A paradigm of extreme rainfall pluvial floods in complex urban areas: the flood event of 15 July 2020 in Palermo (Italy)

In the last years, some regions of the Mediterranean area are witnessing a progressive increase in extreme events, such as urban and flash floods, as a response to the increasingly frequent and severe extreme rainfall events and their ground effects, which are often exacerbated by ever-growing urbanization. In such a context, the traditional defense of urban areas, which are usually based on urban drainage systems designed without regard to the impacts of urbanization and climate change on natural systems, may not be sufficient to deal with the risk deriving from the occurrence of such events. This study focuses on a very recent and particularly intense urban flood that occurred in Palermo on 15 July 2020 that represents a perfect example of extreme rainfall pluvial floods in a complex urban area that many cities, especially in the Mediterranean region, have been experiencing in recent years. A conceptual hydrological model and a 2D hydraulic model, particularly suitable for simulations in a very complex urban context, have been used to simulate the event. Results have been qualitatively validated by means of crowdsourced information and satellite images. The experience of Palermo, which has highlighted the urgent need for a shift in the way of managing stormwater in urban settlements, can be assumed as a paradigm of management of extreme rainfall pluvial floods in complex urban areas. Although the approaches and the related policies cannot be identical for all cities, the modeling framework here used to assess the impacts of the event under study and some conclusive remarks could be easily transferred to other and different urban contexts.