Chief ministers of Arunachal Pradesh and Assam strongly disagree on whether China’s “Super Dam” will affect the Brahmaputra river’s flow in India. While Pema Khandu has called it a “ticking water bomb”, Himanta Biswa Sarma downplays the fear. Who is right?

While the mega dam will undoubtedly give China the capability of weaponising the water of Brahmaputra (Yarlung Tsangpo in China), it is unlikely to make any consequential alteration to the river flow, according to an analysis by India Today’s Open-Source Intelligence (OSINT) team.

Experts also back the findings of the analysis.

BRAHMAPUTRA’S SUPPORT SYSTEM

Brahmaputra is a complex river system, consisting of several tributaries. Its mainstream traverses a total distance of 2880 km. Out of which, 56 per cent falls in Tibet, 43 per cent in India and 337 km in Bangladesh. The majority (nearly 50.5 per cent) of the Brahmaputra river’s catchment area falls in China.

A river’s flow is sustained by mountain springs, glacial melt, upland wetlands or peat bogs, aquifers, and perennial tributaries. Though most of these sources of water fall in China-controlled Tibet, the Brahmaputra get an estimated 70 per cent of its water from rainfall.

As with many major rivers, Yarlung Tsangpo appears as a stream at its point of origin near Mount Kailash but continues to grow in size further downstream. It becomes the mighty Brahmaputra after absorbing three tributaries, Luhit and Dibang near Assam’s Sadiya.

IMPACT ON INDIA

The contribution of Yarlung Tsangpo to the Brahmaputra’s total flow is barely 10-15 per cent, Dr. Nilanjan Ghosh of Delhi-based Observer Research Foundation (ORF) points out. “So the problem might not be with scarcity but with surplus,” he tells India Today, pointing out the possibility of China suddenly releasing water from the dam to flood areas in India. “Although it is a very remote possibility since it’s a run-of-river project.”

Data shows the river’s annual mean discharge jumps significantly after entering India, indicating that its major sources lie more in India than in China. Some hundred kilometres upstream of the “Super Dam” site, over 31 billion cubic meters (BCM) of water flows annually at Nuxia in Tibet. Its discharge increases to 78 BCM at a point where the river leaves China, further to 185 BCM at Pasighat in Arunachal Pradesh, and 526 BCM in Guwahati’s Pandu, Assam.

Data compiled by researchers Sayanangshu Modak & Nilanjan Ghosh shows the Brahmaputra river basin receives more rainfall in parts falling in India. For example, the mean annual rainfall record at Tibet’s capital Lhasa is pegged at 400 mm, which rises to 767 mm at Tuting near the Tibet border, and 1561 mm in Guwahati.

The diverse precipitation patterns are attributed to factors like climate, altitude, temperature, pressure, latitude and orography. While the northern parts of the Tibetan plateau remain dry, the southern parts received some rainfall due to moisture making its way through the Yarlung Tsangpo Grand Canyon, the deepest on the planet, Chinese researchers wrote in a 2015 paper.

Even during the lean season of November-March, the river’s flows remain significantly higher in India than in Tibet, as per Modak-Ghosh’s research. Moderate rainfall in Arunachal Pradesh during this period keeps recharging the Brahmaputra.

YET, WORRIES REMAIN

Nonetheless, the dam will most likely reduce the Brahmaputra’s flow during peak lean months by around 10 per cent, as per researchers at the Indic Researchers Forum. “Yet, India’s strategic countermeasures, like the Siang Upper Multipurpose Project, can store water to buffer such reductions,” says the forum’s Srinivasan Balakrishnan.

The project is still in the preparation phase and has faced opposition from locals. The government has launched consultations to assuage concerns.

Some also fear that China could divert the river water from the dam to its arid regions in eastwest. Such an effort would require extensive tunnelling through high-altitude plateaus and seismically active zones, a feat described as technically unviable in the foreseeable future due to extreme elevation differences and logistical barriers.

“The dam’s primary design, involving 20-km-long tunnels through the Namjagbarwa peak, focuses on hydropower generation, diverting half the river’s flow for electricity, not large-scale water transfer,” says Balakrishnan.

He also cites a 2017 report that said even pumping water to nearby plateaus was impractical, as it would likely flow back into rivers, not deserts.

– Ends