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Timing of floods; Seasonality; Circular kernel density histograms; Trends in flood magnitude, Climate change
Abstract:
This study compares the flood regime of rivers in Ukraine and Austria over the last decades. We used data from mountain and lowland watersheds, where floods are caused by different processes. In order to identify possible shifts in the day of occurrence of annual flood maxima, we apply the kernel density method to the time series of two subperiods (1960–1987 and 1988–2015). We use the Mann Kendall test at a 5% significance level to identify significant positive or negative trends in the series of annual maximum discharges. In Austria, we observe an increasing trend in summer floods associated with increasing precipitation. In the lowland areas of Ukraine, a clear reduction in spring floods is observed, linked to shallower snow packs in a warming climate. In the Ukrainian Carpathians, on the other hand, where floods occur throughout the year, an increase in the portion of liquid precipitation during the cold period of the year leads to earlier floods and an increase in the probability of flooding in winter.
