Variation in the Occurrence of Rainfall Events Triggering Landslides

We analyze the climatic features of the Vicenza Province (NE Italy) and the characteristics of the exceptional rainfall event that hit the area in November 2010, triggering a huge number of landslides. Our analysis aims at identifying the hydrological variable related to the triggering of the recorded instabilities and the recent variation in the occurrence of rainfall events inducing landslides. During the period 1920–2009, a negative trend in the annual rainfall and a marked positive trend of the mean annual temperature have been observed in the study area. Rainfall has become more concentrated during autumnal season (October–December) and the greatest increase in temperature has been registered in winter (January–March) and summer (June–August). As a consequence, the quantity of meteoric water available for infiltration and run off processes has increased in autumn, which has typically been the season with the maximum number of landslides. Moreover, the statistical analysis of annual rainfall maxima for durations of 1, 3, 6, 12 and 24 h, and 1, 2, 5, 10, 30, 60, 90, and 120 days, allowed us to highlight that the occurrence of intense rainfall events has increased in the last 20 years. Our results show that the degree of rainfall-induced landslide hazard has increased in the study area, possibly due to recent climate changes. In the near future, such results should be taken into account for landslide forecasting, monitoring and mitigation.