Abstract
Studying the changes in extreme river runoff induced by climate change is of utmost importance, as the variability of floods directly affects life and human activities. This study examines the fluctuations and persistence of winter floods in 14 catchments in the Rika River Basin (Ukraine) and ten catchments in the Steyr River Basin (Austria). The catchments represent typical hydrological regimes in the Danube River region. The fluctuations and persistence of floods are analyzed by the hydro-genetic method and a seasonality analysis for the period 1951–2015. The results show a much more pronounced fluctuation pattern in the upper Rika catchments than in the upper Steyr catchments. This pattern indicates an increase in winter flood magnitudes between the mid-1960s and the 1990s, followed by a decrease until recently. The flood seasonality shows a large inter-annual variability in both regions. The most significant winter floods tend to occur in November and December. The winter flood fluctuations are compared with changes in associated climate characteristics, i.e., seven-day maximum precipitation, a melt index, and annual maximum snow depth. The seasonality of these characteristics has a strong inter-annual variability and only partly explains the winter flood fluctuations.
Highlights
With recent climate changes, many regions are observing modifications and fluctuations in extreme hydrological events, such as floods
The results show a distinct difference between the Austrian and Ukrainian parts of the Danube River basin fluctuations
While the magnitude and length of the cycles in Austrian catchments is smaller, most of the Ukrainian catchments show a distinct fluctuation pattern consisting of an increasing phase of winter flood magnitude from the mid-1960s until the end of the 1980s, followed by a decrease until the recent period (2015)
Summary
Many regions are observing modifications and fluctuations in extreme hydrological events, such as floods. Recent studies attribute the differences in seasonality and magnitude of floods to changes in autumn and winter precipitation, decreasing evaporation or snow cover, and snowmelt [1,2]. Due to recent climatic warming, changes in the timing of snow accumulation and melt are observed mainly in northeastern and eastern Europe and in mountain regions [3]. Recent analyses in Eastern Europe [4,5] indicate a simultaneous increase in number of winter floods as a result of thawing and a general increase in winter flow volumes. The changes in snow cover are known to affect the hydrological regime and floods, but how this effect varies between regions is still not well understood. Understanding the factors that control timing, magnitude, and changes of floods is essential for design, water resources, and flood
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