Nature of current and assessment of possible future changes in the water regime of lake Lebedyne (Sumy region)

Aim of the research is to identify the characteristic features of modern and predictive assessment until 2030 possible changes in the water regime of the Lake Lebedyne. Methods of the research - water balance method (to clarify the nature of modern changes in the water exchange of the lake), pairwise and multiple correlation methods (for statistical analysis of relationships between hydro-meteorological variables). Scientific novelty - for the first time the analysis of modern changes in the water exchange of the Lake Lebedyne by comparing the components of the lake's water balance for two periods - modern (1991-2019) with the period of the climatic norm (1961-1990); for the first time estimated for the next decade (2021-2030) changes in the water regime of Lake Lebedyne. Practical value is determined by the fact that the main provisions of this scientific research will be used when discussing a project to improve the state of Lake Lebedyne, which was provided for by the Program of Economic and Social Development of the city of Lebedin for 2020-2021 program years. Research results. It was revealed that the total volume of water inflow into the lake in the modern period (19912019) has decreased (compared to the period of the climatic norm - 1961-1990) by almost 16%. Of these, the inflow of water from the area adjacent to the lake (slope runoff) decreased by 17.8%, and the amount of atmospheric precipitation on the lake's surface by 11.7% also decreased. There is a decrease in the absolute volume of evaporation from the water surface of Lake Lebedyne due to a decrease in the volume of water inflow. However, at the same time, against the background of an increase in air temperature, the intensity of evaporation increases - its share in the water- balance ratios increased by 8.3% compared to the period of the climatic norm. Evaluating the accumulative component of the lake's water balance, it can be stated that during the period of climatic normal there was a certain accumulation of water in the lake - on average by + 22130 m3 annually. In the modern period, the volume of water in the lake was depleted - on average for the period 1991-2019 by - 81200 m3 per year. As a result, the volume of water in the lakebed in the modern period has decreased by about 40-42% compared to the period of the climatic norm. According to the forecast estimates of the values of the total water inflow into the lake Lebedyne for the period 2021-2030 it can be assumed that in comparison with the previous decade, they will grow by an average of 18%. Therefore, with a certain stabilization of the evaporation values, one can expect an insignificant, but nevertheless, replenishment of the lake with water.