Rockfall triggering and meteorological variables in the Dolomites (Italian Eastern Alps)

Abstract. Alpine areas are experiencing substantial changes in both temperature and rainfall intensity, both critical triggers for rockfall events. To better understand these evolving climatic scenarios in the Dolomites from 1970 to 2019 and their implications for historical rockfall occurrences, we developed a novel approach based on the frequency analysis of meteorological variables. Our analysis considered key climate variables including mean air temperature, precipitation, thermal amplitude, freeze-thaw cycles, and icing, examined at various aggregation scales. Results unequivocally show a significant warming trend, with the highest warming rates (up to 0.3 °C per decade) observed during spring. This warming has led to an earlier onset of summer and a delayed end of winter, altering seasonal lengths. We also detected a notable decline in cold-related phenomena, with an estimated decrease of 7.3 freeze-thaw days and 2.2 icing days per decade. Precipitation patterns are changing too, with an increasing frequency of high-intensity rainfall events, particularly in winter, and a reduction in low-intensity events across all seasons. The Rescaled Adjusted Partial Sums (RAPS) method further confirmed long-term precipitation trends, revealing that climatic evolution is driven by shifts in variable frequencies rather than just extreme values. Employing a Bayesian method, we investigated the conditional probability of rockfall occurrences knowing that a meteorological variable is within a given range. Our findings reveal several key correlations: in the last decade high-intensity rainfall correlates with rockfalls in autumn, showing conditional probabilities of 12.4 % below 1000 m and 22.2 % between 1000–2000 m. Mean air temperature correlates with rockfalls in summer, for instance, with a 12.7 % probability for 21–24 °C between 1000–2000 m, and in autumn, such as a 2.2 % probability for 17.6–20.8 °C above 2000 m. Temperature amplitude shows high rockfall probabilities in spring, reaching 28.6 % for 8.8–9.9 °C below 1000 m, and in winter, with a 5.8 % probability for 9–10 °C between 1000–2000 m. Beyond these meteorological links, rockfall frequency exhibits three main peaks: November, February-April, and August. Regarding rockfall source aspect, north component has significant increment from 1970–1999 to 2000–2025 (from 4 % to 12 % +3 %) above 2000 m, a pattern likely linked to permafrost thawing. This study underscores the critical influence of changing climate dynamics on rockfall activity in Alpine environments, providing quantitative links between specific meteorological shifts and rockfall occurrence.