Ten new long-term glaciological mass balance series for Swiss glaciers

Abstract:

The surface mass balance of mountain glaciers is a valuable indicator of climate change. Globally coordinated monitoring efforts have contributed to a comprehensive set of time series documenting variations in glacier-wide mass balance for about a hundred glaciers. However, only few series are longer than twenty years and even less start before the 1980s. Glaciers in the European Alps are most densely covered with mass balance records. However, given the strong differences in the response of individual glaciers as well as the partly poor representativeness of some series for their respective region, more direct information on mass balance variability is required even in the Alps. Furthermore, only a small fraction of the records yields seasonal mass budget components which are of eminent importance for understanding glacier response to shifts in climatic forcing throughout the 20^th century. In this study, we present ten new long-term series of glacier-wide seasonal mass balance for glaciers in the Swiss Alps partly starting in the 1950s and continued until today. Previously unpublished and unevaluated measurements of point winter and summer balance form the base of these records. Data was compiled from old archives and from various sources. Most of the in-situ measurements were not intended as full monitoring programs which might explain that these highly valuable data sets were not consistently evaluated so far and were thus unavailable to the scientific community.

Using a new technique employing modelling for spatial extrapolation and homogenization of the seasonal point measurements we infer continuous series of area-averaged mass balance. The results are validated against independent decadal ice volume changes from photogrammetric surveys. Five of the new seasonal mass balance series cover more than 50 years and add a substantial amount of information on the dynamics of regional glacier mass change. This will strengthen the worldwide data collection on glacier monitoring, especially during the data-sparse period before the 1980s which is characterized by notable regime changes. We compare our results to existing long-term series and present an updated assessment of mass balance variability and sensitivity throughout the European Alps in connection with external drivers.