However, these arguments coexist with an acknowledgement: The Brahmaputra River Basin remains one of the most under-researched river systems in the world. This supports the uncomfortable truth that the scientific understanding of the basin remains woefully inadequate. In the face of such uncertainties, is it reasonable to assert that the dam will have “no impact” or dismiss biophysical and human concerns as media sensationalism?

Despite its robust models and extensive research, even the Intergovernmental Panel on Climate Change (IPCC) avoids making absolute claims. Science thrives on probabilistic reasoning, preparing policymakers for various possible outcomes. Shouldn’t we, as scientists, exercise similar caution and rigour before drawing definitive conclusions such as “no impacts”?

The challenges of climate variability

The lack of scientific understanding of the Brahmaputra raises a pressing question: If there is no conclusive evidence to suggest that upstream dams will cause the river to dry up, is there sufficient data to claim it will remain unaffected? This uncertainty is particularly critical given the erratic impacts of climate change.

Although the Brahmaputra benefits from abundant annual precipitation, shifting precipitation patterns introduce complexities that require deeper research. A recent study published in Water Conservation Science and Engineering (2024), which examined precipitation extremes in the Brahmaputra River Basin using NEX-GDDP datasets, reveals notable shifts in precipitation patterns across the region. In the upper Brahmaputra region (Tibet), consecutive wet days are projected to increase, leading to intense rainfall and heightened flood risks. Conversely, the lower basin (Assam) is likely to face more consecutive dry days, resulting in prolonged dry spells. These projections challenge the assumption that precipitation patterns will remain stable.

In this context, India’s dependence on upstream China is set to grow. During the wet season, uncoordinated water releases from Chinese dams could exacerbate flooding in downstream regions like Assam and Bangladesh, particularly during the monsoon. For China, such releases would enhance power generation, but for downstream communities, they would mean heightened flood risks. During the dry season, extended dry spells downstream would increase reliance on upstream water releases, complicating water management efforts. Research conducted under RCP 4.5 and RCP 8.5 climate scenarios underscores these challenges and highlights the urgent need for collaborative water governance and robust scientific investigation.

Geopolitical and ecological implications

The Medog Dam is touted as a run-of-the-river project with minimal downstream impact. Yet, China’s lack of transparency and halted data sharing prevent India and Bangladesh from verifying these claims. The 2023 expiry of the India-China hydrological data-sharing agreement — crucial for flood preparedness in downstream states like Assam — adds to the uncertainty, with little public discussion on its renewal or improvement.

Assam, already hit by pre-monsoon floods affecting nearly 7 lakh people, faces heightened vulnerability without timely data. The 2017 Doklam crisis showed the consequences of China’s discontinuation of sharing hydrological information, coinciding with severe Assam floods. Without reliable data, flood forecasting and preparedness is difficult, leaving millions exposed. Robust data-sharing and transparency are essential for managing this fragile river system.

Beyond flow concerns, the dam’s location in Medog County — a seismically active zone and epicentre of the 1950 Assam-Tibet earthquake that altered the Brahmaputra’s course — raises serious safety questions. Situated on a major tectonic fault, the dam faces high structural risks. Building without thorough geomorphological, seismic, and hydrological studies would be reckless, threatening not only the dam but also millions downstream.

China must be held accountable to ensure that downstream nations know how dam safety will be guaranteed through joint research for the entire basin. International cooperation and transparency are critical to prevent potentially catastrophic impacts on this vital and vulnerable region.

The overlooked role of glaciers

Another critical yet under-discussed aspect is the role of glacier meltwater in sustaining the Brahmaputra’s flows, especially during the dry seasons. Originating from glaciers in the Tibetan Plateau, these glaciers act as natural reservoirs, supporting irrigation, hydropower, and ecosystems. However, the contribution of glacier meltwater to the river system remains poorly quantified. Without precise data on the volume of water stored in these glaciers and their seasonal melt contributions, it is challenging to plan effectively for future water availability.

Further, the long-term impacts of climate change on these glaciers will not remain static, further complicating the dynamics of glacier melt runoff to the Brahmaputra River. The health of these glaciers depends largely on their mass balance, which is influenced by precipitation in the form of snowfall at high altitudes. Understanding the variability of future solid precipitation in the basin requires robust scientific expertise to assess the glaciers’ health and their evolving role in sustaining the river’s flow. Addressing these knowledge gaps is vital to developing adaptive water management strategies for the Brahmaputra basin in the face of a changing climate.

Current debates often emphasise monsoon-fed systems, overlooking the critical role of dry-season flows sustained by glacier melt. This omission leaves significant gaps in understanding the river’s year-round dynamics. To claim that the Tibetan glaciers have no role whatsoever in sustaining the Brahmaputra’s flows is, at best, an understatement, given the limited knowledge and data available on this aspect.

The way forward

The Medog Dam underscores the urgent need for transparency, cooperation, and comprehensive research. Downstream nations must push for multilateral negotiations on data-sharing and joint research to explain the basin-wide impacts of water infrastructure. Instead of dismissing concerns about China’s dam projects, India and Bangladesh should seek alliances to advocate for collaborative management of the Brahmaputra River Basin.

The stakes are too high to ignore. Without robust science and cooperative frameworks, the Medog Dam may become not just a marvel of engineering but a flashpoint for environmental, geopolitical, and social disasters. The scientific community needs to refrain from creating lop-sided narratives of “no impact” as this could undermine India’s negotiating position with China. Instead, we must promote an evidence-based narrative that water infrastructure on the Brahmaputra will be the point of conflict in the near future.

We must accept the future challenges and start working towards science to develop a negotiated solution portfolio for the next generation of South Asia.

Anamika Barua is Professor, Indian Institute of Technology Guwahati; Sumit Vij is Assistant Professor, Wageningen University, the Netherlands; Ashim Sattar, Assistant Professor, Indian Institute of Technology Bhubaneshwar