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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
    Detecting and correcting sensor drifts in long-term weather data
    (2013)
    von Arx, Georg
    ;
    Dobbertin, Matthias
    ;
    Rebetez, Martine 
    Quality control of long-term monitoring data of thousands and millions of individual records as present in meteorological data is cumbersome. In such data series, sensor drifts, stalled values, and scale shifts may occur and potentially result in flawed conclusions if not noticed and handled properly. However, there is no established standard procedure to perform quality control of high-frequency meteorological data. In this paper, we outline a procedure to remove sensor drift in high-frequency data series using the example of 15-year-long sets of hourly relative humidity (RH) data from 28 stations subdivided into 202 individual sensor operation periods. The procedure involves basic quality control, relative homogeneity testing, and drift removal. Significant sensor drifts were observed in 40.6 % of all sensor operation periods. The drifts varied between data series and depended in a complex, usually inconsistent way on absolute RH values; within single series for instance, a drift could be negative in the lower RH range and positive in the upper RH range. Detrending changed RH values by, on average, 1.96 %. For one fifth of the detrended data, adjustments were 2.75 % and more of the measured value, and in one tenth 4.75 % and more. Overall, drifts were strongest for RH values close to 100 %. The detrending procedure proved to effectively remove sensor drifts. The principles of the procedure also apply to other meteorological parameters and more generally to any time series of data for which comparable reference data are available.
  • Publication
    Accès libre
    Spatio-temporal effects of forest canopy on understory microclimate in a long-term experiment in Switzerland
    (2012)
    von Arx, Georg
    ;
    Dobbertin, Matthias
    ;
    Rebetez, Martine 
    Forest canopy generally moderates below-canopy air temperature and relative humidity and thus creates a specific microclimate for tree seedling growth. Climate change will alter the moderating capacity, which may render the below-canopy conditions unsuitable for recruitment of the hitherto dominant tree species. We assigned long-term meteorological data (1997-2010) recorded inside and outside of 14 different forest ecosystems in Switzerland to three forest types (broadleaved, non-pine conifer, pine), two altitudinal levels (low, high), the four seasons and general weather situations (normal, hot/dry, cold/wet) to compare moderating capacity of each of these classifiers. Our results confirmed a general moderating effect of canopy on below-canopy microclimate with a decrease of daily maximum air temperature of up to 5.1 degrees C (overall average: 1.8 degrees C) and an increase of daily minimum relative humidity of up to 12.4% (overall average: 5.1%) in the long-term average, respectively. Broadleaved and non-pine conifer forests moderated daytime microclimate about twice as much as pine forests, while at nighttime considerably less cooling down and even negative effects on levels of relative humidity compared to the open area were recorded at the pine forest sites. Moderating capacity was stronger at low altitude than at high altitude. It was strongest during the growing season, particularly in summer, and depended in a complex way on the general weather situation. Deviations from the general seasonal and weather condition patterns most likely occurred when soil moisture pools were depleted. Despite the moderating capacity, below-canopy microclimate did not lag behind open area microclimate. Based on our results we conclude that natural recruitment in pine forests and high-altitude forests may respond most sensitively to climate change. (c) 2012 Elsevier B.V. All rights reserved.
  • Publication
    Accès libre
    Relating remotely sensed forest damage data to wind data: storms Lothar (1999) and Vivian (1990) in Switzerland
    (2012)
    Usbeck, Tilo
    ;
    Waldner, Peter
    ;
    Dobbertin, Matthias
    ;
    Ginzler, Christian
    ;
    Hoffmann, Christian
    ;
    Sutter, Flurin
    ;
    Steinmeier, Charlotte
    ;
    Volz, Richard
    ;
    Schneiter, Gustav
    ;
    Rebetez, Martine 
    This study compares the surface wind speed and forest damage data of two exceptionally severe winter storms, Vivian 1990 and Lothar 1999. The study area comprises the region that suffered damage in Switzerland. The wind speed data were derived from simulations of MeteoSwiss (Federal Office of Meteorology and Climatology), measurements during the storm periods and expert analyses of the data. The remotely sensed forest damage data were provided by the Federal Office for the Environment and the forest cover data by Swiss Federal Statistical Office. We compared data on the peak gust and maximum average wind speed, with data on the spatially related forest area and forest damage area, and found some clear differences in the correlations between the different wind data and forest damage. Our results point generally to the damage-causing role of near-surface gusts at maximum wind speeds during the storm. These tended to be spatially distributed on a fine scale. In only a few cases were the results statistically significant. However, these results could probably be improved with better wind data. For example, gust measurements spatially closer to forests or simulations of gusts at maximum wind speed could be produced with a spatially higher resolution.
  • Publication
    Accès libre
    Comparison between open-site and below-canopy climatic conditions in Switzerland for different types of forests over 10 years (1998-2007)
    (2011)
    Renaud, Valentine
    ;
    Innes, J. L.
    ;
    Dobbertin, Matthias
    ;
    Rebetez, Martine 
    We compared below-canopy and open-site climatic conditions for 14 different forest sites in Switzerland and analysed the forest influence on local summer and winter climate according to the forest type (coniferous, mixed, deciduous), soil type, slope orientation, basal area and tree height. We compared below-canopy and open-field data for minimum, maximum and daily mean temperature, relative humidity, maximum and daily mean photosynthetically active radiation (PAR) and wind speed from 1998 to 2007. We found clear differences between below-canopy and open-field temperatures, humidity, wind speed and PAR and could relate them to the specific site conditions and forest type. The forest influence on PAR and maximum temperature is clearly determined by the forest type, whereas the influence on minimum temperature is affected by both forest type and slope orientation and impact on humidity depends on the soil type. The wind speed is most impacted by topography and slope orientation.
  • Publication
    Accès libre
    Les chênes pubescents chassent-ils les pins sylvestres valaisans?
    (2006)
    Rigling, Andreas
    ;
    Dobbertin, Matthias
    ;
    Bürgi, Matthias
    ;
    Gimmi, Urs
    ;
    Graf Pannatier, Elisabeth
    ;
    Gugerli, Felix
    ;
    Heiniger, Ursula
    ;
    Polomski, Janina
    ;
    Rebetez, Martine 
    ;
    Rigling, Daniel
  • Publication
    Accès libre
    Die Klimaveränderung bedroht die Föhrenwälder im Wallis
    (2006)
    Rebetez, Martine 
    ;
    Dobbertin, Matthias
    ;
    Rigling, Andreas
    ;
    Graf Pannatier, Elisabeth
    ;
    Wohlgemuth, Thomas
  • 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.