Effects of the Time Period Length on the Determination of Long-Term Mean Annual Discharge

Currently, the 40-year-long reference period 1961–2000 is used in Slovakia for systematic assessment of hydrological regime. The World Meteorological Organization recommends unifying climatic normal 1991–2020 with a characteristics purpose climate change research. We have analyzed changes long-term mean annual discharges at 113 water-gauging stations over different time periods. Considering history periods Slovakia, we focused on analysis 10, 20, 30, 40, and 50-year-long moving averages 1961–2020 comparison whole selected period. deviations flow rates area river sub-basins been analyzed. results indicate that new to be should include after year 2000. To determine its precise length, more detailed needed.