Climate change is the dominant force behind the falling water level of the Caspian Sea and outweighs human intervention such as upstream damming, water policy researcher Anoush Nouri Esfandiari said on July 22.

The world's largest enclosed body of water, surrounded by Azerbaijan, Iran, Turkmenistan, Kazakhstan and Russia, has been losing surface level for years in a sustained decline that can no longer be attributed to natural fluctuation alone, a trend that carries consequences for the shipping, fisheries and coastal tourism economies of the five littoral states, including Iran's northern provinces.

Esfandiari, secretary of the Iranian Water Policy Research Institute, does not deny that abstraction from Russian rivers feeding the Caspian affects the decline, but holds that the role of climate change is greater than human intervention.

"Water abstraction from the rivers flowing into the Caspian Sea certainly affects the falling water level and shrinkage of this sea, but as far as I know, the Volga river, which supplies more than 80% of the Caspian's inflow, mostly has dams that function for navigation, and abstraction from it is limited," Esfandiari said.

"For this reason, in my view climate change is still the more decisive factor in the shrinking and falling level of the Caspian Sea, and its role is more prominent compared with other factors," he said.

On measures Iran has taken to prevent the sea shrinking, Esfandiari said the country had built numerous dams on the rivers feeding the Caspian, in particular the Sefidroud and its tributaries, and had brought a large part of the flow under control. "But the share of these rivers compared with the Volga is not very large, so the effect of these measures at the scale of the whole Caspian Sea will be limited," he said.

More than 80% of the inflow comes from the Volga River, which is extensively dammed and regulated along its course in Russia. These structures, numbering in the dozens, hold back substantial volumes of water for hydropower, irrigation, and industrial use before the river reaches its delta in the Astrakhan region. Additional outflows through the Volga-Don Canal further reduce water available to the sea's basin.

Water-intensive agriculture and industry in Russia, Azerbaijan a has been further exacerbating the problem. Since 2022, Russia has expanded irrigation along the Volga basin in an effort to boost domestic grain production. The increased use of the Volga river for agricultural needs was driven by Russia's invasion of Ukraine and the resulting sanctions on Moscow, which led to trade disruptions and food import restrictions.

Zaur Shiriyev, a nonresident scholar at the Carnegie Russia Eurasia Center, noted in an article published by Carnegie Endownment that these changes have intensified demand for water upstream, limiting outflow to the sea.

"One of the important problems we face today is the pollution of the Caspian's coastal waters," he said. On efforts to reduce coastal pollution, he said schemes to collect and dispose of sewage were being implemented, but that the projects had dragged on for years and had not yet reached full operation. "With the rising population in the northern provinces, in particular Mazandaran, pollution of coastal waters has become one of the serious challenges of this region," he said.

On the state of Tehran's groundwater despite last year's rainfall and rain earlier this year, Esfandiari said no marked change had occurred. "There may have been a slight easing of pressure on the aquifers from this year's rainfall, but groundwater resources are not restored over a short period, and rapid improvement cannot be expected," he said.

Asked whether incentive and penalty policies for subscribers could help manage water consumption, he said: "Not really, because in many residential complexes water consumption is calculated on an aggregate basis, and these policies have no direct effect on the behaviour of individual subscribers."

On the main drivers of high water use in the case of Tehran which hosts 10mn residents, Esfandiari said consumption was not limited to the domestic sector, with industry, green spaces and losses in the distribution network accounting for a significant share. He said treated wastewater had been intended to irrigate green spaces and much of the infrastructure had been built, but that the plan had stalled because of a lack of coordination between the municipality and the water company.

"As far as I know, the use of treated wastewater to irrigate green spaces remains unresolved," he said. "It was expected that the city council would play a more active role and, as a mediator, create the basis for agreement between the responsible bodies." He said resolving the treated-wastewater issue could serve as a suitable model for other large cities.

On drought across Iran's central plateau this year, Esfandiari said conditions were not uniform. "Conditions across the entire central plateau are not the same. The southern parts have had better rainfall than average this year, but in many areas no marked change has occurred," he said. "A single assessment cannot be given for the whole central plateau, because in some areas conditions have been better and in others no significant change has been observed."