Climate change and drought push Caspian Sea to lowest level on record

August 12 marks the International Day of the Caspian Sea, also known as the Day for the Protection of the Marine Environment of the Caspian Sea.

According to domestic media, this date has been observed annually since 2006, following the entry into force of the Framework Convention for the Protection of the Marine Environment of the Caspian Sea.

The Framework Convention was developed by experts from the Caspian littoral states with the support of the UN Environment Programme and other international organisations. Negotiations on the text took place between 1995 and 2003 at various meetings and culminated in the signing of the document by the Caspian states on November 4, 2003.

This agreement, known as the “Tehran Convention” after the city where it was adopted, aims to prevent pollution of the Caspian marine environment from all sources and to protect, conserve, and restore its ecological balance. It also contains provisions for the rational and sustainable use of the Caspian’s biological resources, environmental impact assessments, ecological monitoring, and scientific research. After ratification by the governments of the five littoral states, the Tehran Convention entered into force on August 12, 2006, and the date has since been celebrated as Caspian Sea Day.

The Framework Convention for the Protection of the Marine Environment of the Caspian Sea is the first legal agreement among the five coastal states reflecting the environmental protection needs of the region and establishing the corresponding organisational mechanism.

On August 12, 2018, during the Fifth Summit of the Heads of the Caspian States in Aktau, Kazakhstan, the Convention on the Legal Status of the Caspian Sea was signed. Over the past 30 years, climate change has been particularly evident in the Caspian basin. As a result, populations living along the coast have increasingly faced the negative impacts of major climate fluctuations, changes in sea levels, floods, and droughts.

The decline in the Caspian Sea’s level due to climate change has become a potential threat to the region. The reduced inflow of rivers into the sea is explained not only by decreased precipitation but also by increased water withdrawals for agricultural needs.

Instrumental measurements of the Caspian Sea’s level have been conducted since 1840. During this period, the highest level was recorded in 1882 (−25.2 meters according to the Baltic System), and the lowest in 1977 (−29.0 meters), with a fluctuation amplitude of 3.8 meters.

In the 20th century, three prolonged periods of relatively small fluctuations can be identified. In the first period (1900–1929), the level remained almost stable at around −26.3 meters. In the second period (1930–1977), the level steadily declined — falling by 1.75 meters between 1930 and 1938 — and in 1977 reached −29.0 meters for the first time, with the sea’s area shrinking by 48,000 square kilometres. In the third period (1978–1995), the level rose sharply by 2.0 meters.

From the late 20th century into the first decades of the 21st, the level began to decline again. In 2020–2023, the Azerbaijani sector of the Caspian saw a 75-centimetre drop, and by January 1, 2024, the sea level stood at −28.7 meters (Baltic System).

The numerous factors affecting sea-level changes over different periods can be grouped into four main categories: cosmogeophysical forces, geological and geodynamic processes, hydrometeorological processes, and anthropogenic factors.

Analysis of cause-and-effect relationships shows that long-term fluctuations in the Caspian Sea level are an integrated indicator of large-scale moisture circulation in the ocean (North Atlantic)–atmosphere–land (Volga River basin) system. In the 20th century, inflow from the Volga basin accounted for about 64% of level fluctuations. When taking into account inflows from around 130 other rivers, including the Kura, Ural, Terek, and Sulak, this figure rises to 70%.

The remaining 30% is mostly due to evaporation. Between 1980 and 2020, the average annual air temperature in the Caspian region (sea and surrounding territories) rose steadily by 0.030°C per year, increasing overall by 1.2°C — a factor that accelerated evaporation.

In November last year, Azerbaijan hosted a major international event — the 29th session of the Conference of the Parties to the UN Framework Convention on Climate Change (COP29). As part of COP29, events were held focusing on the Caspian Sea’s problems. In addition, ministers and senior officials of the Caspian littoral states adopted a Declaration on strengthening cooperation in connection with the declining Caspian Sea level.

By Tamilla Hasanova