China last week agreed to share year-round data from the upper Mekong River with downstream countries, where its dams are being blamed for muting the natural rhythms of one of Asia's great waterways and adding to the pain of recent droughts.
For the past 18 years, China has been sharing rainfall and water level data from two dam sites in the upper Mekong basin, where the river begins, during the bulk of the region's wet season, from June to October.
On Thursday it formally agreed to share the same data from the two sites all year with the Mekong River Commission, an inter-governmental body of the lower Mekong countries charged with managing the waterway. Cambodia, Laos, Thailand and Vietnam, which comprise the commission, have been urging Beijing to share the data for years.
A 'landmark' deal
In a prepared statement the commission secretariat CEO, An Pich Hatda, called the agreement a "landmark" in relations with China that would help downstream countries forecast coming floods and droughts.
Some 60 million people south of China live off the water, fish and soil the Mekong washes their way.
Experts say the year-round data should help give farming and fishing communities along the Mekong advance warning of sudden drops and rises that can break down riverbanks, kill off riverside crops and strand or wash away fishing boats.
"In northern Thailand and Laos in particular, but also in other parts of the lower Mekong basin, it should help somewhat because you do need more data to more accurately predict and forecast river levels and flows," said Gary Lee, Southeast Asia program director for International Rivers, a research group that advocates for sustainable river management.
But he said that forecasting loses steam the further down the river those communities are and that even the data China has been sharing up to now can come later than it should, sometimes with only a few days notice.
Marc Goichot, Asia Pacific water lead for the World Wide Fund for Nature, agreed that the new data will help with forecasting. But he said its greater gift may be what light it can shed on why the Mekong's seasonal variations are falling out of step with the river's historic rhythms.
He said speculation on the root causes has focused on three ideas: climate change, which may be disrupting rain cycles; evolving land use, which may be driving rain into the river more suddenly by allowing less of it to seep into the soil; and finally hydro power dams.
To date, China has built 11 dams across the upper Mekong, some with giant reservoirs holding back mountains of water.
Earlier this year a U.S. climate research firm specializing in water science, Eyes on Earth, concluded that China's dams had made a devastating 2019 drought in the lower Mekong basin worse by holding back water despite higher-than-average water levels in China.
China disputed the claim, insisting the upper basin saw less rainfall than usual.
'A bit more transparent'
Goichot said the new data China has promised could help point to the truth.
"If you have access to data all year long then you understand better the operation roles of those dams and you understand if they are improving or aggravating the situation. So for this it makes things a bit more transparent for sure," he said.
And that, he added, can help the lower Mekong countries negotiate tradeoffs with Beijing and try to better balance their losses in fish and farmland with China's gains in generating power.
Not all are convinced the new data will be enough for that.
"That negotiation can only happen if further information about China's upstream dams is shared," said Courtney Weatherby, a research analyst for the Southeast Asia and Energy, Water and Sustainability programs at the Stimson Center, a U.S. think tank.
Of the two dam sites China is sharing data from, only one, the Jinghong, is on the Mekong's mainstream. The Jinghong is the southernmost of the 11 dams on the mainstream in China, and its reservoir is far from the largest.
What Weatherby says the lower Mekong countries really need are more figures from further upstream, where the largest reservoirs lie, including operational data from the dams — how much water they are releasing, and when.
"When you're thinking of China's broad contributions during the wet and dry seasons, it's important to understand how the dams upstream of Jinghong are acting because they're actually the storage. So, they're actually where you're seeing these massive changes in the rise and fall of reservoir levels as water is restricted or released," she said.
"So if the big question is, how are China's dams operating, and how are they withholding water during the wet season and releasing during the dry season, and how is that going to impact the annual flood pulse that downstream countries depend on, that question can't be answered by this new data,” she added.
The natural floods that hit the lower Mekong basin stock many fisheries and nourish the fertile floodplains that have sustained communities there for centuries.
Every wet season in Cambodia, for instance, the floodwaters are counted on to swell fourfold the sprawling Tonle Sap lake, one of the most productive freshwater fisheries in the world. For the past few years, though, droughts have kept the lake at record lows. Experts mostly blame a lack of rainfall but say upstream dams have made the situation worse, a charge China denies.
Tell me more
Weatherby, Lee and Goichot all said the year-round data China will start sharing was a step in the right direction but far from enough to save the Mekong.
Goichot stressed the need for data on how much sediment the dams were letting through. The sediment flowing down the Mekong not only molds the shape, slope and depth of the river but also keeps the delta in Vietnam, the country's rice bowl, from sinking into the South China Sea. At least half that sediment starts out in China's share of the Mekong basin.
But from about the time China started damming the river in the mid-1990s, the river's sediment flows have crashed by 77%, Goichot said citing the commission's data.
Lee said dams along the Mekong mainstream and its tributaries in Laos and Cambodia should share more operating data as well in order to help downstream countries better understand how much their own projects are impacting the river, not only China's.
"As you get further downstream there are more variables at play," he said. "So that's why it's also important for data to be made available from other Mekong governments and developers of large-scale projects in the lower Mekong basin."
