Wieloletnia zmienność wiosennego odpływu rzek polskich

The time series of daily runoff observed in 16 water-gauging stations in Poland in the period 1966-2006 have been subject to analysis of change. In order to detect changes in streamflow in spring of each year, the 95% percentile time series for streamflow from February until April was analysed. Moreover, the day on which 50% of the mass of the total annual streamflow occurred (CMD, the center of mass data) was determined. Three statistical tests were used for the analysis of the time series: linear regression, Mann-Kendall test and Spearman's rank correlation. Interpretation of the results is presented, with statistical significance of changes. It has been found that for most of the stations analysed, trends in 95% percentile indicate a decrease.The analysis of the CMD time series did not detect the existence of a significant long-term trend since only small changes have been found. The spring runoff occurred earlier in some catchment (negative trends), although in the catchments selected it occurred later (positive trends).