Assessment of severity levels of Damaging Hydrogeological Events in Calabria (Southern Italy)

A Rainfall Event and a subsequent Damage Event, resulting from floods and landslides triggered by rainfall, are the two components which characterize a Damaging Hydrogeological Event (DHE). Since the same rainfall amount can cause different degrees of damage, depending on both rivers and slopes conditions, both Rainfall and Damage Event characteristics are related to climatic, geomorphological and anthropogenic factors. Moreover, as to what concerns the damage, and specifically the damage occurrence, this also depends on the geographical distribution of damageable elements such as population, lifelines and urbanized sectors. In this paper, a methodology for the classification of the severity of the DHEs, which have been recorded in a region of southern Italy (Calabria), is proposed. The applied methodology was based on a chart which considers some indicators of both the Damage (Dscore) and the daily Rainfall values (Rscore) recorded in the study area; the chart was applied to a series of 30 DHEs which occurred between 1981 and 2010. As a result, four types of events have been identified: ordinary events, obtained by low Dscore and Rscore values; extraordinary events, with high Rscore values but low Dscore values; catastrophic events, characterized by non-exceptional rainfall (low Rscore) and severe damage (high Dscore); major catastrophic events, having high Dscore and Rscore values. Given that, media accounts and first or second-hand personal accounts fail to provide an objective classification, the aim of this study was to provide an objective classification of the severity of the DHEs through the production of a chart.