# Methodology for the Assessment of Multi-Hazard Risk in Urban Homogeneous Zones
## 2 Methodology
### Risk Assessment of Buildings  
In this research, the risk assessment is made for different levels, starting from the lowest level (micro level), i.e., an individual building. At this micro level, the risk assessment of a single-hazard exposure is based on the calculation of vulnerability indexes of buildings for individual natural disasters:  
- Flood vulnerability index for buildings,  
- Extreme coastal waves vulnerability index for buildings,  
- Seismic vulnerability index for buildings,  
as well as on assessment of the single hazards:  
- Flood hazard,  
- Extreme coastal waves hazard,  
- Seismic hazard. Seismic vulnerability indexes of the buildings for investigated area are calculated according to the seismic vulnerability method [35]. The method is based on the evaluation of 11 geometrical, structural and non-structural vulnerability parameters of the building. They consider the influence of the type and quality of the structural system, the shear resistance in two horizontal directions, the position and the foundations, the properties of floors, the configuration in plan and elevation, the maximum wall spacing, the roof's topology and weight, the existence of non-structural elements, and the state of preservation. Four possibilities for each parameter were decided: from \"A\", indicating an optimal state, to \"D\", indicating a poor state. The relative importance of each parameter in the overall vulnerability is computed by using weight coefficients relating to each parameter. Finally, the vulnerability index \(\mathrm{I}_{\mathrm{v}}\) is calculated in a form \(\mathrm{I}_{\mathrm{V}}=\sum_{\mathrm{i}}\mathrm{s}_{\mathrm{vi}}\mathrm{w}_ {\mathrm{i}}\), where \(\mathrm{s}_{\mathrm{vi}}\) is the numerical score for each class, and \(\mathrm{w}_{\mathrm{i}}\) is the weight of each parameter. The vulnerability index is normalized in a 0-100% range; a low index indicates high seismic resistance and low vulnerability, while a high vulnerability index is characteristic of the buildings with low seismic resistance and high vulnerability. Vulnerability indexes of the buildings located in the pilot area are presented in Figure 5 [35]. Figure 4: The scheme of the risk assessment for investigated area: (**a**) single-hazard exposure; (**b**) multi-hazard exposure. The flood vulnerability index and the extreme coastal waves vulnerability index are calculated according to the methodology developed in the PMO-GATE project [25]. This methodology is based on the approach of [PERSON] and [PERSON] [36], which takes into consideration different parameters such as building material, overall object condition, number of storeys, building age, importance of exposed objects and level of exposure. The approach has been modified for application in the multicriteria analysis, with each vulnerability index calculated as the weighted sum of set of parameters and evaluated through vulnerability classes (Figure 6). Figure 5: Seismic vulnerability index of buildings divided into 10% intervals. Figure 6: _Cont._  
The seismic hazard for Croatia is presented with two maps for return periods of 475 and 95 years, expressed in terms of the peak ground acceleration during an earthquake for a soil class A [37]. According to HRN EN 1998-1:2011 [36], the soil types A, B, C, D and E, may be used to account for the influence of local ground conditions on the seismic action. The site can be classified according to the value of the average shear wave velocity \(\rm{v_{s,30}}\). An investigation of the deep geology and characteristics of the terrains, performed at pilot area [38], has shown that shear wave velocity \(\rm{v_{s,30}}\) is higher than 800 m/s at the wholearea, which define soil class A. Therefore, local ground conditions do not influence to seismic hazard in the investigated area, i.e., the seismic hazard for all buildings at the pilot area has been assumed to be constant [35].