Mekong dams must release less water in dry season to preserve habitats, experts say

Abnormally high-water levels in the Mekong River at the end of May indicate that dams on the river must release less water during the dry season to protect the ecosystem, experts said at an online panel Monday. 

Rain levels during the dry season this year have increased, experts told an online seminar about the unseasonably wet 2022 dry season, hosted by the Washington-based Stimson Center. But they singled out dams, particularly in China and Laos, as adding to the problem of flooding along the lower half of the river, threatening the ecosystems there.

The Mekong region is home to numerous species of plants and animals that rely on its annual changes from dry season to wet season and back again, the panelists said. Disruption of the cycle is harmful to many of the species, and in turn the riparian communities that depend on them.

“I think our data shows that very clearly the river level there is much higher during the dry season than normal … and China’s dams actually can be part of the solution,” Brian Eyler, Southeast Asia program director of the Stimson Center and co-lead of its Mekong Dam Monitor Project, told the panel on Monday.

“They wield a lot of power over the downstream, particularly those two largest dams,” he said. “We found that they can they alone can raise the river level by 50 percent … for total dry season flow. That’s power,” he said, adding that the dams could also help to restore natural flow in times of need.

The Mekong River Commission, an intergovernmental body that helps to coordinate management of the river, reported that May 2022 was the second wettest May since it began collecting data. Total flow in May was 22.8 billion cubic meters, about 150% higher than the average flow of 9 billion cubic meters.

The Mekong Dam Monitor’s data suggested that about 6 billion cubic meters from the flow came from dam releases upstream, mostly in China.

An example of how the increased flow could affect species is the Mekong Flooded Forest, said Ian Baird, a geography professor at the University of Wisconsin-Madison.

The World Wildlife Fund said the flooded forest is “a spectacular 27,000 km² complex of freshwater ecosystems including wetlands, sandy and rocky riverine habitats in northern-central Cambodia, bordering the South of Laos.”

Baird said that the forest’s most striking feature, trees that jut upward from the floodwaters, relies on drier periods when the trees are not submerged.

“Right now what we can see is that, the bushes that are in the lowest part of the river have been heavily impacted. The Blodgett trees have [exhibited] medium impacts,” he said.

“So, I mean, things are already bad, but it’s important to understand that they could get a lot worse than they are now. And really the way to mitigate this is to release less water in the dry season,” Baird said.

But he said that decisions about upstream releases are mostly beyond Cambodia’s control.

“This is all water coming from above Cambodia, you know, but there is a lot that China and Laos could do, especially China, I think, that that could reduce the impact.”

The Mekong River ecosystem could be lost if nothing is done, Chea Seila, project manager of the Wonders of the Mekong, a research group that receives funding from the U.S. Agency for International Development.

She brought up the world record 300-kilogram giant freshwater stingray that was recently caught, tagged by her team and released in Stung Treng.

“The discovery of this [world record breaking] fish indicates the special opportunity that we have in Cambodia and also to protect the species, and also the core habitat,” she said.

Eyler of the Stimson Center said that although existing dams could help keep the river’s flow closer to expected averages, building more could create new problems.

“I would not recommend building more dams to counter this effect, which is a discourse that we’re hearing coming out of the Mekong River Commission, that there’s an investment solution to this, there’s an infrastructure solution to this,” he said.

“I think that’s a very expensive, dangerous and risky proposition, particularly when there are solutions at hand,” Eyler said.