The influence of reservoirs on water temperature in the downstream of Ipeľ

The temperature regime of river systems is influenced by seasonal temperature stratification in reservoirs and climate change.The release of cold water from reservoirs can affect river temperature, with a decrease in river temperature during warm periods and an increase in river temperature during winter.However, warmer air temperatures and increased solar radiation may reduce the influence of reservoirs on downstream temperatures in the future.The cooling potential of reservoirs remains strong for river reaches downstream of reservoirs with strong temperature stratification.The study analyzed air temperature trends at two climate stations, Boľkovce and Málinec, over different time periods.Data on the temperature of the water were collected from a number of stations located above the reservoirs: Smolná I and Smolná II and Málinec, and several stations below the reservoir, namely Málinec, Kalinovo, Holiša and Slovenské Ďarmoty downstream of the Ipeľ River.The Málinec Reservoir, which regulates the upper part of the Ipeľ River and serves as a drinking water reservoir, was built in 1986-1993 and put into operation in 1994.The analysis was divided into two parts.The first part analyzed data from stations with time series before the construction of Málinec reservoir, while the second part analyzed data from stations with time series after the construction of the reservoir.Increasing water temperatures were observed throughout the year, while increasing air temperatures were significant in warm months.The influence of the reservoir can be seen in the slight change of the mean monthly temperatures.The mean temperature decreases in the summer months and increases in the winter months in the period after the construction of the reservoir.