engleski

Rainfall thresholds related to pluvial flooding in urban areas – case study in the city of Zagreb, Croatia

The frequency of urban pluvial flood risk has increased in recent years due to changes in the hydrological cycle and more frequent extreme rainfall events. Therefore, the analysis of rainfall tresholds trelated to pluvial urban flooding could be of great help to improve early warning systems and enable public services to plan and implement appropriate protection and rescue measures in a timely manner. The aim of this paper is to identify preliminary rainfall thresholds for different durations up to 24 hours that are related to urban floods in the city of Zagreb, Maksimir area, in the period 2007-2017. Reports from civil protection and public fire brigades of the city of Zagreb were analyzed, i.e. technical interventions for pumping water from facilities and open urban spaces during extreme hydrometeorological conditions were considered and used as impact parameters of pluvial floods. A spatial analysis was performed and a relationship was established between urban land use and the number of interventions as an indicator of flood occurrence. Total precipitation measured at Maksimir meteorological station was analyzed and maximum values for 1, 2, 3, 6, 12 and 24 hours durations were determined, and were used as flood hazard indicator. Rainfall events were analyzed using an empirical approach and extended with a statistical approach to develop rainfall thresholds, and the performance of both approaches was evaluated. The results showed that most interventions occurred during the warm season (especially in May and August). Both thresholds obtained, the empirical and the statistical, could be used for practical purposes. However, the upper statistical threshold (75% percentile) has sufficient overall correctness with more correct flood predictions and higher false alarm rates than the upper empirical threshold, while the lower statistical threshold (25% percentile) has slightly better correctness than the lower empirical threshold.

Urban floods ; Interventions ; Precipitation ; Threshold values

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