China’s state news agency recently announced government approval for constructing the world’s largest hydropower project, boasting a generation capacity three times that of the Three Gorges Dam. The proposed mega-dam, to be located on the lower reaches of the Yarlung Tsangpo River, represents an engineering feat of unprecedented scale.
Originating from the Angsi Glacier in the Tibetan Himalayas at an altitude of 5,319 metres, the Yarlung Tsangpo traverses the Tibet Autonomous Region (TAR), where it takes a dramatic turn at the “Great U Bend” before flowing into India as the Siang and eventually becoming the Brahmaputra in India and Jamuna in Bangladesh. Spanning over 3,350 kilometres and crossing four countries (China, India, Bhutan and Bangladesh), the river nourishes the world’s largest delta, hosts unparalleled biodiversity and carves the deepest canyon on Earth.
Given its transboundary nature, any upstream alteration could profoundly impact downstream nations and their ecosystems. China’s plan to build the dam in Medog County, potentially utilising the Yarlung Tsangpo Canyon with its dramatic elevation drop of over 2,000 metres near the U Bend, raises pressing concerns. These include disruptions to water flow, reduced transport of fertile soil downstream, and fears of water diversion for China’s use, which some view as a potential geopolitical weapon under the guise of development.
Impacts on the Brahmaputra
The precise extent of Yarlung Tsangpo’s contribution to the Brahmaputra remains contentious. Existing research presents varying estimates, many of which are outdated. Accurate assessments require up-to-date ground measurements at the river’s tributaries and continuous water flow monitoring across seasons. However, downstream nations face significant challenges due to limited access to upstream data. Geospatial tools and remote sensing offer partial insights into watersheds and precipitation, but comprehensive understanding necessitates detailed on-ground hydrological measurements.
China’s reluctance to share reliable hydrological data with India—particularly after geopolitical standoffs—further exacerbates these challenges. The suspension of data-sharing agreements and non-renewal of Memorandums of Understanding (MoUs) indicate a lack of long-term commitment to transparency. Open-source models calibrated with available data from TAR reveal erratic river flow patterns for 2024, deviating from the past 25 years of observations. These anomalies raise concerns that the river system may already be under stress from natural or human-induced factors. Adding to this uncertainty is the ongoing construction of multiple smaller dams and the proposed mega-dam, complicating efforts to predict downstream impacts.
Vulnerability to climate change and disasters
The Yarlung Tsangpo basin spans five distinct micro-climatic zones as per the Köppen Climate Classification, based on temperature, precipitation, and seasonal variability. Most of the basin experiences a cold, dry mountain climate, while the eastern section after the Great U Bend transitions into a warm, humid tropical monsoon climate with significant rainfall. In the Tibetan Plateau, climate change impacts are expected to vary across these zones, influencing the quality, quantity, flow rate, and seasonal patterns of water reaching downstream areas in India.
The basin’s susceptibility to natural disasters compounds these risks. Landslides and earthquakes pose significant threats, particularly around the proposed dam site,which has high landslide susceptibility. Although flash floods are relatively less frequent in the lower reaches than in the upper reaches, their occurrence cannot be ruled out. Seismic activity remains a persistent danger, with a notable cluster of earthquakes recorded near the U Bend. The recent massive earthquake in Shigatse Tingri (magnitude 7.1) caused deformations in existing dams and surrounding infrastructure, highlighting the precariousness of the region. These factors make the proposed site inherently vulnerable to disasters, raising serious questions about the long-term viability and safety of the project.
What is needed?
Transparency in project planning and execution is paramount to addressing these multifaceted concerns. Clear information about the site, construction methodology, and technologies must be disclosed—such as whether the project involves a reservoir-type or natural flow system. Comprehensive disaster prevention, mitigation, and management strategies are essential to address the inherent risks of natural and climate-induced disasters. Furthermore, measures to minimise environmental and climate change impacts must be prioritised. In addition, the deliberation on the social and cultural implications for Tibetan local populations and communities affected by the project must be disclosed. Regular and transparent sharing of hydrological data with downstream countries is crucial.
As the immediate lower riparian, India may need to address shared concerns with China independently, as Bangladesh is unlikely to collaborate due to its growing alignment with Beijing. Instead, Bangladesh may leverage Indian river dams strategically and align with China, seeking increased water cooperation and support from Beijing.
If China is adamant about harnessing hydropower in the lower reach, ignoring the potential risks to downstream nations and the ecological and geopolitical implications, it must commit to international norms for equitable resource sharing and data exchange at the very least. The Yarlung Tsangpo River is not merely a geographic feature but a lifeline that sustains millions of lives across multiple countries.
(Prof (Dr) Y Nithiyanandam heads the geospatial research programme at the Takshashila Institution, Bengaluru)