The Yarlung Tsangpo flows from Tibet into Arunachal Pradesh. The biggest concern may ultimately be geological. 7, remains a stark reminder of the region’s seismic potential.

The Chinese geological study has added to concerns over the site.

“Ironically, the latest evidence suggests that China's scientific establishment understands the dangers of building the unprecedented super-dam more clearly than its political leadership appears willing to acknowledge.

There are also concerns about the possibility of reservoir-triggered seismicity, in which the weight of water stored behind a large dam can affect pressure and stress along existing faults.

The concern, therefore, is not only whether an earthquake could damage the dam. “Modern engineering can design dams to withstand very strong earthquakes. Advanced materials, flexible structural designs and continuous monitoring systems have greatly improved dam safety.

The region has also witnessed glacier collapses and landslides. The August 26 disaster in Nepal offers a stark example of how Himalayan hazards can interact. The avalanche reportedly travelled at around 50 metres per second.

The 2015 Nepal earthquake provided another warning. How climate change is adding to the riskClimate change is adding another layer of uncertainty to an already fragile landscape. Glaciers across the Hindu Kush Himalaya are losing ice, while permafrost degradation can destabilise high-altitude slopes.

Climate change does not cause every landslide, avalanche or flood. Floodwaters are discharged from other dam. (Xinhua News Agency) The ecological concernsThe Medog project is being built in an exceptionally sensitive landscape.

The impact of such a project is also unlikely to be limited to the dam itself. The project’s location also raises questions about its strategic implications for India. The concern is not simply that the dam could alter river flows.

“Such a large project requires roads, tunnels, bridges, power infrastructure and communication networks. Some analysts, however, see the project as giving Beijing additional diplomatic leverage because of its upstream position. Others take a more cautious view.

Dam can affect Earth’s rotationEarth’s rotation is not perfectly constant. Natural forces such as earthquakes, the Moon’s gravitational pull, melting ice and the movement of water can subtly change how quickly the planet spins. China’s Three Gorges Dam provides one striking example.

When its vast reservoir is filled, the enormous volume of stored water redistributes mass on Earth. The change is far too small to have any noticeable effect on everyday life. China calls Brahmaputra project safeBeijing has repeatedly sought to reassure downstream countries about the safety of the Medog project.

A Chinese foreign ministry spokesperson said China was highly responsible in developing cross-border rivers and had extensive experience in hydropower construction.

The recent geological study does not necessarily contradict those assurances in the sense of proving that the dam is unsafe.

The problem of hydrological dataFor India, one of the most important lessons from the past is the importance of reliable river-flow information.

In a written reply in the Rajya Sabha on February 8, 2018, the Ministry of External Affairs said China had not provided hydrological information on the Brahmaputra and Sutlej despite existing bilateral agreements.

China resumed Brahmaputra hydrological data sharing in May 2018.

For India and Bangladesh, the challenge is therefore broader than whether China can control the Brahmaputra.

For India, the Medog project is therefore not just a question of water. A glacier can collapse. Rock can fall into a river.

A temporary blockage can form. The blockage can breach. When roads, bridges, tunnels, hydropower plants and settlements occupy that same valley, the consequences multiply.

The issue is not whether Nepal, India or China should develop their mountain regions. China's Yarlung Tsangpo project therefore represents more than a massive power-generation scheme. The Himalayas are already under pressure from climate change, earthquakes, landslides, glacier retreat and intense rainfall.

The immediate cause of Nepal's August 26 disaster may have been a glacier-rock collapse. The Brahmaputra does not recognise borders. Neither do earthquakes, glaciers, landslides or extreme weather.

As construction of the Medog project advances, the questions will become increasingly difficult to avoid: Can the world's largest hydropower project remain safe in one of the world's most geologically active landscapes? For now, there are no easy answers. But the floods in Nepal have made one thing clear.

In the Himalayas, the consequences of getting the balance between development and nature wrong can travel far beyond the valley where the decision was made.

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