engleski

Hydro-meteorological analysis of summer 2020 urban flood in Zagreb

Extreme weather situations are of great interest due to their damaging effect on society, ecosystem, infrastructure, etc. In a world with a changing climate, increase in occurrence and intensity of such events might be expected. In this study, extreme precipitation event on 24 July 2020 which resulted in urban flood in Zagreb area, is analyzed from hydro-meteorological point of view. First, a general climatology of the short-term (from 5 to 120 min) extreme precipitation amount is analyzed in terms of its timing and correlation with other durations for the Zagreb-Griĉ station in the period 1908–2020. Temporal changes in the amplitude of extreme precipitation are examined by trend analysis, as well as non-stationary generalized extreme value distribution (GEV). Trend results revealed an intensification in short-term extreme precipitation up to 2.9% per 10 years, which is significant for durations longer than 20 min. Together with the results of analysis of occurrence and correlogram analysis, these findings point to changes in the occurrence of corresponding weather types responsible for heavy rainfall events. Summer 2020 rainfall event analysis showed that 120-min extreme precipitation was an exceptional event over the city center with return period higher than 100 years. All available data, measurements and numerical weather prediction models revealed that all ingredients for deep moist convection were present before the event, together with a deep layer shear. Additionally, the formation of cutoff low, the presence of an intense positive potential vorticity anomaly and the surface convergence line appear to be the main processes which further enhanced triggered deep convection, consequently also heavy precipitation. The hydrological analysis revealed that the sewerage system of Zagreb city could not drain the stormwater from the streets, pointing out the need for its redesign and adaptation to climate change. The results obtained from this study might serve for better preparedness of the city and society to future similar events.

Extreme short-term precipitation, urban flood

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