The Kuibyshev Reservoir water level increasing in the context of the climate change

Assessing the change in the hydrological regime of the reservoirs of the Volga-Kama cascade is very relevant in the context of global warming. Reservoirs are used for domestic and drinking water supply, fisheries and recreation. The largest in the cascade, the Kuibyshev Reservoir, was chosen as the object of study. It is characterized by a seasonal regime of regulation of the Volga water flow. The main objective is to quantify interannual and seasonal changes in the reservoir water level for the period from 1958 to 2024. Relevance. Methods. The institute has created a database of instrumental observations of the reservoir water level and water flow in the Zhigulevsky hydroelectric complex. 97% of the Volga River’s water flow passes through the hydroelectric complex. The source material was processed using the method of statistical analysis of time series. We conducted regression and correlation analyses. The reliability of the estimates was determined using Fisher’s criterion. Results. The stable trend of increasing the average water level of the Kuibyshev Reservoir was formed due to the increase in the water level during the winter low water period and spring flood. The average annual water level increased by 0.93 m over the 67-year period. The rate of increase was 0.14 m/10 years, in accordance with a linear trend. A connection has been established between the water level in the reservoir and the water flow of the Volga River. The correlation coefficient is 0.55. Changes in water levels across hydrological seasons occurred extremely unevenly. The water level increased most significantly during the winter low water period by 1.88 m at a rate of 0.28 m/10 years. The water level rose by 1.30 m during the spring flood. The rate of increase was 0.20 m/10 years. The water level remained virtually unchanged during the summer-autumn low water period. The main factor in the increase in water levels is the change in the seasonal regulation of the Volga River water flow at the Zhiguli hydroelectric complex. As a result, the amplitude of seasonal fluctuations in water levels decreased by half, from 4.6 m to 2.3 m, due to a significant increase in water levels during the winter low water period and spring flood. Such significant changes in the water level during the winter low water period (December-February) and the beginning of the spring flood (March, April) led to changes in the morphometric characteristics of the Kuibyshev Reservoir. The largest increase in the area and volume of the reservoir occurred in the month of March and amounted to 26 % and 32 %, respectively.