The Caspian Sea, the largest inland body of water on Earth, is shrinking. Not fluctuating, not entering another natural cycle, but shrinking.
For decades, scientists and policymakers treated changes in the Caspian as part of the basin’s natural variability. Water levels in the sea have always risen and fallen.
But our new study shows something far more troubling: the current decline is increasingly driven by human decisions to dam and divert rivers, and by fragmented decision-making across five countries that border this body of water.
Using satellite observations together with ground-based hydrological records from rivers across all five shoreline states (Iran, Russia, Turkmenistan, Azerbaijan and Kazakhstan), we found that flow into the Caspian Sea has declined sharply over the past three decades.
The main reason is not declining rainfall. In fact, rain over the Volga Basin, which supplies roughly 80% of the Caspian’s inflow, has slightly increased. That finding matters because it overturns one of the most common assumptions surrounding the Caspian crisis. The common narrative has been straightforward: climate change increases evaporation, rainfall declines, and the sea shrinks.
Climate change certainly plays a role: our analysis confirms that evaporation across the Caspian has increased significantly as regional temperatures rise. But evaporation alone explains only about 40% of the observed water loss since the mid-1990s.
The remaining decline points overwhelmingly toward human activity. The Volga River has been heavily engineered for decades. Dams, reservoirs, use for irrigation, industrial consumption and navigation systems have fundamentally altered the hydrology of the basin).
Water that once flowed naturally into the Caspian is increasingly intercepted upstream. One critical but rarely discussed example is the Volga–Don canal system, which links the Caspian basin to the Black Sea through Russia’s internal waterways. Geopolitically and economically, the canal is strategically valuable. But it diverts water away from the Caspian system.
The cumulative effect is now visible from space. Since the mid-1990s, the Caspian Sea has lost roughly 24,000km² of surface area, an area approaching the size of Sicily. Water levels have fallen by about two metres.
The shallow northern Caspian, ecologically one of the most productive parts of the sea, is drying particularly rapidly. This matters because the northern Caspian is not empty water. It is a critical ecological zone supporting fisheries, wetlands, migratory birds and spawning grounds for sturgeon, the ancient fish species that produce most of the world’s caviar.
Read the full article on The Conversation
Suggested citation: Nima Shokri, Amir AghaKouchak. “The Caspian Sea has lost an area nearly the size of Sicily: human activities are a major reason why.” The Conversation, 22 June 2026. https://doi.org/10.64628/AB.cqakx5q7a
