Transformation of the Thermal Regime of the Kuibyshev Reservoir Against the Background of Global Climate Warming

Abstract

The purpose is to quantify the changes in the surface water temperature of the Kuibyshev reservoir and the shift in the dates of the transition of the water temperature during warming in spring and cooling in autumn through control values (0.2; 4.0; 10.0°C) in the context of global warming. Materials and methods. For the study, archival and modern data of synchronous observations of surface air temperature and surface water temperature of the Kuibyshev reservoir were used. Surface air temperature was measured at the meteorological station in Tolyatti on the border of the Middle and Lower Volga. The surface water temperature was measured at the stationary hydrological station of Togliatti in the coastal strip of the reservoir at a depth of at least 1 m according to a single method, from the moment the reservoir was created in 1957 to the present. Results and discussion. For a comparative analysis of the transformation of the thermal regime, two periods were selected: modern (2015-2021) and historical (1957-1980). It has been established that in the modern period there has been a change in the thermal regime of the Kuibyshev reservoir, there has been a steady upward trend in the temperature of the surface water layer in the coastal zone of the reservoir. In the modern period, the average water temperature for the ice-free period (April-November) increased by 1.6 °C compared to the historical period. In the seasonal range, the maximum increase in water temperature was 2.0 °C and was observed in July. In the modern period, the duration of the warm period has increased. The number of days between spring and autumn transitions of water temperature through the control values increased: by 14 days – for the value of 0.2 ºС; for 15 days – for a value of 4 ºС; for 8 days – for a value of 10 ºС. In the modern period, the reservoir warmed up faster and cooled more slowly. The spring transition of water temperature through 0.2, 4.0 and 10.0 ºС occurred earlier by 10, 2 and 5 days, respectively. And the reverse autumn transition through 10.0; 4.0 and 0.2 ºС was carried out later by 10, 10 and 6 days, respectively. Conclusions. An increase in air temperature over the water area of the Kuibyshev reservoir due to global climate warming caused an increase in water temperature and a shift in the control dates for the transition of water temperature through control values (0.2; 4.0; 10.0 °C).