Riverine flood risk in municipalities of Slovakia

Integrated flood risk assessment is based on a multidimensional definition of flood risk, i.e. the extent of flood losses depends not only on the flood hazard itself, but also on the vulnerability of the social, economic, and environmental system to flooding. This study aims at the riverine flood risk mapping and assessment in municipalities of Slovakia. The riverine flood risk index (RFRI) was determined for 2,927 municipalities of Slovakia as a synthesis of the riverine flood hazard index (RFHI) and the riverine flood vulnerability index (RFVI) using the spatial multi-criteria analysis and geographic information systems (GIS). The RFHI was calculated based on eight indicators representing the riverine flood potential: number of flood events, slope, curvature, average annual maximum 5-day rainfall, river density, lithological rock types, soil texture, and land cover. Moreover, the RFVI was calculated based on seven indicators representing the social and economic vulnerability of municipalities: population density of urban areas of municipalities, share of population included in the age category 65+ from the total population of municipality, share of unemployed persons from the total number of economically active population in municipality, share of the Roma ethnicity from the total population of municipality, number of buildings within 100 m from a river, length of roads within 100 m from a river, and number of bridges in a municipality. The result of the Pearson correlation between individual indicators and the number of flood events in municipalities was used to determine the importance of indicators, which was subsequently used for assigning the indicator weights applying the rank sum method. The RFHI and RFVI for each municipality were calculated as the aggregation of the respective weighted indicators. The multiplication of the RFHI and RFVI resulted in the final RFRI. Based on the results obtained, the very high and high classes of RFHI contained 839 municipalities, which are located mostly in northern and eastern Slovakia and partly also in western and central Slovakia. The very high and high classes of RFVI included 817 municipalities, mainly, in northern and central Slovakia and partly also in western and eastern Slovakia. The highest RFRI values were recorded mostly by the municipalities in northern, central, and eastern Slovakia and partly also in western Slovakia. The very high and high risk of riverine flooding was recorded in 700 municipalities, i.e. these municipalities are included in the very high and high classes of RFRI. The results achieved in this study are useful, on one hand, for local self-governments and actors responsible for flood risk management, but more importantly for cyclic updating of the Preliminary Flood Risk Assessment in Slovakia under the EU Floods Directive. This work was supported by the VEGA agency under the grant number 1/0103/22 through the project entitled "Spatio-temporal Changes and Prediction of Flood Risk in Municipalities of Slovakia".