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

Antonio Francipane,Marco Sinagra,Dario Pumo,Goffredo La Loggia,Leonardo Valerio Noto

doi:10.5194/nhess-21-2563-2021

Antonio Francipane, Marco Sinagra + Show 3 more

Open Access

https://doi.org/10.5194/nhess-21-2563-2021

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Abstract

Abstract. In the last few years, some regions of the Mediterranean area have witnessed a progressive increase in extreme events, such as urban and flash floods, as a response to the increasingly frequent and severe extreme rainfall events, which are often exacerbated by the ever-growing urbanization. In such a context, the urban drainage systems may not be sufficient to convey the rainwater, thus increasing the risk deriving from the occurrence of such events. This study focuses on a particularly intense urban flood that occurred in Palermo (Italy) on 15 July 2020; it represents a typical pluvial flood due to extreme rainfall on a complex urban area that many cities have experienced in recent years, especially in the Mediterranean region. 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 stormwater in urban settlements is managed, can be assumed to be a paradigm for modeling pluvial floods in complex urban areas under extreme rainfall conditions. Although the approaches and the related policies cannot be identical for all cities, the modeling framework used here to assess the impacts of the event under study and some conclusive remarks could be easily transferred to other, different urban contexts.

Highlights

During the last few decades, floods and flash floods have reached unprecedented levels in several parts of the globe (Andersson-Sköld and Nyberg, 2016; Gariano and Guzzetti, 2016; Hoeppe, 2016; IPCC, 2019; Jia et al, 2019; Messeri et al, 2015), including the Mediterranean region, where Sicily (Italy) has been one of the most affected areas in between 2008 and 2018 (Trigila and Iadanza, 2018).Sicily is the largest island of the Mediterranean Sea and is characterized by a very complex morphology
The spatial distribution of the topographic index λ was derived from the 2 m resolution digital elevation model (DEM) data of the study area (Fig. 3) with the single flow direction algorithm (SFD; O’Callaghan and Mark, 1984)
This study reproduces the dynamics and impacts of a recent urban flood that affected the city of Palermo (Sicily, Italy), mainly focusing on the analysis of the precipitation event that caused it, which can be classified as an extraordinary event, and the hydrological and hydraulic modeling framework necessary to correctly simulate its effects on rainfall-induced runoff response

Summary

Introduction

During the last few decades, floods and flash floods have reached unprecedented levels in several parts of the globe (Andersson-Sköld and Nyberg, 2016; Gariano and Guzzetti, 2016; Hoeppe, 2016; IPCC, 2019; Jia et al, 2019; Messeri et al, 2015), including the Mediterranean region, where Sicily (Italy) has been one of the most affected areas in between 2008 and 2018 (Trigila and Iadanza, 2018).Sicily is the largest island of the Mediterranean Sea and is characterized by a very complex morphology. The combination of its geographic position, morphology, and climate can lead to the generation of severe rainfall events, especially in between the end of summer and the fall. In the last few years, these rainfall events have become increasingly frequent and severe over the Mediterranean area (Arnone et al, 2013; Cipolla et al, 2020; IPCC, 2019), especially at the subhourly scale (Treppiedi et al, 2021), with a rainfall–runoff response often exacerbated by the ever-growing urbanization (Arnone et al, 2018; Easterling et al, 2000; Pumo et al, 2017). In recent times, some intense rainfall events have caused urban floods and flash floods in many cities of the island, with consequent economic damages and, sometimes, loss of human life.

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