Long-term analysis of changes in seasonal and maximum discharges of Slovak rivers in the period 1931–2020

Abstract Central Europe and other parts of the world have experienced numerous extreme floods and prolonged periods of very low water discharges. With the increasing length and availability of hydrological data time series, it is now possible to analyse a larger volume of data. This paper presents long-term of changes in seasonal and maximum discharges. This paper aims to comprehensively assess the hydrological regime changes of Slovak rivers, using data from 26 gauging stations based on 90 years of observation. The study’s first part explores monthly flow changes within each year for selected Slovak rivers. The second part identifies changes in the maximum daily discharges, their long-term trends, and their occurrences. Additionally, we have compared the variability of the hydrological regime of the Slovak rivers with the variability of the hydrological regime of selected gauging stations on the Danube River and its tributaries, such as the Drava, Sajó, and Tisa rivers, to understand broader regional patterns. The findings show that the rivers selected exhibit relatively high intra-annual runoff variability, with various changes in the runoff regime curve based on the long-term monthly Pardé coefficient. For the Slovak region, maximum annual runoff variability is observed in the Krupinica and Plašťovce rivers (reaching a maximum of 12.1 during the period 1930–1960), while minimum annual runoff variability is observed in the Biely Váh River (2.205 for the period 1930–1960). The long-term trend analysis of the Burn index time series for maximum daily discharges over the entire period from 1930/31 to 2019/20, as well as the significance of trends during the summer-autumn and winter-spring seasons, shows that stations exhibited decreasing, stable, or increasing trends. The most significant increasing trend was observed at sixteen of the stations analyzed: at seventeen stations during the summer-autumn season and at nine stations during the winter-spring season over the period from 1930/31 to 2019/20.