Aim of the study:
The aim of this study is to assess the vulnerability of municipalities located in the Gidra River Basin to fluvial floods. We have calculated a fluvial flood vulnerability index (FFVI) related to the year 2021 for twelve municipalities, which fall into the Gidra River Basin and whose urban area is completely or partially located in the basin, and at the same time a watercourse, belonging to the Gidra River Basin, flows through the municipality.

Material and methods:
Three indicators (number of buildings within a 100 m radius from the watercourse; length of roads within a 100 m radius from the watercourse; and number of bridges over a watercourse) representing the economic vulnerability, and seven indicators of social vulnerability (population density of municipalities; share of residents aged 65+ in the total number of residents; share of unemployed residents in the total number of economically active residents; share of households with six and more persons in the total number of households; share of incomplete households in the total number of households; share of residents without education and with primary education in the the total number of residents; and share of residents with disabilities in the total number of residents) were used to determine the respective economic flood vulnerability sub-index (EFVsI) and social flood vulnerability sub-index (SFVsI). We normalized the original values of indicators using the maximum method and treated all of the indicators as equally important. In the last step, we determined the FFVI for each municipality at a scale [0, 1] by an aggregation of the EFVsI and SFVsI, which both had equal weights.

Results and conclusions:
The highest values of the EFVsI were recorded in the municipalities of Častá (0.81), Cífer (0.66), and Budmerice (0.64), which are located in central (Cífer) and upper (Častá and Budmerice) parts of the basin. The highest values of SFVsI were recorded in the municipalities of Píla (0.79) and Štefanová (0.76), which are both located in the upper part of the basin. Based on the values of the final FFVI, we can conclude that the highest vulnerability to fluvial floods is found in the municipalities of Častá (0.75), Budmerice (0.67), and Cífer (0.67). On the contrary, the lowest values have been recorded in the municipalities of Ružindol (0.37), Pavlice (0.38), and Jablonec (0.40). The results of this study can be useful for determining the overall flood risk, which is a synthesis of the hazard and vulnerability components. This task is planned for the future research in the study area.