Sensitivity of Mass Balance and Equilibrium Line Altitude to Climate Change in the French Alps

Wednesday, 17 December 2014
Delphine Six, LGGE Laboratoire de Glaciologie et Géophysique de l’Environnement, Saint Martin d'Hères, France
Assessment of the sensitivity of surface mass balance and equilibrium line altitude to climate change is crucial for the simulation of the future evolution of glaciers. Such an assessment has been carried out using a very extensive data set comprising numerous measurements of snow accumulation and snow and ice ablation made on four French glaciers over the last 16 years. Winter mass balances show a complicated pattern with respect to altitude, showing no clear linear relationship. Although the ratios of winter mass balance to valley precipitation differ considerably from one site to another, they remain relatively constant over time. Relationships between snow/ice ablation and temperature are stable, showing no link with altitude. The mean snow and ice PDD factors found are 0.003 and 0.0061 m w.e. °C-1 d-1. This analysis shows that, at a given site, ablation depends mainly on the amount of snow precipitation and on cumulative positive degree days. The sensitivity of annual ablation to temperature change increases almost linearly from 0.25 m w.e. °C-1 at 3500 m to 1.55 m w.e. °C-1 at 1650 m. Equilibrium line altitude sensitivity to temperature change was found to ranges from 50 m °C-1 to 85 m °C-1, generally lower than previous studies.