Temporal Clustering of Precipitation Driving Landslides Over the Italian Territory

The occurrence of multiple precipitation events not‐independent in time, that is, a temporal clustering, is an example of a temporal compounding event. This type of forcing is of great relevance for the occurrence of different natural hazards, like floods and deep‐seated landslides, for which previous soil saturation plays an important role in shaping the associated hazard. Using ERA5‐Land data set and E‐OBS, we firstly investigate the spatial and temporal characteristics of temporal clustering of precipitation over the Italian territory, and we relate it with two oscillation patterns, namely North Atlantic Oscillation (NAO) and Mediterranean Oscillation Index (MOI), and with common synoptic conditions. Then, we explore the role of temporal compounding of precipitation in the generation of different movement types (complex, debris flow, fall, flow, and sliding) using the database of landslides from the Aree Vulnerate Italiane project (in Italian AVI, meaning Areas Affected by Landslides or Floods). From this study it emerges that below average values of NAO and MOI increase the probability of having clustered precipitation events. For all types of landslides, except rock falls, we observed that the majority of the events are preceded by a temporal clustering of precipitation, over longer time windows for complex events, shorter for debris flows. For rock falls, we found also a link with low minimum temperature and freeze‐thaw cycles for winter events and high maximum temperature for summer events. This work contributes to the investigation of temporal clustering of precipitation in connection with natural hazards characterized by a mechanism of saturation. Plain Language Summary Most natural catastrophic events are caused by a sequence in time of multiple not‐independent precipitation events, also called temporal clustering of precipitation. This is related to the process of saturation of the soil that in most cases is not saturated by a single precipitation event. For example, soil moisture is important in the occurrence of landslides, since it causes instability of the slope, or in floods, since it prevents water from infiltrating. When an extreme event is caused or amplified by the occurrence of multiple meteorological events in time or space we talk about climate‐related compound events. In this work we look at the characteristics of temporal clustering of precipitation in Italy, where and when it occurs and its relation with large scale circulations.