Abstract
This study analyses potential trends in river flow for the most recent 60 years (1956– 2015). The study area is situated in the Sola 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 Sola 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.
Highlights
In mountain regions of mid-latitudes, stream and rivers are typically rich in water owing to substantial orographic precipitation
For winter (December–February, Fig. 2) and spring (March– May, Fig. 3), increasing trends were noted for the upstream site (Żywiec) only; an increase in minimum Q (0.67 m3s–1 per decade, strong evidence) during the winter was followed by an increase in mean and maximum Q during the spring (1.35 and 2.03 m3s–1 per decade, respectively, Figs. 3a–b)
In the conducted analysis pertaining to changing flow conditions in a mountain river, long-term (60-year) trends in river flow for each season of the year (1956– 2015) except autumn were found
Summary
In mountain regions of mid-latitudes, stream and rivers are typically rich in water owing to substantial orographic precipitation. Mountain rivers are affected by human activity, which directly (water diversion, dam and reservoir construction, channel engineering works) or indirectly (urbanization, removal of vegetation, road construction) [2,3], alters flow and thermal conditions, impairing river ecosystems [4]. Of direct interventions in river environments, the construction of dams and the changes to fluvial environments that they introduce, have been well documented [5,6,7,8,9,10,11,12,13,14,15,16]. Dams with hypolimnetic (bottom layer) water releases can weaken the synchronous behaviour of air and water temperatures and significantly change water temperature dynamics in the downstream river section [18,19]
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