Climatic drivers of seasonal glacier mass balances: an analysis of 6 decades at Glacier de Sarennes (French Alps)

Abstract

Refined temporal signals are extracted from a glacier winter and summer mass balance series recorded at Glacier de Sarennes (French Alps) using variance decomposition. They are related to local and synoptic meteorological data in terms of interannual variability and structured trends. The winter balance has increased by +23% since 1976 due to more precipitation in early and late winter. The summer balance has decreased since 1982 due to a 43% increase in snow and ice melt. A 24-day lengthening of the ablation period – mainly due to longer ice ablation – is the main component in the overall increase in ablation. In addition, the last 25 yr have seen increases in ablation rates of 14 and 10% for snow and ice respectively. A simple degree-day analysis can account for both the snow/ice melt rate rise and the lengthening of the ablation period as a function of higher air temperatures. From the same analysis, the equilibrium line altitude of this 45° North latitude south-facing glacier has sensitivity to temperature of +93 m °C<sup>−1</sup> around its mean elevation of 3100 m a.s.l. over 6 decades. The sensitivity of summer balance to temperature is −0.62 m w.e. yr<sup>−1</sup> °C<sup>−1</sup> for a typical 125-day long ablation season. Finally, the time structure of winter and summer mass balance terms are connected to NAO anomalies. Best correlations are obtained with winter NAO anomalies. However, they strongly depend on how the NAO signal is smoothed, so that the link between mass-balance seasonal terms and NAO signal remains tenuous and hard to interpret

Causes of Glacier Melt Extremes in the Alps Since 1949

“…Sarennes is a south facing glacier (0.09 km 2 in 2015) with a limited altitude range of 150 m between 2,850 and 3,000 m above sea level, located in the Grande Rousses range (45°07′N, 6°07′E, French Alps). Since 1949, systematic winter, and summer mass balance measurements have been carried out, from which annual balances are calculated (Thibert et al, ; Text S1). Sarennes provides detailed point‐mass balance observations repeated year to year at the same locations, forming one of the longest series worldwide (World Glacier Monitoring Service, ; Zemp et al, ).…”

“…However, this theory has never been applied to glacier mass balance series to assess the rareness of mass loss extremes. For this purpose, we propose to analyze the long‐term mass balance recorded at Sarennes glacier (Thibert et al, ), acknowledged to be of great value for inferring climatic fluctuations at high altitudes in the Alps in the second half of the twentieth century (Thibert et al, ; Vincent et al, ). Mass balance and melt variations are indeed very similar at the European Alps scale (Letréguilly & Reynaud, ; Vincent et al, , ); therefore, an analysis from this single glacier should have a wide spatial significance.…”

Impact du réchauffement climatique sur l'activité avalancheuse et multiplication des avalanches humides dans les Alpes françaises

“…L'augmentation relative de l'activité avalancheuse sur la période 1960-1980 correspond bien à des hivers plus rigoureux, par ailleurs bien documentés par d'autres indicateurs climatiques (courtes avancées glaciaires notamment que des méthodes d'analyse similaires permettent de mettre en évi-dence [Thibert et al, 2013]). Le « recul des avalanches » ensuite observé, accompagné d'une diminution de la proportion des avalanches avec aérosol s'inscrit quant à lui dans une période de réchauffement marqué.…”

Changements climatiques et risques naturels dans les Alpes

“…Celui-ci n'existe que pour quelques glaciers, principalement ceux suivis par l'observatoire GLACIOCLIM (tableau 4 ; Vincent, 2002). Les variations saisonnières du glacier de Sarennes depuis 1949 quantifient ainsi fidèlement l'évolution des chutes de neige hivernales et de la température estivale à haute altitude (Thibert et al, 2013). Rabatel et al, 2013).…”