Caspian Decline Threatens Biodiversity, Human Infrastructure

Date: 11 April 2025 - 22:56

News ID: ۱۳۸۳۵۵

LONDON (University of Leeds) --
Water levels in the Caspian Sea—the world’s largest landlocked water body—are getting lower, as hotter temperatures cause more water to evaporate than is flowing in. Even if global warming is limited to below 2°C, it is likely that the level of the Caspian Sea will decline by 5 to 10 m, but if temperatures rise further, water levels could drop by as much as 21 m by 2100.
Researchers led by Leeds have mapped the potential risks this poses to the region’s biodiversity and human infrastructure, in a paper published in Communications Earth & Environment.
The findings show that an area of 112,000 km2—which is larger than the size of Iceland—is likely to dry up, even in an optimistic scenario for global warming with a 10 m decline. Since many of the most ecologically and economically important areas are located in shallow water, this could have significant consequences for biodiversity and the sustainability of the region’s human population.
The Caspian Sea is home to the endangered Caspian seal and six species of sturgeon, as well as hundreds of species of fish and invertebrates found nowhere else. According to the research, the declining water levels will leave Caspian seals with significantly reduced breeding habitat, restrict access to spawning rivers for sturgeons, and lead to the loss of coastal lagoons and reed beds important for the spawning of other fish species and migrating birds.
More than 15 million people live around the Caspian coast, in Azerbaijan, Iran, Kazakhstan, Russia and Turkmenistan. The bordering nations rely on the water body for fishing, shipping and trade, and the sea is important for regulating the climate in Central Asia.
In the northern Caspian, the findings show that some settlements, ports and industrial facilities could end up being stranded tens or even hundreds of kilometers from new shorelines. The exposed dry seabed is likely to release dust containing industrial contaminants and salt, posing serious threats to human health, as previously occurred with the drying of the Aral Sea.
The researchers say policymakers and conservationists need to take a dynamic approach to biodiversity protection, rather than relying on traditional protected areas with fixed boundaries, since these may quickly become obsolete due to the rapidly changing water levels.
Dr. Simon Goodman from the School of Biology at the University of Leeds, who supervised the research, said, “Some Caspian Sea level decline appears unavoidable, even with action to reduce global greenhouse gas emissions. However, with the anticipated effects unfolding over a few decades, it should be possible to find ways to protect biodiversity while safeguarding human interests and well-being.
“That might sound like a long timescale, but, given the immense political, legislative and logistical challenges involved, it is advisable to start action as soon as possible to give the best chance of success.”
Currently the Caspian Sea extends approximately 1,150 km by 450 km, with a total area of 387,000 km2.
With a 10 m decline, four out of 10 ecosystem types unique to the Caspian Sea would be expected to disappear completely, and the coverage of existing marine protected zones (areas earmarked for conservation) would be reduced by up to 94%.
Caspian seals give birth to their white-coated pups between mid-January and early March on ice in the northern Caspian Sea. However, the research shows a 5 m decline could reduce the area of this habitat by up to 81%—putting huge stressors on their already reduced population.
The Caspian seal was listed as Endangered by the International Union for the Conservation of Nature (IUCN) in 2008, and is included in the national Red Books of all five Caspian countries, signifying its recognition as a species at risk of extinction.
The decline will also make all current and historical haul-out sites—areas on land where seals rest—inaccessible. While receding water levels may create some new islands, further research is needed to assess their suitability for seals.
Sturgeons are an ancient family of large fish, and critically endangered due to overfishing for their meat and caviar (fish eggs or roe). The fish usually inhabit shallower parts of the sea in summer and autumn, but these areas are facing a potential reduction of 25% to 45% due to the fall in water levels, which may stop them accessing their few remaining spawning sites in rivers that flow into the sea.
The Caspian Sea is also a globally important habitat for birds migrating between Europe, Asia and Africa. Migratory birds rely on coastal lagoons and reed beds for resting, shelter and food during their migrations, but such habitats are vulnerable to loss as waters recede.
Biodiversity in the Caspian Sea is already threatened by over-fishing, introduction of invasive species and pollution. Although work has been done to protect areas important for biodiversity, the paper predicts that overall coverage of existing Caspian marine protected areas disappear almost entirely for all countries except Kazakhstan, which would retain about 5% of current coverage.
Rebecca Court, Ph.D. researcher in the School of Earth and Environment at Leeds, worked on the research as part of her Masters degree in the School of Biology. She said, “We hope this research will help to raise awareness of the trajectory and potential impacts of the falling sea level. The mapping should better equip policymakers and conservationists to plan for and address the numerous issues in advance.”
The findings also predict a concerning trajectory for industry, with critical ports in all bordering countries being impacted. Baku (Azerbaijan), Anzali (Iran), and Aktau (Kazakhstan) are expected to experience increases in distance to shore of 1 km or more, while Turkmenbashi (Turkmenistan), and Lagan (Russia; planned future site), could see increases of 16 km and 115 km respectively, according to the paper.
The Volga is the only river connecting the Caspian to the outside maritime world, and this vital trade route could be critically compromised by declines of just 5 m.
The Kashagan (Kazakhstan) and Filanovsky (Russia) oil fields in the northern Caspian are two of the region’s most important hydrocarbon production sites. Production currently occurs at offshore installations, with ship-based logistics, but these will become landlocked if Caspian Sea levels decline by 5 to 15 m.
Coastal communities in the north are likely to be hit hard as income from fishing disappears, and harsh climatic conditions make other economic activity like agriculture more difficult, potentially threatening social stability.
Some cities around the Caspian use desalination (removing salt and minerals from saltwater) for fresh water supplies, and water level declines are already impacting desalination operations at Aktau in Kazakhstan.
Loss of water from the Caspian could also affect the regional climate, leading to reduced rainfall and drier conditions across central Asia with indirect impacts on agriculture.
The energy resources of the Caspian Sea make it important geopolitically, so social, economic and environmental instability due to climate change could have worldwide repercussions.
Going forward, a balance needs to be struck between protecting biodiversity and human prosperity and well-being. The researchers’ recommendations include:
Investing to enhance regional capacity for biodiversity monitoring, conservation planning and sustainable development
Supporting coastal communities to diversify economically and develop resilient infrastructure
Developing legislation that enables the creation of protected areas with flexible borders
Taking a pre-emptive planning approach to avoid conflicts between biodiversity protection and efforts to adapt human infrastructure
Tracking rapidly changing ecosystems and implementing species translocations and ecosystem restoration where needed
Reducing greenhouse gas emissions at a global scale.
The researchers stress that urgent action is needed, with coordinated regional planning and global collaboration, to mitigate the projected impacts.
Dr. Elchin Mamedov from the Ministry of Ecology and Natural Resources, Azerbaijan, said, “This is an important study because it highlights the risks posed by climate change for Caspian region biodiversity and local communities and the need to enhance regional and international cooperation to help manage the impacts.”