*3.1. Reconstructed Rainfall Events*

A total of 5231 rainfall events were identified by exploiting the database for the period of 2000–2018. Seventy-two percent of the events were detected in the cold season, while only 28% of the events were identified in warm periods, confirming the higher aridity index of warm months calculated for the study area (Figure 4b). In cold periods, the duration of the events ranged between 1 and 280 h, while cumulated amounts ranged between 1.0 and 285.0 mm. About 80% of the events were characterized by a duration lower than 50 h, and cumulated amounts were lower than 50 mm (Figure 6a,b). Instead, in warm periods, duration and cumulated amounts of the events ranged between 1 and 67 h and between 1.0 and 155.2 mm, respectively. Ninety-five percent of the events had a duration lower than 30 h and cumulated amounts lower than 50 mm (Figure 6a,b).

**Figure 6.** Frequency distribution of duration, cumulated amount, and typology of the rainfall events identified in the period 2000–2018: (**a**) frequency distribution of duration (D) of the rainfall events; (**b**) frequency distribution of cumulated amount (E) of the rainfall events; (**c**) frequency distribution of typology of rainfall events; (**d**) frequency distribution of duration (D) of the rainfall events triggering shallow landslides; (**e**) frequency distribution of cumulated amount (E) of the rainfall events triggering shallow landslides; and (**f**) frequency distribution of typology of rainfall events triggering shallow landslides.

The intensity of the events was classified according to Alpert et al.'s [64] classification. According to the duration and cumulated amount of rainfalls, 87% of the events were classified as light (A), light–moderate (B) or moderate–heavy (C1) (Figure 6c). These events represent the typical rainfalls due to regional frontal systems, which characterize cold months in Northern Italy. Only 13% of the events were heavy (C2) or heavy–torrential (D1) (Figure 6c). Similar results were obtained for warm months, when light (A) and light–moderate (B) were more abundant (Figure 6c). These rainfalls are caused by local convective storms, which are typical of the warm months in Northern Italy. In warm periods, more intense rainfalls were less probable (6% of the total events). Triggering events of shallow landslides occurred more frequently during cold months (Figure 7). Eighty-four percent of the events occurred between January and April and between October and December, with the highest amount in March (20%). Only 16% of landslides triggering occurred in warm months, between May and September, with a higher percentage in August (10%). In cold months, 93% of the total triggering events were light–moderate (B), moderate–heavy (C1), or heavy (C2) rainfalls, with duration between 4 and 105 h and cumulated amount between 30.4 and 133.7 mm (Figure 6d–f). Instead, in warm months, triggering rainfalls were mostly (87%) heavy–torrential (D1) or torrential (D2) rainfalls, characterized by duration between 5 and 15 h and cumulated amounts between 106.8 and 155.2 mm (Figure 6d–f).

**Figure 7.** Distribution of shallow-landslide-triggering events in the period 2000–2018 along the different months of the year (**a**) and cold and warm periods in a year (**b**).
