## 2 Materials and Methods
### Data Collection and Processing  
Both flood and seismic risks have been included in PROMETHEE as criteria according to their components (hazard, exposure, and vulnerability), while the municipalities, i.e., the object on which to evaluate the criteria, are the alternatives. Risk parameters for each municipality are made available by the National Institute of Vulcanology and Geophysics (INGV), the Italian National Institute of Statistics (Istat), and the Land Reclamation Authorities of the Province of Ferrara. Accordingly, we have drawn from the aforementioned databases a simplified map of the flood risk. In particular, Figure 3 displays the flood hazard for the Province of Ferrara in terms of the probability of floods. In this map, the classification is based on Italian Government Decree n. 49/2010 [35]. Accordingly, frequent floods are defined as those having a high probability of occurrence, with a return period of \(20\leq\text{T}\leq 50\) years (P3); infrequent floods have an average probability of occurrence with a return period of \(100\leq\text{T}\leq 200\) years (P2); finally, low-probability floods have a return period of \(200<\text{T}\leq 500\) years (P1).  
Figure 4 provides a map of the seismic hazard for the province of Ferrara in terms of peak ground acceleration (PGA). The PGA-intervals are indicated in the legend.  
As for exposure-related criteria, for each municipality, we adopted three parameters: Land use percentage, the number of strategic buildings, and population density. All of them  
Figure 4: Map of the seismic hazard for the province of Ferrara in terms of peak ground acceleration.  
Figure 3: Map of the flood hazard for the province of Ferrara in terms of probability of flood.  
were drawn from the Istat database. The strategic buildings were defined based on the presence and number of halls, police stations, fire brigade buildings, schools, universities, water, lifting plants, hospitals, and civil protection centers. This information was obtained from the website of the province of Ferrara ([[http://www.provincia.fe.it/](http://www.provincia.fe.it/)]([http://www.provincia.fe.it/](http://www.provincia.fe.it/)), 1 October 2021), as per educational and public institutions and centers, and from the website of the Consorzio di Bonifica Pianura di Ferrara as per water lifting plants ([[https://www.bonificaferrara.it/](https://www.bonificaferrara.it/)]([https://www.bonificaferrara.it/](https://www.bonificaferrara.it/)), 1 October 2021).  
Specifically, four classes of land use percentages were obtained based on the ratio between the urbanized area divided by the total area. In synthesis, we collected the municipalities into four land use classes (Figure 5), four classes in terms of the number of strategic buildings (Figure 6), and four classes of population density (Figure 7).  
As for the vulnerability criteria, we adopted a single non-dimensionalized parameter, which accounts for the average age of buildings. Knowing the age of construction and the corresponding number of buildings, we computed the following vulnerability index:  
\[I_{v}=\frac{A\ \alpha_{1}+B\ \alpha_{2}+C\ \alpha_{3}+D\ \alpha_{4}}{A+B+C+D}\,\]  
where \(A,\ B,\ C\ e\ D\) represent the number of buildings built between the end of 1800 and 1945; the number of buildings built between 1946 and 1980; the number of buildings built between 1981 and 2000, and finally, the number of buildings built from 2001 up to now. \(\alpha_{1},\ \ a_{2},\ \ a_{3}\ e\ \alpha_{4}\) are coefficients equal to 1, 0.75, 0.5, and 0.25, respectively. The vulnerability index I\({}_{v}\) results in being mainly related to the age of buildings, and its map is shown in Figure 8.  
Figure 5: Land use map for the province of Ferrara.  
Figure 6: Map of strategic buildings incidence for the province of Ferrara.  
Figure 7: Map of the population density for the province of Ferrara.