China has begun building the largest hydropower project on the Yarlung Tsangpo river which becomes the Brahmaputra upon entering Arunachal Pradesh—reviving longstanding Indian concerns about whether Beijing can control how much water reaches India. The project, centered on the river’s “Great Bend” near Medog in Tibet, features five cascade power stations with combined capacity estimated over 60 gigawatts, nearly triple the Three Gorges Dam. Total investment is pegged at 1.2 trillion yuan (roughly $167 billion), making it the world’s biggest infrastructure project. Over 30 miles, the river drops nearly 6,500 feet—one of Earth’s steepest descents. China plans to divert the river through multiple tunnels, some longer than 12 miles, feeding cascade stations rather than storing water behind a single dam.
Indian government analysis has flagged the possibility of dry-season flows falling by as much as 85%. Chinese authorities have consistently rejected suggestions the project poses risks to downstream countries, with the Foreign Ministry stating the project underwent decades of scientific studies and environmental assessments. Hydrologists note China cannot permanently stop the Brahmaputra from flowing into India because the river receives substantial additional water from monsoon rainfall and tributaries after entering Arunachal Pradesh and Assam. However, a massive upstream reservoir would enable China to regulate the timing and volume of water releases. China’s project has been described as a hydropower dam rather than a diversion scheme; run-of-the-river projects generally release water downstream after generating electricity, though reservoirs can alter seasonal flows.
New Delhi increasingly views the project through national security, since the river flows through Arunachal Pradesh, which China claims as “South Tibet.” Arunachal Pradesh Chief Minister Pema Khandu described the project as a potential “water bomb”, warning flows could “dry up considerably” during reservoir filling and sudden releases could increase flood risks. There is an absence of comprehensive water-sharing treaty governing the Brahmaputra between India and China. A study by Chinese geologists identified an active fault line beneath the construction site that could undermine dam stability, contrasting with Beijing’s assertions about highest safety standards.
India has fast-tracked its own answer: the Siang Upper Multipurpose Project (SUMP), an 11,000 MW hydroelectric and flood-control mega-dam proposed on the Siang river in Arunachal Pradesh. Driven by state-run NHPC, SUMP would become India’s largest hydropower project if built, generating an estimated 47 billion units of electricity annually at a projected cost of approximately US$13 billion.
