Changing trends of river flows in the Upper Vistula Basin (East-Central Europe)

Abstract

The mean annual, winter half-year and summer half-year flows at 86 water level gauges in the Upper Vistula Basin in the years 1951–2015 were examined. The Ward’s hierarchical cluster analysis was used for grouping sub-catchments in reference to the standardized aforementioned flows. Trends analysis was performed for each cluster of catchments in all combinations of periods not shorter than 20 years. Spatial distribution of clusters of catchments has been analysed according to geographical locations. There are observed different trends in distinguished groups of catchments, wherein the substantial differences concern long-term trends. Changes in trend direction in the years 1951–2015 were revealed, which indicate flow fluctuations. Presumably, physiographical heterogeneity of the Upper Vistula Basin is reflected in no unequivocal trends occurring in clusters of catchments. Some similarities were stated in short-term trends occurring in particular groups of catchments.