Characteristics of the landslides triggered by the extraordinary rainfall event occurred in Central Italy on September 15, 2022

Timely and systematic collection of landslide information after a triggering event is essential for the definition of landslide trends in response to climate change. On September 15, 2022 Marche and Umbria regions, in Central Italy, were struck by an anomalous rainfall event that showed characteristics of a persistent convective system. An extraordinary cumulated rainfall of 419 mm was recorded by a rain gauge in the area in only 9 hours. It was carried out a systematic reconnaissance field survey to prepare an event landslide inventory map in an area of 550 km2 that includes a large neighbourhood of the area that recorded the highest rainfall intensity. The rainfall triggered 1687 landslides in the area affected by the peak rainfall intensity. Landslide area spans from a few tens of square meters to 105 m2, with a median value of 87 m2. We describe the characteristics of the landslides identified during a field survey conducted immediately after the event. Most of the mass movements are shallow, many are rapid (i.e., debris flows, earth flows) and widely affecting the road network. Many national and local roads were interrupted, mostly by earth and rock slides; national and local railways were interrupted at several points; extensive damage was registered to structures and infrastructures. Furthermore, field evidence revealed that a vast proportion of landslides occurred in the immediate vicinity of roads, mostly affecting road embankments and that a large number of landslides initiated within natural and semi-natural areas and hit the road network and, locally, affected houses and activities. Field surveys also revealed diffuse residual risk conditions, being a large proportion of landslides located in the immediate vicinity of infrastructures. Besides reporting the spatial distribution of landslides triggered by an extreme rainfall event, the data collected on landslides can be used to make comparisons with the distribution of landslides in the past, validation of landslide susceptibility models, definition of the general interaction between landslides and structures/infrastructures.