Glaciers of the Adamello-Presanella Group (Central Alps, Italy): areal and volume reductions since the Little Ice Age.

More than one hundred glaciers (including the widest glacier of the Italian Alps, the Ghiacciaio dell'Adamello) are presently extended about 53 km2. As documented in other alpine sectors and in several other regions, glaciers of the Adamello-Presanella Group (Central Alps, Italy) reached their maximum Holocene extension during the Little Ice Age (LIA). LIA glaciers limits have been reconstructed on the basis of geomorphologic and glacial geologic field surveys and mapped at the scale of 1:10,000. More recent (XXth Century) glacier limits have been detected from historical maps and multitemporal aerial photographs. All the collected data have been georeferenced (photographic documents using a direct linear transformation to correct tilting and relief displacement) and managed using a GIS for evaluating the most relevant quantitative parameters. In particular, glacier area loss and volume reduction have been determined. More than 140 glaciers developed during the LIA covering an area almost the double of their present surface. Since the middle of the XIX Century there has been a vigorous reduction in thickness and area extension of glacier bodies, broken by brief and weak advances. The notable regression of the fronts is marked by withdrawals ranging from several hundred meters to more than 2000 m. About 90 of LIA glaciers (extended about 8 km2) are presently extinguished. The apparent conflicting numbers of LIA and active glaciers (140 LIA glaciers - 90 extinguished = 101 active glaciers!) can be explained considering the fragmentation of LIA glacial bodies induced by their retreat. Between the maximum LIA extension and 1983 AD, glaciers of the Presanella Group lost about 55% of the total area while the mean value for the entire Adamello- Presanella Group is about 50%. An additional reduction of about 25% occurred between 1983 and 1999 AD, of which about 15% between 1983 -1994 and about 10% between 1994 and 1995. Preliminary data on volumetric variations show that the glaciers of the Adamello-Presanella Group lost about 30 m3/m2 between 1850 and 1983 AD. Area loss and volumetric variations supply new data for reconstructing the environmental evolution and climatic history of the Central Italian Alps. The glacier retreat scenario gives us the possibility for better understanding glaciers dynamics and their behaviour in reacting to global environmental changes. Moreover, the enduring process of glacier retreat and ice melting in alpine environments enhances the risk of natural hazards. Finally, considering the great amount of water stored in alpine glaciers (easily available and substantially uncontaminated, this research is of particular interest (1) for estimating the amount of ice melting as a consequence of global warming, (2) for modelling future availability of melt-water, and (3) for better planning the correct management of water as natural resource.