China’s new mega-dam: Should upstream ambitions concern Bangladesh?

When China builds, it usually builds big. 

Take the Three Gorges dam, for instance. Spanning the Yangtze River, the dam reportedly ended up shifting the distribution of the Earth's mass and slowing down its rotation by a short yet measurable 0.06 milliseconds, according to a 2005 estimate by a Nasa scientist.

This time around, it is another megaproject. 

Now, China has decided to build another mega dam along the Yarlung Tsangpo river, expected to be one of the largest such dams in the world. And that has both India and Bangladesh raising eyebrows.

Since the Yarlung Tsangpo river flows into India's Arunachal Pradesh as the Siang, then through Assam as the Brahmaputra, before entering Bangladesh as the Jamuna, the concern is not without merit. 

But according to Sheikh Rokon, founder and secretary-general of Riverine People, Bangladesh may face little risk in terms of water flow, as most of our water comes from rainfall in India. 

"However, my concern is that Bangladesh could become a scapegoat in the water diplomacy between India and China. For instance, India has already hinted at building a counter-dam, which would then directly affect Bangladesh," he said.

In response to China's project, India's plan is to construct a large hydropower dam on the Siang River in Arunachal Pradesh, known as the Siang Upper Multipurpose Project (SUMP).

Dr Ainun Nishat, a water resource and climate change specialist and professor emeritus at BRAC University, believes that first, terms like dam, barrage, etc., must be used correctly, and it is important to understand how a hydropower dam works.

"By storing rainwater in reservoirs, the risk of flooding can be prevented. The water is then released in a controlled way round the year to produce hydroelectricity. That increases the flow downstream during the dry season," he explained.

"We don't have a clear picture of what's happening in China. As the Chinese government clarified that this is solely a hydropower project, it means that the dam will help manage the river's flow — reducing severe monsoon floods downstream and increasing water availability in the dry season. If that is indeed the case, it should be welcomed."

However, he noted that water from the reservoir can be diverted both upstream or downstream if the proponent of the project desires.

"If they divert the flow, it could be a matter of concern for its immediate downstream neighbour, which is India. Because most of the rainfall in the Brahmaputra basin occurs in Arunachal and Assam, not in China.

"The core issue here is about rights. Since the river in China is part of a shared basin with India, Bangladesh, Bhutan, and China, these governments should come together to discuss and negotiate the matter. Creating unnecessary uproar is neither helpful nor desirable," Dr Nishat concluded.

Sheikh Rokon recommends a 'Brahmaputra Commission' comprising all four countries.

Md Moniruzzaman, senior scientific officer at the River Research Institute in Faridpur, also notes that the question is if the river's natural flow will be diverted.

"When such dams are built, downstream countries are naturally put at risk. If the river's natural flow is diverted, the riverbed level rises, the depth decreases, the risk of flooding increases, and riverbank erosion occurs," he said.

It is the transboundary nature of the project that has made it a source of regional unease. Millions of people depend on the river as a water source and for agriculture.

As a lower riparian country, Bangladesh depends heavily on the Brahmaputra for irrigation, navigation and fisheries. Any significant reduction in water flow or sudden release from the dam could affect millions of people, especially during the dry season when the river already faces reduced flow. 

Bangladesh has requested detailed information from China, fearing reduced water flow and potential environmental impacts on the Jamuna river.

Why is India worried?

For India, the primary concern is water security and diplomatic vulnerability.

The Brahmaputra is a lifeline for millions in northeast India, supporting agriculture, fisheries and livelihoods. A massive upstream dam could alter water flow patterns, reduce dry-season availability, and heighten the risk of sudden water releases or floods. 

India fears that China's control over the river could be used as leverage during political or military tensions, effectively 'weaponising water'. 

Moreover, the dam site is close to disputed territory between India and China, adding a geopolitical layer to the concern. Experts also warn of ecological disruptions — sediment flow changes and harm to fragile Himalayan biodiversity — that could impact the entire basin.

A 2020 report published by the Lowy Institute, an Australian-based think tank, noted that "control over these rivers [in the Tibetan Plateau] effectively gives China a chokehold on India's economy".

India's Ministry of External Affairs said in January that it had raised concerns with China and urged Beijing to "ensure that the interests of downstream states are not harmed". 

Arunachal Pradesh Chief Minister Pema Khandu has warned that the dam could "cause an existential threat" to local tribes, saying sudden water releases could devastate communities in the Siang belt.

Beyond water security, both Bangladesh and India fear the precedent China's project sets. As China is not bound by any water-sharing treaty on the Brahmaputra, it can unilaterally build and operate dams, leaving downstream nations vulnerable.

What is China saying?

China has downplayed concerns from India and Bangladesh over the mega dam, insisting the project will not harm downstream countries. 

"The project will not have any negative impact on the downstream regions," Chinese Foreign Ministry spokesperson Guo Jiakun said at a media briefing. 

China also stresses that the project falls within its sovereign rights but pledges to maintain communication with the downstream countries. Jiakun further claimed that China had engaged in "necessary communication" with both India and Bangladesh and continues to cooperate on hydrological data-sharing, flood prevention and disaster mitigation.

Jiakun told Reuters that it is a clean energy initiative aimed at generating massive hydropower, improving flood control, and aiding climate change adaptation, while emphasising that the dam has undergone "rigorous scientific evaluation".

Once completed, the dam is expected to become the world's largest hydropower facility, generating over 300 billion kilowatt-hours of electricity each year — enough to supply power to around 300 million people. According to China's state news agency, the project is expected to cost an estimated 1.2 trillion yuan or $167.1bn.