Current Hydrological Regime of the Volga Reservoirs

The study is focused on variations of air temperature in the basin of the Volga reservoirs, the total inflow into the water bodies, their water exchange, water level and temperature, and the heat content of water mass in open-water period under various climate conditions. The object of the analysis is the long-term series of hydrometeorological data processed by statistical methods. It is shown that the present-day air temperature has increased by 1.3‒1.8°C compared with the period before 1976. The rate of warming was on the average 0.50°C/10 years. The volume of annual inflow increased by 12.4%. Three low-water and 4 high-water phases were identified in the reservoirs of the Upper Volga, including 29–31 low-water, 25–31 high-water, and 8–16 medium-water years. During the low-water phases, the volume of inflow into the reservoirs is 10–28% less than the long-term average, while in high-water years, it is 4–20% higher. The coefficient of water exchange in the reservoirs decreased or increased by 5–13% relative to the values obtained earlier. An increase in the winter and a decrease in the spring inflow were recorded in the reservoirs of the Upper Volga and in the Kuibyshev Reservoir. A tendency toward an increase in the normal annual water level was observed in the reservoirs in the upper part of the Volga and in the Kuibyshev Reservoir, while in the lower Volga, the normal annual level somewhat decreased. In low-water phases, the reservoir levels were on the average 17 cm below and in the high-water phases, 10 cm above the normal annual value. An increase in air temperature during the warm season in the reservoir water areas, on the average by 1.2°C, led to a synchronous increase in the temperature of the water mass by 1.1°C. At the same time, the heat content of the water mass of the reservoirs increased, on the average, by 24% in the upper part of the Volga and by as little as 2–11% in its lower part