## 2 Materials and Methods  
### Geographical Context and Single Risk Description  
To introduce the concept of multi-risk assessment, it is first necessary to discuss the concept of single risk. Risk is basically defined as the product of three parameters: Hazard, vulnerability, and exposure [9]. A hazard represents the probability that an adverse event will occur in a specific area and in a specific time interval. Vulnerability, on the other hand, is an intrinsic characteristic of a system; it represents its propensity to suffer a certain level of damage following the occurrence of a hazard event. Finally, exposure indicates the presence of people, critical infrastructures, natural and cultural heritage, and much more still in hazard zones that are thereby subject to potential losses [4]. The concept of multi-risk follows as the overall risk from a multi-hazard and multi-vulnerability perspective. The term multi-hazard indicates several hazards affecting the same exposed elements (with or without space-time coincidence) or the occurrence of a hazard event that triggers another one giving rise to a domino or cascade effect. Furthermore, the term multi-vulnerability indicates those circumstances where several elements are sensitive to different possible vulnerabilities towards the various hazards affecting them or vulnerabilities that vary over time [10; 11]. The territory of the province of Ferrara is located at the north-eastern extremity of the Padana Plain, a flat land area in the north part of Italy crossed by the Po River and bathed by the Adriatic Sea on the east side. It is characterized by minimum land slopes and its altimetry is mainly under the mean sea level, as almost half of its area is below the mean sea level, as shown in Figure 1. Moreover, the eastern part of the territory is affected by subsidence phenomena as well. These ground-level modifications, caused mainly by anthropogenic actions as well as by geological and neotectonic factors [31; 32], produced a subsidence rate of up to \(-2.5\) mm/year [31]. The main watercourses that flow through the Ferrara province are the Po River, which marks the northern border of the Reno River, and the Idice and Sillaro streams, which are not tributaries of the Po River, and cross the province in their last stretch. Furthermore, numerous artificial canals flow through the Ferrara Province, including the Cavo Napoleonico, which connects the Po and Reno rivers, and the Idrovia Ferrarese. The province of Ferrara includes 23 municipalities. Attention is hereafter restricted to the two main risks of the area under study, namely flood and seismic risks. Site effects associated with inherent geological morphology and instability issues such as liquefaction  
Figure 1: Altimetric map of Ferrara province (free source [[https://www.bonificaferrara.it/images/Allegati/SfTL/4d-3-altimetria](https://www.bonificaferrara.it/images/Allegati/SfTL/4d-3-altimetria)]([https://www.bonificaferrara.it/images/Allegati/SfTL/4d-3-altimetria](https://www.bonificaferrara.it/images/Allegati/SfTL/4d-3-altimetria))(100).pdf, accessed on 3 January 2022, made available by Consorzio di Bonifica Pianura di Ferrara). The minimum and maximum extremal values of the ground level over the sea in the legend are \(-2\) m (dark blue) and \(60\) m (dark red), respectively. were not considered, for simplicity. Desertification is another risk that has been emerging in recent years in the Po delta plain [10]. However, it has not been considered in the present contribution. Hereafter, flood risk refers to the risk that depends on the probability of occurrence of a flood, evaluated concerning the different typologies of watercourses that flow through the territory. The flood risk for the selected region was quantified by the Land Reclamation Authority of the province of Ferrara (Consorzio di Bonifica Pianura di Ferrara), and accounts for flood hazard, exposure, and vulnerability parameters.