Fig. 3: Warming air temperatures correlate with interannual fluctuations in rockfall, with recent activity associated predominantly with warm spring temperatures.
From: Rockfall from an increasingly unstable mountain slope driven by climate warming
Interannual correlations between rockfall and air temperatures were assessed across various time windows starting on 15 May of the year preceding tree damage and ending on 30 September of the year in which damage occurred. a, From 1920 to 2020, warm temperatures positively influence rockfall across a range of shorter (30 days) to longer (450 days) time windows, with highest correlations observed for 13 July–26 August (45 days; r = 0.48, p < 0.01). In addition, the significant correlations found from early June (around day of year 160) to early December (340) in the year preceding rockfall and window widths of 280 to 450 days point to some delay—or a lag—between the driver and actual trigger of rockfall. The hat enhanced rockfall occurs when consecutive warm summers are recorded, probably favouring instability through the melting and destabilization of frozen ground at larger-than-normal depths. b, Between 1920 and 1969, the highest correlation extends from 2 July–27 August (57 days; r = 0.41, p < 0.01). c, After 1970, rockfall activity correlates best with warm air temperatures in spring (27 April–28 May; 32 days; r = 0.47, p < 0.01) and to a lesser degree to summer warmth (14 July–16 August; 33 days; r = 0.39, p < 0.01).
