Hydropower dams represent significant engineering achievements with far-reaching implications, but they also spark debates due to their environmental, socio-economic, and geopolitical impacts. These dams serve as crucial sources of renewable energy, contributing to economic development and energy security in target areas. They can also exacerbate water security issues for neighbouring countries that are reliant upon those critical natural resources while potentially yielding negative externalities related to sediment transport, ecosystem sustainment, and downstream water flow.
For all the many potential sources of risk and opportunity in South and Southeast Asia, dam construction on the Brahmaputra and Mekong Rivers represents one of the most important but least understood activities. Multiple governments are actively implementing projects aimed at increasing the already extensive dam networks, which—although supporting local populations—may have unintended consequences for those downstream. While there have been some diplomatic efforts to manage those consequences, the rapidly expanding dam networks in the region demand more work on that front.
Background
The hydrological landscape of Asia is focalised on Tibet, which serves as the origin of rivers extending downstream to several countries in South and Southeast Asia. This dominance is a consequence of China’s control over the water-abundant Tibetan Plateau. It is commonly referred to as “The Third Pole,” “The Water Tower of Asia,” “The Roof of the World,” and “The Barometer of Asia,” as this region encompasses pivotal rivers such as the Indus River (Senge Tsangpo), Brahmaputra River (Yarlung Tsangpo), Mekong River (Zachu), Yangtze River (Drichu), Yellow River (Machu), Salween River (Gyalmo Ngulchu), and Ganges. Approximately 2 billion people rely on major rivers originating from the Tibetan Plateau, underscoring its significance.
Several of Asia’s major rivers extend from the Tibetan Plateau (Source: The National Bureau of Asian Research)
In South Asia, the Brahmaputra River, one of the major rivers of the world, originates in the Himalayas and flows through China, India, and Bangladesh. It spans approximately 2,900 kilometres, providing water to millions and supporting diverse ecosystems. The river’s significance lies not only in its ecological importance but also in its contribution to agriculture, fisheries, and transportation. However, the Brahmaputra faces challenges such as seasonal flooding, sedimentation, and ever-increasing pressure from developmental projects, including hydropower dams.
Meanwhile, in Southeast Asia, the Mekong River flows through six countries—China, Myanmar, Laos, Thailand, Cambodia, and Vietnam—and is vital to Southeast Asia. Covering a distance of about 4,350 kilometres, it sustains one of the world’s most productive inland fisheries and supports the livelihoods of over 60 million people. The Mekong’s rich biodiversity and ties to cultural heritage are threatened by extensive dam construction, which impacts water flow, sediment transport, and aquatic ecosystems.
Table 1: Key Transboundary Rivers Brahmaputra and Mekong
River Name | Origin | Length (Km) | Basin Area (sq. km) | Countries Shared | Major Uses |
Brahmaputra | Tibet (China) | 2,900 | 580,000 | China, India, Bhutan, Bangladesh | Hydropower, Irrigation |
Mekong | Tibet (China) | 4,350 | 795,000 | China, Myanmar, Laos, Thailand, Cambodia, Vietnam | Hydropower, Navigation |
Source: Author’s compilation; data available here.
Hydroelectric Dams in South and Southeast Asia
Hydropower in South Asia and Southeast Asia has enormous potential on both a large and small scale to address regional energy requirements. These dams harness the energy of flowing water to generate electricity. They are categorised into different types, including run-of-the-river, reservoir, and pumped storage dams. Their structures offer numerous benefits, such as renewable energy production, flood control, and water supply management. Their construction has led to significant environmental and social changes.
Several key hydropower dams on the Brahmaputra have been proposed or constructed. This includes the Zangmu Dam in China which has been operational since 2015, is considered the first dam China built on Brahmaputra, and has capacity of 510 MW. As a part of China’s 14th Five-Year Plan, the government proposed a “super dam” in Tibet’s Medog county, which is expected to generate 60 MW. Apart from those, there are other dams including the Dagu (640 MW), Jiexu (560 MW), and Jiacha (320 MW), all of which are part of a broader plan to harness the hydropower potential of the region. This is all in addition to China’s expansive dam network which includes the world’s largest dam—the “Three Gorges Dam”— and about 87,000 small dams.
Activity on the Indian side is also robust. The Subansiri lower dam is planned to generate 2,000 MW and counteract the impact of Chinese dams on the Brahmaputra flow. Similarly, Yingkiong dam is also planned to be built in Arunachal Pradesh to store 10 billion cubic metres of water providing both hydropower and flood control. According to government sources, India intends to invest $1 billion to speed the building of 12 hydropower units in Arunachal Pradesh. The Indian finance ministry recently sanctioned financial support of up to 7.5 billion rupees ($89.85 million) for each hydropower project in the northeastern area. Moreover, in the last 20 years, India has constructed hydropower facilities with a capacity of fewer than 15 gigawatts.
The Three Gorges Dam in 2021 (photo via Wikimedia Commons)
On 9 March 2024, Prime Minister Modi inaugurated the foundation stone of the 2,880 MW Dibang Multipurpose Hydropower Project by NHPC Limited in the Lower Dibang Valley district of Arunachal Pradesh. This event took place during the “Viksit Bharat Viksit North East Program” in Itanagar, Arunachal Pradesh. There, Modi announced that “the Dibang dam will be India’s highest dam,” emphasising the dedication of both the highest bridge and the highest dam to the Northeast region. It is set to generate 11,223 million units of clean and green energy annually, which will be integrated into the Northern Grid. The construction of the project is expected to span 108 months, with a planned commissioning date in February 2032.
