THE IMPACT OF CLIMATE CHANGE ON THE WATER REGIME OF THE RIVER STYR IN VOLYN REGION

Abstract

The article analyses the impact of climate change on the water regime of the Styr River in Volyn region. Under the conditions of further climate change, the conditions of natural moisture supply will deteriorate, which will negatively affect the hydrological regime of water bodies. Compared to the last century, there has been a significant increase in the volume of annual river runoff, and water levels in Ukrainian rivers have been below normal for several years. Rising temperatures and changes in the moisture regime, if projected negatively, could lead to further transformation of river flows, deterioration of water quality and, consequently, problems with water supply and availability in certain regions. The annual average air temperature in 2022–2023 was 9.4 and 10.4 °C, respectively, which is 0.9 and 1.9 °C above the norm (8.5 °C). The year 2023 was the first in the ranking of the warmest years on record in Lutsk. No negative temperatures were recorded in winter. There was an upward trend in average monthly temperatures, which is in line with global trends. The water temperature was higher than the air temperature in all months. However, as winter temperatures rise, both the period with ice phenomena and the duration of the ice-freeze-up are shrinking. Recently, the probability of ice-free conditions has increased significantly. The annual precipitation was higher in 2022, amounting to 736 mm, and 680 mm in 2023. The increase in winter air temperature contributes to changes in precipitation patterns, with a greater proportion of mixed and liquid precipitation, more frequent thaws, and therefore insufficient snow accumulation to form high water floods. This trend of lack of stable snow cover has been observed in recent years. The highest water levels were recorded in 2023, when the average water level was 348 cm, and in 2022 – 316 cm. Maximum levels were observed in spring and minimum levels in summer and autumn. During the observed period, there was a tendency to decrease the average monthly and annual water consumption from 24.8 to 29.8 m3/c (2022–2023) compared to 2006–2013, when the average annual water consumption ranged from 40.1 to 51.2 m3/c. A close correlation between water flows and water levels has been established. In addition, there is a medium to strong correlation between water and air temperature and water discharge; a weak correlation between precipitation and water discharge and water levels. The increase in winter temperatures has caucused changes in the river’s water regime, including the absence of snow cover, the extension of the floods over time, which leads to a decrease in water flow, and the absence of ice cover. The analysis of the water regime makes it possible to use water rationally in economic activities and to carry out balanced water management in the Styr River basin.