Flood and Landslide Damage in a Mediterranean Region: Identification of Descriptive Rainfall Indices Using a 40-Year Historical Series

In the future, as a result of global warming, it is possible that rainfall could becomemore intense and frequent. This could lead to more frequent triggering of damaging phenomenasuch as floods and landslides (named as a whole damaging hydrogeological events, DHE), and,consequently, to the increase of their impacts on territories, especially in regions where uncontrolledurban sprawl represents a factor that can exacerbate the problem. The analysis of a large quantityof information about both triggering rainfall and triggered phenomena can help to comprehendrelationships between triggering precipitation and its related impacts. In this paper, to facilitatethe investigation of the relationships between large and complex datasets concerning both rainfalland rainfall-related damage, we propose an index-based approach, illustrated by its applicationto the Calabria region (Southern Italy). In particular, this manuscript presents some results from apreliminary investigation aimed at assessing the "better" index to describe DHE. Five rainfall indices(RIs) were tested and five composite rainfall indices (CRIs), combinations of two or more RIs, areproposed. We calculated the RIs and the CRIs by means of 1,300,000 daily data registered in theobservation period 1980-2020. The CRIs showed the best relationships with the data of damaginghydrogeological events (DHEs). Particularly, better results were obtained with landslides data thanwith floods data, perhaps due to the hydraulic characteristics of the Calabria rivers, affected by flashfloods mainly influenced by very intense hourly rainfall events.