Evidenze preliminari del recente aumento di temperatura in alcune grotte delle Alpi occidentali (2012-2021)

The physical processes underlying climatic conditions in subterranean environments are still largely unexplored. Evidence in literature pointed out that the temperature of a cave is closely related to the external annual temperature without its wide fluctuations and this temperature compression is more or less evident depending on the cave characteristics. Hence, global climate change is expected to affect the geophysical balance of the subterranean environment, but the role of cave characteristics in modulating the compression of the temperature signal is still largely unknown. This research work investigates the relation between cave temperature and surface temperature to verify whether the impact of temperature variation can be recorded in subterranean environments. To achieve this aim, a comparative analysis between temperature data collected during a five-month period in 2012-2013 (period A) and in 2020-2021 (period B) was performed in eight Western Alpine caves. In each cave, two i-button dataloggers were placed, the first one at the cave entrance and the second one deeper in the cave. Dataloggers were set to record temperatures every six hours and data were then daily aggregated. For each cave, temperatures measured in the deepest part of the cave were then compared with: i)temperatures measured at the entrance of the cavity; and ii)temperatures obtained from the closest meteorological station. A climatic analysis of each cave area has also been performed, working on twenty years of daily data obtained from the meteorological station closer to each cave (max and min temperature and precipitation) in order to identify the main trends relative to precipitation and temperature in the area. In all examined caves temperature variations in the inner zone of the caves always show a lower excursion range compared to the temperature variations observed at the entrances, which, in turn, always show lower temperature excursions than those observed in the weather stations. In addition, the range of thermal excursions of the caves strongly depends on the morphology of the cave, its depth, and its level of thermic insulation, with wider excursions in shallower caves compared to deeper ones. In order to evaluate potential changes across the considered timeframe, the differences in maximum (Tx) and minimum (Tn) temperature between the two considered periods were calculated highlighting that seven of the eight considered caves showed an increase of the average Tx from period A to period B; regarding Tn, five caves showed an increase of the average Tn from period A to period B. Maximum and minimum temperature trends were also calculated over a ten years period (from 2012 to 2021) for each cave area using daily data from the meteorological station closer to each cave. The results obtained in the frame of the climatic analysis highlighted some differences in temperature patterns among caves: on the one hand, shallower caves are subject to external temperature fluctuations even in the short term; on the other hand, caves with greater planimetric extension are generally characterized by a remarkable thermal stability and their internal temperature variation seems to be buffered from external variation. Therefore, they may represent insightful systems for monitoring temperature increases driven by climate change as they allow us to clearly track the temperature trends occurring outside, without confounding effects induced by other climatic factors.