Glaciers represent a major economic and societal issue (water resources, hazards, sea level change), the importance of which is reinforced in the current context of rapid change in climate forcing, surface conditions and anthropogenic pressure.
The glacier equilibrium line represents the place on the glacier where the surface mass balance is zero. It thus delineates, upstream, the accumulation zone (where the mass balance is positive) and, downstream, the ablation zone (where the mass balance is negative). From one year to the next, depending on climatic conditions, the altitude of the equilibrium line varies. Knowing its altitude each year and documenting its temporal variability therefore gives us information on climatic conditions and their evolution.
Traditionally and mainly due to the difficulty of access and the topographical complexity of glacial environments, glaciological data are derived from in situ measurements and are accessible on a very limited number of glaciers. Thus, in situ measurement of the equilibrium line altitude is carried out on an extremely small number of glaciers: around 40 glaciers have continuous measurements over more than 40 years (i.e. 0.016% of the total number of glaciers on Earth). Recent studies have shown the interest of high spatial resolution optical satellite remote sensing to regionalize the measurement of these variables (e.g. Rabatel et al., 2005, 2012, 2013, 2016, 2017).
The proposed product consists of the elevation of the annual glacier equilibrium line, measured at the end of the ablation period for all glaciers on a regional scale using optical spatial remote sensing. The characteristics of the product are the following:
- Satellite data sources: Sentinel-2, Landsat-5/8, ASTER, SPOT-6/7
- Frequency of publication: Annual
- Coverage: European Alps
A product without equivalent
The product Altitude of Annual Glacier Equilibrium Line has no equivalent in Europe (Copernicus) or the United-States (NSIDC). One of its strengths is that it relies on both in situ observations and remote sensing. Finally, this approach is in line with the monitoring strategy established internationally by the Global Terrestrial Network for Glaciers (GTN-G) and the Global Cryosphere Watch (GCW, WMO).
From a scientific perspective, the product fills a gap in glacier information both nationally and internationally. In terms of applications, it provides elements for a better characterization of the recent evolution of glaciers and the associated impacts (water resources, sea level) useful for land management.
240 glaciers in the European Alps
The product Altitude of Annual Glacier Equilibrium Line is available for a set of 240 glaciers in the European Alps over the period 2000-2016. The satellite data processing chain set up in the framework of Lucas Davaze’s thesis (2019, Univ. Grenoble Alpes) has been published (cf. Davaze et al. 2020, Supp. Mat.). Current considerations include the possibility of minimising human intervention in the production of the product and the production of the data.
Davaze, L., A. Rabatel, A. Dufour, R. Hugonnet, Y. Arnaud. 2020. Region-wide annual glacier surface mass balance for the European Alps from 2000 to 2016. Frontiers in Earth Science, Cryospheric Sciences, doi: 10.3389/feart.2020.00149