Temporal variability of average and low flows in Slovak rivers: A 90-year perspective

Slovakia, Central Europe. This study presents a comprehensive assessment of long-term streamflow variability in Slovakia over a 90-year period (1930/31–2019/20), based on daily discharge data from 27 near-natural catchments. The focus is on trends in average annual flows, 7-day minimum flows, seasonality of low-flow events, and spatial patterns across hydrological regions. This is the first national-scale assessment of Slovak rivers using such a long continuous daily discharge dataset. The analysis reveals a marked spatial gradient in discharge trends: while mountainous regions (Region I) show stable or increasing flow conditions, lowland regions (Region III) experience significant declines — up to 27 % in average annual flow and 23 % in 7-day minimum flows. A strong positive correlation was found between specific discharge and catchment altitude. Notably, despite post-1996 increases in precipitation, runoff decreased due to rising temperatures and evapotranspiration. Minimum flows now occur up to 16 days earlier in lowlands. These results emphasize the unequal hydrological response to climate change across Slovak river basins and provide a solid foundation for future water resource planning under changing climate conditions. • Analyzed 90 years of daily discharge data from 26 Slovak gauges (1931–2020). • Found decreasing trends in annual average flows in southern Slovak rivers. • Specific discharge positively correlated with catchment altitude. • Major dry periods (1934, 1947, 1988–93, 2016–20) identified in low-flow records. • Minimum flow timing advanced by 16 days in lowland rivers in recent decades.