The $137 billion project can generate 60 GW of power, but lacks transparency on water storage capacity and environmental impact on millions of people.

In December 2024, China approved construction of a mega hydropower dam on the Yarlung Tsangpo river in Tibet. The river flows into Arunachal Pradesh as the Siang and eventually merges with other rivers to form the Brahmaputra. It then flows into Bangladesh as the Jamuna river.

The new dam proposed to be constructed by China is located across the Great Bend, a dramatic “U” turn the river takes in the Tibetan plateau before flowing into Arunachal Pradesh. The “Great Bend” is in Medog county, known as Pemakoe in the Tibetan language. The region is highly prone to earthquakes given the ongoing collision of the Indian and Eurasian tectonic plates.

China claims the hydropower project is part of its climate ambition to be net-zero by 2060.

The exact design of the dam is as yet unclear, but it is likely that there are five cascading hydroelectric stations that, taken together, can generate 60-70 gigawatts of power. This is thrice the size of the world’s current largest dam: Three Gorges on the Yangtze river in central China.

The other unclear detail relates to the water storage capacity. While officially, the dams could be run-of-the-river, which do not have large reservoirs for storage, they still have the capacity to hold back water to generate power.

Himanshu Thakkar, an engineering and water expert who currently serves as the coordinator of South Asia Network on Dams, Rivers and People (SANDRP) said downstream countries like India and Bangladesh must publicly demand details of basic features of the dam and the standard operating procedures, including the exact dam location, storage capacity (both live and total), dam height from bed and the lowest foundation, and the location and configuration of the power projects. “It is the right of the downstream countries and their people to get this information and it is the duty of the upstream country to provide this. In fact downstream countries can even demand joint impact assessment,” Thakkar added.

The lack of clarity about such details is a big reason why downstream countries like India are worried. Information like water storage capacity in the dam is crucial to ascertain water flows and flooding risks, especially during the monsoon season.

China has not signed any water-sharing treaty with either India or Bangladesh. There are technical arrangements and memoranda of understanding between China and India and Bangladesh to share hydrological data, but these are neither permanent nor binding. During the Doklam standoff in 2017, China briefly stopped sharing water-flow data for Yarlung Tsangpo river with India.

“In times of political crisis or difficult bilateral relations, storage capacity can be used as leverage. And the Himalayan belt is a seismically active part of the world. So, untoward events and accidents could also cause problems to downstream areas,” said Uttam Kumar Sinha, a senior fellow at the Manohar Parrikar Institute for Defence Studies and Analyses, an autonomous body under the Indian Ministry of Defence.

The other concern is that dams hold back silt as well, in addition to water. And agricultural fields in lower riparian regions like Arunachal Pradesh are nourished by silt that flows from the Yarlung Tsangpo. With the construction of a mega dam, silt deposition in downstream areas will also stand reduced significantly. Additionally, the Yarlung Tsangpo flows through one of the most biodiverse and geologically fragile regions in the world.

The Central Tibetan Administration has “deep concerns” about China’s plan to construct the world’s largest project on the lower reaches of the Yarlung Tsangpo in Tibet, Dechen Palmo, a research fellow at the Tibet Policy Institute, told Frontline. Tibet Policy Institute is a research centre of the Central Tibetan Administration, which is the government-in-exile of Tibet based in Dharamshala.

Elaborating on the risks the project poses, Palmo said such large-scale construction in a highly biodiverse and seismically active region raises the possibility of ecological devastation, disruption of wildlife and increased disaster risks downstream.

The area where China plans to build the dam is also culturally significant to Tibetan people. Pemakoe ( པདྨ་བཀོད།) is revered in Tibetan Buddhism as a hidden, lotus-shaped land of Guru Padmasambhava. “A project of this scale will not only threaten traditional ways of life but also risks the forced displacement of Tibetans from their ancestral lands, separating people from the land that has long been central to their identity, culture and spirituality,” Palmo said.

Further, Palmo added, given that Yarlung Tsangpo is a transboundary river, the unilateral decision by China to pursue such a project without consultation or transparency raises concerns for millions of people downstream, particularly in South Asia, where water security is already fragile. “We believe that it is important for the international community and governments to study this project and plan and ensure that the long-term ecological and humanitarian consequences are not overlooked under the guise of green energy development,” Palmo said.

‘What we can do is seek information’

Last month, a spokesperson from the Chinese foreign ministry said China has cooperated with India and Bangladesh on flood prevention and disaster alleviation and has shared hydrological data. India has not refuted the claim. However, further details of the correspondence are not in the public domain.

In response to a question raised in the Rajya Sabha, the Ministry of External Affairs said this month that the Indian government “carefully monitors all developments relating to the Brahmaputra river, including plans by China to develop hydropower projects, and takes necessary measures to protect our interests… As a lower riparian state with considerable established user rights to the waters of the trans-border rivers, Government has consistently conveyed its views and concerns to the Chinese authorities, including on the need for transparency and consultation with downstream countries and has urged them to ensure that the interests of downstream states are not harmed by any activities in upstream areas. The need for cooperation on trans-border rivers, including resumption of provision of hydrological data by the Chinese side has been highlighted by the Government in several bilateral interactions with China including during the recent visit of [External Affairs Minister] to China from July 14-16, 2025 for the [Shanghai Cooperation Organisation] Foreign Ministers’ Meeting.”

But this is a generic response that does not address questions about how exactly India is engaging with China and what information China has shared about the design and operation of the dam. Such information should be placed in the public domain and shared with local people in Arunachal Pradesh who stand to be directly affected by the dam, Thakkar said.

Referring to the meetings held during the visit of the Chinese foreign minister two days ago, the Indian External Affairs Ministry said India has sought “utmost transparency” about the mega dam. However, no further details about the discussions are available in the public domain.

Frontline sent queries to the Chinese embassy in New Delhi seeking basic information about the dam and how China will address concerns of lower riparian countries like India and Bangladesh related to water sharing and flooding. We did not recieve a response.

“The Chinese will build this dam. We have to be real about it. They have their own interests and they will not stop because we are concerned. What we can do is engage with China diplomatically and seek information. Discussions about rivers can be a part of bilateral boundary talks with China. And we can engage with other lower riparian countries like Bhutan and Bangladesh to share concerns about the Brahmaputra. We can also think from an engineering perspective to build storage dams for flood mitigation and hydropower,” Sinha said.

Although there are challenges here too given that large hydropower projects are expensive to build, the region is seismically active and there is local resistance to large hydropower projects.

“Like how Arunachal Pradesh faces flood risks from the Chinese dam, Assam could face flood risks from a dam in Arunachal Pradesh. So, it is the same upper riparian-lower riparian dynamic playing out in India. Engineers will say this is the right approach because we need storage. But there are issues. And there are strong local voices in Arunachal Pradesh raising concerns about safety and resettlement. The other thing we should look at is more scientific flood mitigation efforts in the Northeast and understanding inland waterways to channelise river flows better,” Sinha explained.

News Link: China’s mega dam: Concerns for India and other downstream countries