s on a number of climatological variables has been investigated statistically in order to provide an illustration of the manner in which changes in synoptic regimes (i.e., 'climate change') impacts upon climate characteristics on a regional scale. The analysis shows that temperature, precipitation, snow depth, and sunshine duration are indeed sensitive to large-scale influences; not only can yearly mean changes be quantified, but also seasonal and monthly fluctuations.