Hydrometeorological Parameters of the Marine Environment in the Russian Sector of the Caspian Sea under Changing Climate

Abstract

The paper summarizes the data from long-term observations of hydrometeorological parameters in the Caspian macro-region. The average annual air temperature over the past 30 years at stations in the Russian part of the Caspian Sea has increased by 1.0°C and the temperature of the surface water layer by 0.3°C. Currently, the total river runoff into the sea is about 275 km3. The volume of annual runoff from all rivers flowing into the Caspian Sea went down in the 1996–2020 period compared to the 1961–1990 period. The intensity of the decrease in river runoff in the 1996–2020 period averaged 0.12 km3 per year, while the flow of the Volga and Kura rivers decreased most intensively. In conditions of warming and decreasing river runoff, the Caspian Sea level continues to decline, which began in the late 1990s. Due to increasing water scarcity in the Volga River, the level of the Caspian Sea is going down. The trend started in the late 1990s. By the beginning of 2023, the average sea level had reached –28.70 m abs, which is about 2 m lower compared to the level in 1995. The drained coastal territories are assessed at more than 22 thous. km2, mainly in the northern shallowest part of the sea. The changes in the wind regime and the observed increase in the average monthly and yearly wind speeds are compared against those in the standard reference period (1961–1990). It has been established that the easterly and westerly winds, which cause storm surges with devastating impact on coastal territories, have the greatest repeatability. The statistics of surges observed at four marine stations are given for the 2010–2021 period. The amplitude of the wind-induced level fluctuations in the Lagan area reaches a maximum value of 3.0–3.5 m, while it is about 1 m in Makhachkala. An analysis of the seasonal variability of surges is also given.