Tendencies of changes in hydrometeorological parameters of the Caspian Sea in the modern period (1990s – 2017)

Abstract

Monthly mean values of hydrometeorological parameters from on-line databases (DAHITI — Database for Hydrological Time Series of Inland Waters, NASA Giovanni) and measurements at the top of the Volga River Delta have been used to study the interannual variability and assessment of trends in the level of the Caspian Sea and the Kara-Bogaz-Gol (KBG) Bay, Volga River runoff, atmospheric precipitation and air temperature over the sea, sea surface temperature (SST) of the Northern, Middle and Southern Caspian and KBG Bay in the modern period. The trends in hydrometeorological parameters turned out to be equal: the runoff of the Volga River in 1992–2016 to –2.5 km 3 /year; precipitation and air temperature in 2003–2017 to –0.21 mm/month/year and +0.04 °C/year, respectively; SST in the sea as a whole (without the KBG Bay) in 2003–2017 to +0.059 °C/year (in the Northern, Middle, and Southern Caspian and in the KBG Bay they were +0.050, +0.067, +0.087 and +0.106 °C/year, respectively). In the negative trends of both main components of the Caspian Sea water balance (Volga runoff and atmospheric precipitation), the level of the Caspian Sea decreased on the average. The rise of the level in 1993–1995 and its decline in 1995–1997 corresponded to changes in Volga runoff in 1992–1994 and 1994–1996. Later, the drop in sea level was determined mainly by evaporation from the sea surface which increased with the growth of air and water temperature under conditions of global warming. The average rate of decline in the sea level in 1993–2015 was approximately 5 cm/year; in the past 3.5 years (2015, 2016, 2017 and until mid-2018), the level remained practically unchanged at around –28 m.