Recent glaciers variations in Alta Valtellina (Ortles-Cevedale Group, Italian Alps): quantitative analysis of a strong glacial decline during the last 60 years

Alpine glaciers are very sensitive to climate variations that modify their shape and size in response to changes in their mass balance. In the framework of detailed investigations concerning global change-induced glacier variations and loss of water resources stored in the Italian glaciers, this work presents an analysis of recent changes (1954-2012) in the Alta Valtellina’s glaciers (Ortles-Cevedale Group). The analysis was based on a multi-temporal dataset of aerial photographs and historical maps, which have been organized and processed in a multi-temporal glaciological database using Geographic Information Systems (GIS). This work provides quantitative evidence of accelerated glacial decline, in particular since the end of the 20th century. Our results highlight an areal reduction of about 45% in the last 60 years, with a strong increase in the areal reduction rate from -0,51% y-1 during 1954-1982 to -1,26% y-1 during 1982-2012. Applying empirical formulas of volume-area scaling, we estimate a volume loss of about 45%, corresponding to about 700 million m3, for the period 1954-2012. More than 400 million m3 have been lost in the period from 1982 to 2006. Geodetic mass balance calculations for the 1982-2006 time interval indicate a strongly negative annual balance of about 0,55 m w.e. yr-1, and also suggest that volume loss estimates require a correction factor of 1.3. Results underline the strong imbalance of glaciers in the study area, and highlight the rapid increase in their reduction rate during the last decades, which is leading to impressive change in glacier shape and dimensions.