What if the 25 October 2011 event that struck Cinque Terre (Liguria) had happened in Genoa, Italy? Flooding scenarios, hazard mapping and damage estimation

Abstract

Abstract. During the autumn of 2011 two catastrophic, very intense rainfall events affected two different parts of the Liguria Region of Italy causing various flash floods. The first occurred in October and the second at the beginning of November. Both the events were characterized by very high rainfall intensities (> 100 mm h−1) that persisted on a small portion of territory causing local huge rainfall accumulations (> 400 mm 6 h−1). Two main considerations were made in order to set up this work. The first consideration is that various studies demonstrated that the two events had a similar genesis and similar triggering elements. The second very evident and coarse concern is that two main elements are needed to have a flash flood: a very intense and localized rainfall event and a catchment (or a group of catchments) to be affected. Starting from these assumptions we did the exercise of mixing the two flash flood ingredients by putting the rainfall field of the first event on the main catchment struck by the second event, which has its mouth in the biggest city of the Liguria Region: Genoa. A complete framework was set up to quantitatively carry out a “what if” experiment with the aim of evaluating the possible damages associated with this event. A probabilistic rainfall downscaling model was used to generate possible rainfall scenarios maintaining the main characteristics of the observed rainfall fields while a hydrological model transformed these rainfall scenarios in streamflow scenarios. A subset of streamflow scenarios is then used as input to a 2-D hydraulic model to estimate the hazard maps, and finally a proper methodology is applied for damage estimation. This leads to the estimation of the potential economic losses and of the risk level for the people that stay in the affected area. The results are interesting, surprising and in a way worrying: a rare but not impossible event (it occurred about 50 km away from Genoa) would have caused huge damages estimated between 120 and EUR 230 million for the affected part of the city of Genoa, Italy, and more than 17 000 potentially affected people.

Quantification of flood risk mitigation benefits: A building-scale damage assessment through the RASOR platform

“…A supplementary material). This approach has been already described in Silvestro et al (2016). surveys showing a good agreement between simulated and recorded flood losses (Trasforini et al, 2015).…”

“…Unfortunately for the presented case study such data are not available. However, the damage curves libraries of the RASOR platform performed very well in another italian case study when compared to citizen claims and municipal authorities surveys, thus the model 85 is considered reliable at least for comparing several scenarios in the study area (Silvestro et al, 2016;Trasforini et al, 2015). In order to answer the common stakeholders' question "How much should I invest to achieve the desired residual risk?"…”

“…Replacement costs account for market values, census data and insurance data to properly describe urban spatial variability. Damage calculations are carried out within the RASOR platform (Silvestro et al, 2016;Rudari and RASOR TEAM, 2015;Koudogbo et al, 2014). It is widely acknowledged 80 that a flood damage estimation without validation against local historical loss data may sound weak (Ballio et al, 2015).…”

Ensemble cloud-resolving modelling of a historic back-building mesoscale convective system over Liguria: the San Fruttuoso case of 1915

“…Such a scenario has often been observed in the last decade, when Liguria (NW Italy) and southern France have been repeatedly hit by severe floods: 2010 Varazze andSestri Ponente, 2011 Cinque Terre andGenoa, 2012 Marseille and Isle du Levant, 2014 Genoa andChiavari, 2015 Nice. As shown in several recent works (Parodi et al, 2012;Rebora et al, 2013;Fiori et al, 2014;Duffourg et al, 2015;Silvestro et al, 2015;Cassola et al, 2016;Silvestro et al, 2016), convective cells, embedded in such MCSs, are generated on the sea by the convergence of a warm and moist south-easterly flow and a northerly much colder and drier one. These structures are then advected to the land where the combined action of the aforementioned currents and the topography force them to persist for several hours over a very localized area (e.g.…”

Effects of digital terrain model uncertainties on high‐resolution urban flood damage assessment

“…The open source code Telemac-2D for 2D hydrodynamic simulation (Hervouet, 2007) and the Rapid Analysis and Spatialisation Of Risk (RASOR) open platform for damage assessment Silvestro et al, 2016) are used in the study. Four high-resolution DTMs with increasing preprocessing are used to run 2D hydrodynamic simulations and damage model for assigned test hazard scenarios.…”