Scientists have calculated the decrease in the area of the Caspian Sea over the past 30 years

A team of Russian researchers has studied the reduction in the area of the Caspian Sea and the Kara Bogaz Gol Bay from 1993 to 2025. According to the Russian Science Foundation (RSF), the results of the work supported by a grant from the organization have been published in the journal Modern Problems of Remote Sensing of the Earth from Space.

The level of the Caspian Sea has been continuously decreasing since 1995 at a rate of about 10 cm per year. During this period, the indicator fell by almost 3 m. Scientists have developed a technique based on the analysis of high-resolution satellite data, which allowed us to obtain modern hypsometric curves that will help assess the actual loss of water mirror area. These data are necessary for accurate calculation of the water balance and evaporation from the surface of the reservoir.

"We needed to obtain modern hypsometric curves for the Caspian Sea and the Kara Bogaz Gol Bay separately based on data from the Landsat-5, -7 and -8 satellite sensors with a spatial resolution of 30 m for 1993-2025. In addition, we wanted to find out how much the area of the Caspian Sea has actually decreased and where the shallowing of the Caspian Sea is taking place on the largest scale," said Andrey Kostyanoy, head of the Russian Science Foundation grant, Chief Researcher at the P. P. Shirshov Institute of Oceanology of the Russian Academy of Sciences.

The shallowing has already led to negative consequences for the region. In particular, navigation is hampered by falling water levels in the Volga-Caspian Sea Canal and ports, and the coastline has begun to move away from populated areas. According to experts, by the end of the 21st century, sea level may decrease by another amount from 2 to 21 m. The new methodology will allow us to quickly assess the further reduction in the area of the sea and bay.

The experts analyzed the data for the period from 1993 to 2025. It has been established that in 2025 the level of the Caspian Sea dropped to -29.4 m. This figure was lower than the historical low of 1977, when the sea level was -29.0 m. Scientists found that the area of the Caspian Sea mirror decreased by 28,644 square kilometers from 1996 to 2025, which is 7.4% of the figures from 30 years ago. According to experts, over the past decades, the Caspian Sea area has lost a territory comparable in size to the area of Albania.

In the course of the work, the researchers obtained regression equations with a high statistical relationship (correlation coefficients 0.95–0.99). Scientists recommend using them to calculate the area of the Caspian Sea at levels from -26 to -29 m, as well as to assess the state of the Kara Bogaz Gol Bay at levels from -27.1 to -31 m.

"The results obtained are important for assessing the so-called morphometric factor and its role in the water balance of the Caspian Sea, namely in reducing evaporation from the decreasing mirror of the Caspian Sea with a decrease in its level. This factor should slow down the rate of sea level decline, all other things being equal," Kostyanoy commented on the results of the work.

However, satellite altimetry data has not yet confirmed a slowdown in the process. If in 2005-2019 the sea lost an average of 8.16 cm of sea level annually, then in 2020-2024 this rate increased to 22.7 cm per year. According to Kostyanoy, the interannual variability of the components of the water balance of the Caspian Sea still significantly exceeds the effect of reducing the evaporation area.

The study involved employees of the P. P. Shirshov Institute of Oceanology of the Russian Academy of Sciences, the Geophysical Center of the Russian Academy of Sciences, Tver State University and NPO Impulse JSC.

Bottom line: what will the shallowing of the Caspian Sea lead to?

Coastal countries are talking about the disaster and sounding the alarm

On May 11, Russian scientists recorded a rapid increase in the coastline of the Caspian Sea against the background of ongoing shallowing. According to experts, changes in the coastline occur on both existing and newly formed islands.

Mikhail Bolgov, an employee of the Institute of Water Problems of the Russian Academy of Sciences, said on April 4 that the Caspian Sea will not disappear in the foreseeable future, and its level has reached an equilibrium state after 20 years of decline. According to him, the sea level may fluctuate around the equilibrium state with a large forecast interval.