India is increasingly worried that China's construction of a massive dam on the Yarlung Zangbo River in Tibet could lead to the weaponization of water. According to government analysis, the mega-dam could reduce water flows into India by as much as 85% during the dry season, posing a significant threat to water security.

The Yarlung Zangbo River becomes the Brahmaputra as it enters India, flowing through Arunachal Pradesh and Assam before reaching Bangladesh. This river sustains the lives and livelihoods of over 100 million people across these three nations.

India fears that China, by controlling the river's flow, could use it as a strategic tool, especially considering the existing territorial disputes between the two countries. These concerns are amplified by the absence of a formal water-sharing treaty. While Beijing assures that its hydropower projects are designed not to reduce downstream flows, New Delhi remains skeptical, especially without a binding agreement.

To counter the potential impact of the Chinese dam, India is fast-tracking its own dam project, the Upper Siang Multipurpose Storage Dam in Arunachal Pradesh. This project aims to store water and manage flows to offset disruptions caused by the Chinese dam. The Indian government believes that the Upper Siang dam's storage capacity of 14 billion cubic meters (BCM) would allow them to release water during the dry season, mitigating the impact of reduced flows from the Chinese dam. Without the Upper Siang project, cities like Guwahati could face water shortages of 25%, but with the dam, this loss could be limited to around 11%.

However, India's dam-building efforts have faced resistance from local communities in Arunachal Pradesh. Residents fear that the dam will submerge their villages and destroy their way of life. Environmental experts have also raised concerns about the ecological impact of large-scale damming in the seismically active Himalayas. Building dams in this region could increase the risk of landslides, mudslides, and glacial lake outburst floods.

Despite these concerns, the Chief Minister of Arunachal Pradesh supports the dam, viewing the Chinese project as an existential threat. The state government has stated that the dam will ensure water security and provide flood moderation to counter potential water surges.

Amid these developments, India is also engaging with Bangladesh and Bhutan to build a collective strategy to counter upstream risks. These discussions aim to create a regional framework for water management and address the challenges posed by the changing dynamics of transboundary rivers. S. Jaishankar, India's foreign minister, has raised concerns with his Chinese counterpart regarding the dam. A deputy of Jaishankar also informed lawmakers that the government is taking steps to protect the lives and livelihoods of those living downstream, including constructing the dam.

The situation is further complicated by the lack of transparency and data sharing between India and China. India has not been granted full access to China's hydrological data, which creates distrust, especially during natural disasters or times of tension. Some experts suggest India needs to engage with China to address dam safety and other related concerns.