Impact of Anthropogenic Activity in the Upper Danube Basin on the Danube Water Temperature Regime at Bratislava

Abstract

The man activity in the basin affects the water temperature in the increasingly higher levels (construction of water reservoirs, construction of thermal and nuclear power plants or drainage of waste water to streams). In this paper, we focused our attention on the evaluation of the impact of anthropogenic activity to increase the thermal load of the Danube River for the period 1926–2020 at the Bratislava (Slovakia) station. In the first part, the long-term trends of a series of monthly and annual water temperatures in the Danube (period 1931–2020) are identified. In the second part, the dependence of the range of daily water temperature values is analysed at the temperature of the atmosphere in Vienna. The impact of an increase in the temperature of the Danube water due to human activity was tried to identify for lower, average, and higher flows (for Danube discharge at Bratislava water gauge 1500 m3s-1, 2000 m3s-1, and 3000 m3s-1) by comparing two periods: 1932–1961, and 1991–2020. As the effect of water heating in the river stream is most noticeable during low flow (dry) periods and high air temperatures, only daily water and air temperature data from the warm months between May and September were used in the calculations. At monthly flow rates of 1500 m3s-1, the water temperature was, on average, 0.5°C higher during the period of 1991–2020 than it was during the period of 1932–1960. This growth could be attributed to human activities in the Danube basin above Bratislava (warming of water in the built tanks, the wastewater flow to the Danube flow, etc.)