Characterization of the November 2020 damaging hydrogeological event affecting the Calabria region (southern Italy)

Abstract Damaging hydrogeological events (DHEs), characterized by concurrent phenomena such as floods and landslides triggered by rainfall, pose significant threats to people and properties. Calabria, in southern Italy, frequently experiences these events, which lead to substantial economic losses in agriculture and severe damage to transport infrastructure. Addressing DHEs is crucial, especially considering climate change, which is expected to increase their frequency and intensity. This paper examines the DHE that occurred between November 20th and 22nd, 2020, on the eastern side of Calabria. To evaluate the event’s severity, two indices were applied: one measuring the exceptional nature of the triggering rainfall and the other assessing the severity of damage to people and property. By comparing these indices to historical DHEs data from the early twentieth century onward, the 2020 event has been classified as an “extraordinary event” for its very high rainfall severity and moderately high damage levels. In fact, during the event there were no fatalities or injuries and the damages were relatively manageable and recoverable with moderate expenses. In addition, to study whether the meteorological framework of the event can be traced back to those characterizing major DHEs, a detailed synoptic analysis was carried out. As a result, the meteorological conditions were identified as quite common in Calabria during autumnal DHEs (e.g., 1921, 1953, 1959, and 1971), resulting from the descent of Atlantic troughs into the Mediterranean and leading to the formation of surface minima that channel high-humidity air masses from the south, thus enhancing convective phenomena. The applied methodology, outlined in previous studies, is applicable in regions like Calabria, where historical DHEs have been systematically analysed and categorized based on rainfall and damage severity, providing a basis for comparison. Moreover, the synoptic analysis supplies new key elements to identify meteorological conditions driving to damaging events in the study region that can be useful to improve preparedness and emergency management during future DHEs.