Published on: August 26, 2025 9:42 AM
India fears a planned Chinese mega dam in Tibet will reduce water flows on a major river by up to 85 percent during the dry season, according to four sources familiar with the matter and a government analysis seen by Reuters, prompting Delhi to fast-track plans for its own dam to mitigate the effects.
The Indian government has been considering projects since the early 2000s to control the flow of water from Tibet’s Angsi Glacier, which sustains more than 100 million people downstream in China, India and Bangladesh. But the plans have been hindered by fierce and occasionally violent resistance from residents of the border state of Arunachal Pradesh, who fear their villages will be submerged and way of life destroyed by any dam.
Then in December, China announced that it would build the world’s largest hydropower dam in a border county just before the Yarlung Zangbo river crosses into India. That triggered fears in New Delhi that its longtime strategic rival – which has some territorial claims in Arunachal Pradesh – could weaponize its control of the river, which originates in the Angsi Glacier and is known as the Siang and Brahmaputra in India.
India’s largest hydropower company in May moved survey materials under armed police protection near a prospective site of the Upper Siang Multipurpose Storage Dam, which would be the country’s biggest dam, if completed. Senior Indian officials have also been holding meetings about accelerating construction this year, including one organized in July by Prime Minister Narendra Modi’s office, according to two of the sources, who spoke on condition of anonymity to discuss sensitive government matters.
Delhi’s concerns were described in the undated Indian government analysis of the Chinese dam’s impact, the specifics of which Reuters corroborated with four sources and is reporting for the first time.
Beijing hasn’t released detailed plans about the dam’s construction, but the analysis drew on past work conducted by Indian government-affiliated institutions like the Central Water Commission and accounted for the expected size of the Chinese project, which broke ground in July and will cost nearly $170 billion.
Delhi estimates the Chinese dam will allow Beijing to divert as much as 40 billion cubic meters of water, or just over a third of what is received annually at a key border point, according to the sources and the document. The impact would be especially acute in the non-monsoon months, when temperatures rise and lands become barren across swathes of India. The Upper Siang project would alleviate that with its projected 14 BCM of storage capacity, allowing India to release water during the dry season.
That could mean the major regional city of Guwahati, which is dependent on water-intensive industry and farming, would see a reduction in supply of 11 percent, according to the sources and the document, as opposed to 25 percent if the Indian dam isn’t built.
The project could also mitigate any move by Beijing to release devastating torrents of water downstream, the sources said. If the dam is at its minimum drawdown level – where water is stored at less than 50 percent of its height – it would be able to fully absorb any excess water released from a breach in Chinese infrastructure, according to the document and the sources. India is considering a proposal to keep 30 percent of its dam empty at any time in order to account for unexpected surges, two of the sources said.
