Montagne | EPFL Graph Search

vignette|alt=Vue oblique distante de montagnes enneigées séparant un plateau aride d'une mer de nuages.|Vue d'une partie de l'Himalaya, avec l'Everest (près du centre), et du plateau tibétain depuis la Station spatiale internationale. vignette|alt=Un sommet couvert de glace sculptée en lames de rasoir, parcouru en son milieu par une rimaye et à ses pieds par une crevasse, avec deux groupes d'alpinistes visibles en tout petit.|Vue d'alpinistes (coin inférieur droit) évoluant entre une rimaye et une crevasse sur l'Alpamayo, au Pérou. Une montagne () est une forme topographique de relief positif, à la surface de planètes telluriques, et faisant partie d'un ensemble — une chaîne de montagnes — ou formant un relief isolé. Elle est caractérisée par son altitude et, plus généralement, par sa hauteur relative, voire par sa pente. Il n'existe toutefois pas de définition unique de ce qu'est une montagne, terme apparu entre le et le , et de nombreux régionalismes coexistent pour décrire les for

Urban Greenhouse Gas Emissions Monitoring in Davos, Switzerland, Before, During and After the World Economic Forum Annual Meeting 2012

Michael Lehning

Efforts to reduce anthropogenic greenhouse gas emissions require validation. Atmospheric measurements capture all emissions, and provide a unique and powerful means of continuous validation and feedback. To demonstrate the utility of real time greenhouse gas measurements, in-situ GHG mixing ratio instruments were deployed in Davos, Switzerland to measure emissions from the city before, during and after theWorld Economic Forum (WEF). Three Instruments were deployed at two separate locations over 3 months (late December 2011 to February 2012). One site was located in the middle of the Davos urban area and a second site was located out of the valley in the surrounding mountains. Carbon Dioxide (CO2), Methane (CH4), Carbon Monoxide (CO) and water vapor (H2O) were measured continuously by Picarro G2401 instruments at both sites. Additionally, a Picarro flux analyzer was deployed in the city to evaluate the inverse fluxes. The mesoscale atmospheric model, WRF nudged to meteorological observations (WRF-FDDA), was used to simulate the transport of GHG over the valley of Davos at 1.3km resolution. A Mini Micro Pulse LiDAR (MiniMPL) from Sigma Space was deployed to evaluate the simulated planetary boundary layer depth from the WRF-FDDA model. The initial flux estimates for CO2 were constructed based on inventories reported for 2005. CO2 mixing ratio measurements prior to WEF suggest the difference between modeled (real-time) and inventory (annual) emissions to be on the order of +40%. The enhancement is likely due to the increased use of heating fuel in the winter.We present here the temporal variability in the inverse fluxes, which are correlated with a cold wave severely affectingWestern Europe during the past winter, as well as changes in anthropogenic activities during the week of the WEF meeting. Also presented are new analyses of composite diurnal cycles of hourly CO/CO2 ratios, which provide additional information on the contributions of traffic relative to heating fuel. The absence of traffic peaks during the WEF meeting, indicate a change in road emissions potentially responsible for the observed decrease in the city emissions during the meeting. Acknowledgments: Calibration tanks were provided by C. Sweeney, NOAA ESRL.

2013

The European mountain cryosphere: a review of its current state, trends, and future challenges

Wolf Hendrik Huwald, Michael Lehning

The mountain cryosphere of mainland Europe is recognized to have important impacts on a range of environmental processes. In this paper, we provide an overview on the current knowledge on snow, glacier, and permafrost processes, as well as their past, current, and future evolution. We additionally provide an assessment of current cryosphere research in Europe and point to the different domains requiring further research. Emphasis is given to our understanding of climate–cryosphere interactions, cryosphere controls on physical and biological mountain systems, and related impacts. By the end of the century, Europe’s mountain cryosphere will have changed to an extent that will impact the landscape, the hydrological regimes, the water resources, and the infrastructure. The impacts will not remain confined to the mountain area but also affect the downstream lowlands, entailing a wide range of socio-economical consequences. European mountains will have a completely different visual appearance, in which low- and mid-range-altitude glaciers will have disappeared and even large valley glaciers will have experienced significant retreat and mass loss. Due to increased air temperatures and related shifts from solid to liquid precipitation, seasonal snow lines will be found at much higher altitudes, and the snow season will be much shorter than today. These changes in snow and ice melt will cause a shift in the timing of discharge maxima, as well as a transition of runoff regimes from glacial to nival and from nival to pluvial. This will entail significant impacts on the seasonality of high-altitude water availability, with consequences for water storage and management in reservoirs for drinking water, irrigation, and hydropower production. Whereas an upward shift of the tree line and expansion of vegetation can be expected into current periglacial areas, the disappearance of permafrost at lower altitudes and its warming at higher elevations will likely result in mass movements and process chains beyond historical experience. Future cryospheric research has the responsibility not only to foster awareness of these expected changes and to develop targeted strategies to precisely quantify their magnitude and rate of occurrence but also to help in the development of approaches to adapt to these changes and to mitigate their consequences. Major joint efforts are required in the domain of cryospheric monitoring, which will require coordination in terms of data availability and quality. In particular, we recognize the quantification of high-altitude precipitation as a key source of uncertainty in projections of future changes. Improvements in numerical modeling and a better understanding of process chains affecting high-altitude mass movements are the two further fields that – in our view – future cryospheric research should focus on.

2018