Browsing by Autor "Emmanuel Thibert"

Now showing 1 - 6 of 6

A Nonlinear Statistical Model for Extracting a Climatic Signal From Glacier Mass Balance Measurements
(Wiley, 2018) Christian Vincent; Álvaro Soruco; M Azam; Rubén Basantes-Serrano; Miriam Jackson; Bjarne Kjøllmoen; Emmanuel Thibert; Patrick Wagnon; Delphine Six; Antoine Rabatel
Abstract Understanding changes in glacier mass balances is essential for investigating climate changes. However, glacier‐wide mass balances determined from geodetic observations do not provide a relevant climatic signal as they depend on the dynamic response of the glaciers. In situ point mass balance measurements provide a direct signal but show a strong spatial variability that is difficult to assess from heterogeneous in situ measurements over several decades. To address this issue, we propose a nonlinear statistical model that takes into account the spatial and temporal changes in point mass balances. To test this model, we selected four glaciers in different climatic regimes (France, Bolivia, India, and Norway) for which detailed point annual mass balance measurements were available over a large elevation range. The model extracted a robust and consistent signal for each glacier. We obtained explained variances of 87.5, 90.2, 91.3, and 75.5% on Argentière, Zongo, Chhota Shigri, and Nigardsbreen glaciers, respectively. The standard deviations of the model residuals are close to measurement uncertainties. The model can also be used to detect measurement errors. Combined with geodetic data, this method can provide a consistent glacier‐wide annual mass balance series from a heterogeneous network. This model, available to the whole community, can be used to assess the impact of climate change in different regions of the world from long‐term mass balance series.
Contribution of glacier runoff to water resources of La Paz city, Bolivia (16° S)
(Cambridge University Press, 2015) Álvaro Soruco; Christian Vincent; Antoine Rabatel; Bernard Francou; Emmanuel Thibert; Jean Emmanuel Sicart; Thomas Condom
Abstract The supply of glacier water to La Paz city, Bolivia, between 1963 and 2006 was assessed at annual and seasonal timescales based on the mass-balance quantification of 70 glaciers located within the drainage basins of La Paz. Glaciers contributed ∼15% of water resources at an annual scale (14% in the wet season, 27% in the dry season). Uncertainties in our estimation are related to the assumed constant precipitation (∼0.5% for ice-free areas and up to 6.5% for glaciated areas), the constant runoff coefficient (∼1%), the surface areas of the glaciers and catchments (∼5%) and the mean mass-balance uncertainty of the 21 glaciers used to obtain the mass balance of the 70 glaciers (12% of the total discharge). Despite the loss of 50% of the glacierized area during the study period, runoff at La Paz did not change significantly, showing that increase in ice melt rates compensated for reduction in the surface area of the glaciers. In the future, assuming complete disappearance of the glaciers and no change in precipitation, runoff should diminish by ∼12% at an annual scale, 9% during the wet season and 24% during the dry season.
Glacier mass balance determination by remote sensing in the French Alps: progress and limitation for time series monitoring
(2004) J.-P. Dedieu; Antoine Rabatel; Christian Vincent; François Valla; Emmanuel Thibert; Yves Arnaud
This paper presents an approach founded on an indirect methodology to determine the distribution of mass balance at high spatial resolution using remote sensing and ground stakes measurements. A recent time series of images from optical and SAR data are selected on 3 outlet glaciers well suited in the French Alps to evaluate the accuracy of the computed mass balance. The method is based on the snowline determination as a proxy of the equilibrium line altitude (ELA). The key of the transfer is the activity coefficient (db/dz) for the annual mass balance calculation. Comparison between measured and computed mass balance provide a good correspondence (R/sup 2/=0.90) and allows extending the method on large-scale areas. The limitations are cloudiness for optical data and high slope distortion on SAR images.
Merging terrestrial laser scanning technology with photogrammetric and total station data for the determination of avalanche modeling parameters
(Elsevier BV, 2014) Alexander Prokop; Peter Schön; Florian Singer; Gaëtan Pulfer; Mohamed Naaïm; Emmanuel Thibert; Álvaro Soruco
The full-scale avalanche test-site at Lautaret Pass (French Alps)
(Elsevier BV, 2015) Emmanuel Thibert; Hervé Bellot; Xavier Ravanat; Frédéric Ousset; Gaëtan Pulfer; Mohamed Naaïm; Pascal Hagenmuller; Florence Naaim-Bouvet; Thierry Faug; Kouichi Nishimura
The full-scale avalanche test site at Lautaret Pass in the southern French Alps has been used by IRSTEA-Cemagref Research Institute since 1972. Over recent years, two avalanche paths have been used routinely to release avalanches and study avalanche dynamics and interactions between avalanches and obstacles. Avalanche flows are generally dense and dry, sometimes with a powder cloud on top. Main avalanche path no. 2 is dedicated to studies on avalanche dynamics. Within the flow of the avalanche, flow height and vertical profiles of pressure and velocity are measured along a 3.5 m tripod. The snow volume released in the release zone is quantified by differential analysis of laser scanning measurements performed before and after triggering. High-speed positioning of the avalanche front along the track is carried out by terrestrial oblique photogrammetry. Above the dense layer, the upper layer of the avalanche is characterized by particle and air flux measurements. Avalanche path no. 1 is smaller in size and particularly well-suited to experiments on structures exposed to small to medium-size avalanches (< 1000 m3). A macroscopic sensor structure consisting of a one square-meter plate supported by a 3.5 m high steel cantilever beam is fixed in the ground, facing the avalanche. Impact pressures are reconstructed from the beam deformations and avalanche velocity is measured by optical sensors. For these experimental devices dedicated to improving our understanding of avalanche physics, a national and international partnership has been developed over the years, including INSA de Lyon, CNRS and Université Joseph Fourier (France), Aalto University (Finland), Nagoya University (Japan), Boku University (Austria) and IGEMA (Bolivia).
Volume and frequency of ice avalanches from Taconnaz hanging glacier, French Alps
(Cambridge University Press, 2014) Christian Vincent; Emmanuel Thibert; M. Härter; Álvaro Soruco; Adrien Gilbert
Abstract Very large volumes of ice break off regularly from Taconnaz hanging glacier, French Alps. During winter, when the snow mantle is unstable, these collapses can trigger very large avalanches that represent a serious threat to inhabited areas below. Photogrammetric measurements have been performed over 1 year to assess the volume and frequency of the largest collapses. Major collapses occur when the glacier reaches a critical geometry. After a major ice collapse, the glacier is in a minimal position and subsequently recharges over 6 months to reach the maximum position again. This critical geometry is a necessary but not sufficient condition for further large collapses. Large collapses do not systematically occur in the maximum position, as ice is often removed by disintegration into small ice blocks. For two major collapses, the volume of ice breaking off has been assessed at ~275 000 m 3 . Photogrammetric measurements were used to determine an ice flux of 820 000 m 3 a –1 through the studied ice stream, in agreement with an assessment based on ice-flow modeling. This ice flux estimation was used to determine the average ice volumes breaking off over surveyed periods.