China’s ambitious South-to-North Water Diversion Project, the world’s largest water transfer scheme at approximately 500-700 billion yuan (over US$70 billion) in investment, poses escalating risks to Bangladesh and Southeast Asian nations by fundamentally altering flow patterns in shared rivers including the Brahmaputra and Mekong.
Conceived by Mao Zedong in 1952 after a visit to the Yellow River, the project reflects China’s fundamental geographic water imbalance: the Yangtze River Basin and southern regions account for over 80 percent of China’s national water runoff but contain only 35 percent of cultivated land, while northern basins account for only six percent of runoff but 40 percent of cultivated land.
After nearly half a century of analysis and comparison across more than 50 proposals, China finalized a three-route diversion scheme. The eastern route, completed in 2013, diverts 14.8 billion cubic meters annually from the lower Yangtze using existing channels, including the ancient Beijing–Hangzhou Grand Canal. The central route, completed in 2014, transfers 13 billion cubic meters from the Danjiankou Reservoir northward through gravitational flow to Beijing and Tianjin, supplying 19 major cities and over 100 counties. When fully operational, these two routes will collectively transfer approximately 27.8 billion cubic meters annually to northern China.
It is the western route that presents serious transboundary consequences. Designed to transfer 17 billion cubic meters annually, it diverts water from the Yangtze and its tributaries (including the Tongtian, Yalong and Dadu) across the Bayan Har Mountains watershed through tunnel excavation. However, research by China’s water science establishment indicates expanded proposals that also target the Yarlung Tsangpo (Brahmaputra), Lancang (Mekong) and Salween rivers originating on the Tibetan Plateau.
The state-owned China South-to-North Water Diversion Company reported that by December 2024, the completed eastern and central routes had cumulatively diverted over 750 billion cubic meters since operations started—an extraordinary hydrological manipulation. Construction is projected to take another 40-50 years for full completion of all three routes.
Bangladesh’s existential water vulnerability
Bangladesh confronts transboundary water insecurity as an existential challenge rather than a policy matter. The UN notes that 90 percent of the nation’s water resources originate outside its borders. In a fundamental asymmetry, Bangladesh contributes none of the upstream areas yet depends entirely on downstream flows for agricultural production, fisheries and drinking water.
Recent research documents the concrete impact of upstream interventions on Bangladesh’s delta. According to the UN Environment Programme and international sediment specialists, if Bangladesh wants to offset rising sea levels, the “principal nature-based solution” is the unabated delivery of the Ganges-Brahmaputra’s sediment load of approximately 1 billion tons per year. And this faces catastrophic risk from proposed upstream dams and diversions.
For a nation where the delta constitutes over 80 percent of habitable territory and where “the implementation of currently proposed dams and diversions would preclude such opportunities” for natural sustenance, this is an existential threat.
Bangladesh’s accession this year to the UN Convention on the Law of Non-Navigational Uses of International Watercourses came because traditional bilateral arrangements have failed to protect downstream water security from upstream megaprojects. But this convention’s effectiveness, too, depends on universal participation, i.e. it cannot work without China, which has historically rejected any internationally binding water-governance frameworks.
Mekong crisis
The Lower Mekong Basin supports over 60 million people whose livelihoods depend on fisheries, agriculture and hydroelectric generation powered by monsoon-driven flows. The Mekong River Commission, established through the 1995 Mekong Agreement among Cambodia, Laos, Thailand and Vietnam, provides the institutional framework for cooperative basin management. Yet China, despite controlling over 90 percent of the basin’s hydrological storage capacity through dams in Yunnan Province, remains outside this structure.
China operates 11 major dams along the Mekong mainstream (called Lancang in Chinese territory) and 95 subsidiary dams within its territory, according to international monitoring systems. Two mega-dams—Xiaowan (completed 2010) and Nuozhadu (completed 2012)—have a collective storage capacity equivalent to approximately half the basin’s entire usable water resources. This physical infrastructure grants China extraordinary unilateral control over downstream water availability, sediment transport, and seasonal flow patterns.
Vietnam, the delta nation most vulnerable to water scarcity, has suffered a continuous drought since 2019, the longest in recorded history. A 2016 drought, when the Mekong reached its lowest level in 90 years, caused saltwater intrusion across 13 Vietnamese provinces, salinizing agricultural lands, destroying fisheries, and costing the delta economy approximately $100,000 daily in lost productivity.
Similar effects strike Thailand, where irrigation fails during the dry season, Cambodia, where the Tonle Sap lake’s fish populations crash as altered flow patterns reduce the lake’s natural seasonal expansion, and Laos, which depends on dam revenues while confronting international criticism for permitting subsidiary dam construction.
The Tibetan Plateau, then, is Asia’s hydrological heart, with eight major river systems originating in this high-altitude region—and the Chinese government has identified no fewer than 193 hydropower projects across Tibet at various stages of development. (Environmental impact assessment documents reveal fundamental deficiencies in evaluation procedures and community participation.)
The Medog megadam
China’s authorization in December 2024 of the Medog (Motuo) hydropower station marked an explicit commitment to this controversial western route. State-owned PowerChina will build the facility, at a capacity of 60,000 MW the world’s largest hydropower installation. It sits at the dramatic Great Bend of the Yarlung Tsangpo in Tibet’s Nyingtri Prefecture, precisely where the river changes course toward India’s Arunachal Pradesh.
The project will “divert a large share of the river’s flow, partially dewatering nearly 200 km of China’s Yarlung Tsangpo Canyon.” With an estimated investment exceeding 1 trillion yuan (approximately $137 billion) and planned commercial operations for 2033, it dwarfs all previous upstream interventions.
Strategic vulnerability
China’s water management strategy reflects a coherent geopolitical vision: water is a strategic commodity that serves China’s developmental requirements while simultaneously conferring leverage over neighboring nations that depend on transboundary flows. The South-to-North Water Diversion Project, interpreted alongside Tibet’s hydropower expansion, is a systematic exercise of upstream hydrological control.
Bangladesh and Southeast Asian nations confront their strategic vulnerability without hydrological control mechanisms, binding agreements guaranteeing minimum flows, or consultative authority over upstream construction.
Immediate multilateral action is required. It should aim to renew and expand hydrological data-sharing agreements with transparent, real-time access. China must be persuaded to ratify the UN Watercourses Convention, while binding regional agreements must be struck that incorporate flood management, flow maintenance, and environmental protection principles. And transparent environmental impact assessment procedures are needed, with genuine community participation as documented by China’s own research institutions. Climate change intensifies water scarcity across Asia. Without comprehensive multilateral water governance frameworks, lower riparian nations will remain hostage to water decisions made unilaterally in Beijing.
Chandu Doddi is a research scholar in Chinese Studies at the Centre for East Asian Studies, School of International Studies, Jawaharlal Nehru University (New Delhi).
