Long-term trends in river flow: a case study of the Soła River (Polish Carpathians)

Cracow University of Technology, Department of Environmental Engineering, Institute of Engineering and Water Management, Warszawska 24, 31-151 Cracow, Poland

^⁎ Corresponding author: mariola.kedra@iigw.pk.edu.pl

Abstract

This study analyses potential trends in river flow for the most recent 60 years (1956– 2015). The study area is situated in the Soła catchment in the Polish Carpathians. The focus of the study was to evaluate long-term trends in mean monthly river flow for each season of the year as well as to compare the direction of these trends for sites located a distance upstream and downstream from a cascade of three dams built on the Soła River. Moreover, potential long-term trends in seasonal precipitation were also studied. The data indicate a significant increase in minimum discharge during the winter for the upstream site. Increases in mean and maximum discharge are significant for spring at that site as well. In contrast, a significant decrease in minimum discharge was identified for the downstream site during the spring. Moreover, significant decreases in mean and minimum discharge were noted for the summer season at the downstream site only. No trends in discharge were identified for the autumn at either site. Significant trends in precipitation were noted for each season of the year, with increases during the winter, spring, and autumn (3.6–9.8 mm per decade) in the vicinity of the upstream site, but a decrease in minimum summer precipitation (–5.0 mm per decade) at the downstream site. The revealed differences in the direction of seasonal trends for the upstream and downstream sites studied suggest an anthropogenic impact on river flow downstream from the cascade of dams. Overall, the identified decrease in summer discharge at the downstream site, accompanied by a decrease in summer precipitation, indicate the need for adaptive water management in the studied catchment to ensure water availability for the summer season.