Meanwhile, the Mekong River also hosts numerous large dams. China operates a series of 11 major dams on the Upper Mekong, known as the Lancang in China. These dams include Xiaowan dam as one of the largest dams on the river, which can store up to 15 billion cubic meters of water and generate 4,200 MW of electricity. Nuozhadu dam is another significant dam with a storage capacity of 22.7 billion cubic meters and an output of 5,850 MW. Jinghong dam, with a capacity of 1,750 MW, significantly affects water flow downstream. These dams are crucial for China’s energy strategy but have been criticised for their impact on downstream water flow, sediment transport, and ecosystem health, particularly in Laos, Thailand, Cambodia, and Vietnam.
Laos has also embarked on an ambitious hydropower development program, with numerous dams constructed or planned, aiming to become the “Battery of Southeast Asia.” Xayaburi Dam was the first dam on the lower Mekong mainstream, operational since 2019, with a capacity of 1,285 MW. Don Sahong Dam is located near the Laos-Cambodia border and has been operational since 2020, generating 260 MW. Pak Lay and Pak Beng Dams are still in the planning stages with projected capacities of 770 MW and 912 MW respectively, and they are expected to significantly impact local communities and ecosystems.
Managing the geopolitical implications
The construction of hydropower dams on transboundary rivers like the Brahmaputra and Mekong has geopolitical ramifications. Water rights disputes arise between upstream and downstream countries, affecting international relations. For instance, China’s upstream dam projects on the Brahmaputra have raised concerns in India and Bangladesh about reduced water flow and ecological impacts. Similarly, Mekong dam projects have led to tensions among Southeast Asian nations.
Transboundary river management requires international cooperation and the establishment of legal frameworks for water sharing. Treaties and agreements facilitate the equitable distribution of water resources and promote joint efforts in addressing environmental challenges. Organizations like the Mekong River Commission (MRC) play a pivotal role in fostering dialogue and collaboration among riparian states. Strengthening these cooperative mechanisms ensures sustainable development and regional harmony.
During heavy rainfall, upstream countries holding the dams have the ability to release water, which often results in flooding downstream if not managed effectively. Effective communication and timely notifications are critical for mitigating the risks of unexpected water release. Establishing bilateral or multilateral agreements that require early warnings and transparent communication will help downstream countries prepare for and respond to impending floods.For example, India and China have set up a real-time data-sharing network to alert downstream areas of impending water releases from Brahmaputra River dams. Such alerts enable downstream countries such as Bangladesh to take the required safeguards and manage water flow, thus reducing the danger of catastrophic flooding. For example, one Memorandum of Understanding between the two governments provides for a direct information exchange mechanism and requires China to give India hydrological data (including water level, discharge, and rainfall) for three Yarlung stations in Tibet: Nugesha, Yangcun, and Nuxia. This information is delivered twice daily, at 08:00 and 20:00 (Beijing Time), from 15 May to 15 October each year.
Table 2: Discharge at Various Sites on the Yarlung Tsangpo, Siang, Brahmaputra, and Jamuna Rivers
Stretch | Observation Site | Mean Annual Discharge (in BCM) |
Yarlung Tsangpo | Nuxia | 31.2 |
Yarlung Tsangpo | Point leaving China | 135.9 / 78.10 |
Siang | Pasighat | 185.1 |
Brahmaputra | Bechamara, Majuli | 278.4 |
Brahmaputra | Pandu | 526.1 |
Jamuna | Bahadurabad | 605.49 |
In addition to managing excess water during rainy seasons, downstream countries may require additional water in periods of drought or low precipitation to support agricultural, drinking water supply, and hydropower generation. A formalized request system integrated into international water-sharing agreements could help meet these objectives. For example, downstream governments may seek to release stored water from upstream dams during those critical periods as long as these requests are jointly agreed upon and handled to avoid harm to the upstream country's water security.The development of hydroelectric dams also creates chances for power sharing, which may counterbalance some of the possible negative consequences. Upstream dam operators can create regional cooperation and goodwill by sharing their electricity with neighbouring countries. For example, with its large hydropower resources on the Mekong River, Laos has emerged as a big electricity exporter to neighbouring Thailand and Vietnam. Such power-sharing arrangements not only help to ensure regional energy security but also give economic incentives for collaboration.
There are many more questions yet to be answered, but hydropower dams on the Brahmaputra and Mekong rivers are inevitably demonstrating the complex interplay between development and water security. While these projects will yield significant benefits in terms of renewable energy and economic growth, they may also pose substantial challenges to geopolitical stability. Balancing the needs of energy production with ecological preservation, social equity, and international relations requires innovative solutions, collaborative efforts, and a commitment to sustainable development. The future of hydropower development on the Brahmaputra and Mekong hinges on sustainable practices and international cooperation, and the issue of dam construction in these regions remains a critical focal point for observation.
Neeraj Singh Manhas is Special Advisor for South Asia at the Parley Policy Initiative, Republic of Korea. He has authored and edited six books and has various research interests covering Sino-Indian border issues; Transboundary Rivers; Water security; and Defence studies. He tweets on X (formerly Twitter) as @The_China_Chap.