Shifting seasonality of runoff extremes in headwaters of the Krkonoše National Park

This study examines the runoff seasonality, focusing on low-flow and high-flow events in five headwater catchments of the Krkonoše (Giant Mts.) National Park, Czechia over the 1964–2023 period. The research aims to quantify the timing, distribution, and trends of streamflow extremes in order to understand the impact of climate change on hydrological dynamics in this protected area. The results show significant shifts in runoff seasonality. Low-flow events are increasingly clustered in late summer and early autumn, occurring several weeks earlier in most catchments. High-flow events have moved earlier in spring, driven by changes in the timing of snowmelt due to rising temperatures and decreasing winter snowpack. Analysis of the seasonality index shows an increase in the regularity of both low and high flows across in all study catchments. Statistical tests identified significant decreases in both minimum and maximum streamflow, particularly for annual 7-day and 30-day maximum flows in most catchments. Strong declines in monthly flows are most evident during summer, while notable increases were observed between January and March. The findings highlight the influence of climate change on streamflow seasonality in European montane regions, emphasizing the risk for protected wetland ecosystems within headwaters, as well as for water management downstream.