Glacial Decline in the Gran Paradiso Massif (Western Italian Alps) Since the Little Ice Age: Quantitative Analysis From a Multitemporal Database

Alpine glaciers are among the most relevant indicators of climate variations as they modify their shape and size in response to changes of their mass balance. In the framework of detailed investigations concerning global changeinduced glacier variations and loss of water resources stored in the Italian glaciers, here we present a multitemporal analysis of glacier variations occurred in the Gran Paradiso Massif since the Little Ice Age (LIA). Detailed geomorphological and glacial geological field surveys and photointerpretation allowed us to reconstruct LIA glacial limits. Glacier limits outlined from multitemporal datasets (e.g. aerial photographs, historical maps) and all the collected datasets were organized in a multi-temporal dynamic glaciological database in GIS environment. The analysis considered about 80 glacial bodies (according to the CGI-CNR glacier inventory, 1957-1958) and provide quantitative data documenting a general glacial decline since the LIA accelerated during the last three decades. Our results highlight a loss of about the 70% of the glacierized surface since the LIA and confirm, for this mountain group too, an areal reduction of over 45% in the last 60 years (1952-2015). We obtained new areal reduction rates that show dramatic variations, in particular they show a strong acceleration from -0,5% y-1 during second half of 19th century to ≈-1,4% y-1 in the period 1994-2015. Time-Distance curves, based on annual glaciological surveys conducted since the end of the 19th Century by the Italian Glaciological Committee and validated on multitemporal aerial photographs, confirm that these glaciers have been characterized by a general trend of retreat, particularly marked since the ‘90s. Results underline the strong imbalance of glaciers in the Western Alps and highlight the rapid increase in their reduction rate during the last decades, which is leading to impressive changes and to a relevant increase of the geomorphological hazard in the newly formed paraglacial environment.