## 2 Methods
Performing a multi-criteria analysis for the assessment of the spatial units of a city, in terms of their vulnerability to hydrological risks, requires the following steps:  
* Division of the city area into spatial units;
* Selection of assessment criteria;
* Collection of data for the calculation of criterion values;
* Selection of weights for individual criteria;
* Calculation of criterion values and their normalised values;
* Calculating the products of the normalised criterion values and the weights of a criterion;
* Calculating the sum of the products and performing the ranking of the spatial units;
* Drawing up a table and map composition. In Table 1, the criteria taken into account for a multicriteria analysis focusing on hydrological threats have been included. The choice of criteria was based on expert knowledge of the most important factors affecting urban water runoff and retention within the city, as well as the availability of data. Some data, such as digital maps of combined or rainwater networks, were not accessible for certain cities. Additionally, parameters obtained during the project, such as the average runoff value, were considered in the selection process. The main advantages of the adapted multi-criteria method lie in its site-specific nature and flexibility. Experts and stakeholders can determine the most relevant parameters influencing urban water management based on local conditions, ensuring that the analysis is tailored to the unique hydrological and environmental challenges of each city. This method effectively integrates diverse spatial datasets, including historical flood records, GIS-based environmental indicators, and urban infrastructure data, to provide a comprehensive assessment. Ultimately, it identifies the most vulnerable areas where immediate action is required or where changes in land use are inevitable. By combining expert knowledge with data-driven insights, the approach supports informed decision-making, prioritising interventions that enhance urban resilience and sustainable water management. However, the choice of criteria significantly influences the ranking of vulnerability. If key factors such as soil permeability, drainage infrastructure, or socio-economic resilience are omitted, \begin{table}
\begin{tabular}{c c c} \hline
**ID** & **Criterion** & **Unit** \\ \hline
1 & Average intensity of soil sealing on spatial unit for instance city district & [\%] \\
2 & Average soil sealing & [\%] \\
3 & Percentage of areas that were affected by 100-year flooding & [\%] \\
4 & Area of buildings in the range of 100-year flood & [m\({}^{2}\)] \\
5 & Retention potential factor (biologically active areas) & [\%] \\
6 & Average run-off resulting from 1\% chance rainfall & [mm] \\
7 & Percentage of areas covered by non-drained areas & [\%] \\
8 & Percentage of areas covered by buildings adjacent to non-drained areas & [\%] \\
9 & Area of streets prone to flooding & [m\({}^{2}\)] \\
10 & Area covered by local flooding & [m\({}^{2}\)] \\
11 & Length of flooded streets & [m] \\
12 & Number of local floods on spatial unit for instance city district & [-] \\
13 & Number of manholes on spatial unit for instance city district & [-] \\
14 & Length the drainage network pipes & [m] \\ \hline \end{tabular}
\end{table} 
Table 1: Criteria for multi-criteria analysis of flood risks. the analysis may provide an incomplete picture. Conversely, including too many criteria can introduce redundancy and dilute the impact of critical factors. Additionally, assigning weights to criteria is a process based on expert or stakeholder judgment, making the analysis inherently subjective. Different stakeholders may prioritise certain factors over others, leading to variations in the assessment outcomes. Critical to the multi-criteria analysis was the estimation of the weight of the criterion, which was averaged based on the judgement of the water group experts. It is essential to highlight that the data utilised for the analyses were freely available.