By Pooja Gupta
The Siang Upper Multipurpose Project (SUMP), proposed near Upper Siang district in Arunachal Pradesh, is set to be India’s largest hydropower dam – a nearly 11,000 MW structure conceived to regulate flow on the Siang River, which becomes the Brahmaputra downstream in Assam. It is also one of the most intriguing question facing the Northeast today, because it sits at the meeting point of three legitimate concerns that do not resolve easily into one another: national water security, the wellbeing of the Adi and Galo communities who call this valley home, and India’s strategic position vis-à-vis China’s upstream dam-building on the Yarlung Tsangpo.
Why the project matters
The case for SUMP begins upstream, in Tibet. China started construction in mid-2025 on the Medog Hydropower Station, a five-dam cascade at the Yarlung Tsangpo’s dramatic “Great Bend,” with a planned capacity of roughly 60,000 MW – nearly three times that of the Three Gorges Dam. China is not a signatory to any binding international water-sharing treaty, and hydrological data-sharing with India has been inconsistent in the past. For a river system that close to a billion people ultimately depend on downstream, that combination of scale and uncertainty is a genuine planning concern, not an exaggerated one.
The Siang Upper Multipurpose Project (SUMP) is basically expected to serve the following three purposes: regulating the Siang’s flow so that unusual releases from upstream do not translate into flash flooding for Arunachal Pradesh and Assam; establishing India’s own substantial water infrastructure and prior-use position on a river with no formal treaty; and generating clean power for a north-eastern grid that badly needs it, with a share of free electricity promised to the state. Arunachal Pradesh Chief Minister Pema Khandu has described the project in these terms – as an insurance policy against unpredictability upstream, built at a time when India cannot simply wait for a bilateral water-sharing arrangement that may be years away.
The concerns that deserve equal weight
At the same time, the project’s scale is significant enough that the concerns raised by local communities are not a footnote to the national story – they are a central part of it. Estimates of how many villages and people would be affected have varied as the project has evolved, ranging from roughly a dozen submerged villages in earlier assessments to newer estimates by the Siang Indigenous Farmers’ Forum (SIFF) of around 27 villages and well over 100,000 people whose land, homes or farming livelihoods would be touched in some way. For a community where agriculture is the primary occupation, and where land carries cultural as well as economic weight, that is a substantial ask to make of any population.
Consultation has been a genuine point of friction. Village-level agreements have been signed at various stages – most recently in March 2026, when families from Simong and Halleng villages backed the project’s preliminary survey stage – and these are a positive sign that engagement is possible. But other agreements have been disputed by residents of the same villages, and the Adi Bane Kebang, the community’s apex traditional body, has taken a firmer position against the project as currently framed. Deployment of central security personnel to facilitate survey work in 2025 also drew strong local pushback, a reminder that for a project of this scale, the manner of consultation matters almost as much as its content. None of this is a case against the dam itself; it is a case for slowing down the process enough that consent is unambiguous and durable, rather than contested at every stage.
What the valley’s knowledge systems bring to the table
One dimension of this debate that deserves more attention than it usually gets is what the Siang valley’s own accumulated knowledge contributes to exactly the problem SUMP is trying to solve. The Adi and Galo communities have developed, over generations, a detailed working knowledge of this river system – a winter fishing method called Lipum, built around stone structures placed with an intimate understanding of seasonal flow and sediment behaviour; an elaborate terraced wet-rice cultivation and irrigation system engineered largely by hand; and a documented reliance on more than 250 species of wild plants and animals for food, medicine and cultural use.
A concrete example, recorded in field research on Adi biocultural knowledge, illustrates how specific this knowledge is. Otek Moyong, an Adi knowledge-holder from the region documented for her expertise in local biodiversity, described how a particular insect found among the rocks and moist riverbank sand near the Siang is read as a seasonal signal: if it takes flight around sunset, it is taken to indicate a good rainfall year ahead, and farmers respond by planting taller paddy varieties suited to wetter conditions. It is a small, precise, locally calibrated forecasting practice, developed long before formal weather monitoring reached this valley – and, notably, one whose insect habitat has already been reported as vulnerable to disturbance from construction activity along the riverbank. This is not an isolated example; it is representative of the kind of granular, tested knowledge held across the valley, in the form of similar seasonal indicators, planting calendars and land-use practices that formal climate-adaptation planning in the Northeast is only beginning to document.
That knowledge is directly relevant to the climate-risk conversation SUMP is meant to be part of. Independent reviews of the project site have flagged growing concern about Glacial Lake Outburst Floods (GLOFs) and broader climate-driven instability in the upper catchment – the kind of risk that damaged the Tapovan-Vishnugad hydropower project in Uttarakhand after a 2021 glacier burst is often cited as a reminder that Himalayan infrastructure needs to be designed with real climate resilience in mind, not just structural engineering. The same unpredictability that makes a regulating reservoir attractive to planners is the unpredictability that Adi communities have spent generations learning to read. A resettlement and planning process that treats this knowledge as incidental – rather than something worth documenting, consulting and, where possible, integrating into the project’s own risk assessments – would be missing a resource that is genuinely useful, not just symbolically important.
Finding the balance
None of these points toward an easy answer, and it shouldn’t. India’s interest in building water-regulation capacity on its own side of an unregulated, treaty-less river is reasonable, and the Northeast’s power needs are real. Equally, a project on this scale, in a seismically active and ecologically rich valley, inhabited by communities with a deep and specific relationship to the land, deserves a process that treats consent as something to be earned rather than assumed, and treats displacement as a cost to be minimised and fairly compensated rather than a formality to be managed.
A more balanced path forward would combine several things that are not, in practice, in tension with one another: continuing to build India’s flow-regulation and storage capacity as a genuine safeguard; pursuing a diplomatic engagement with China and a consultation mechanisms, so that unilateral infrastructure is not the only tool available; ensuring that consent processes with Siang valley communities are transparent and free of ambiguity about what has actually been agreed; and formally documenting and drawing on Adi and Galo ecological knowledge as part of the project’s own climate-resilience planning, rather than treating it as something the reservoir will simply submerge.
Water security, humanitarian concerns and India’s strategic interests in the Northeast are not, ultimately, competing priorities. A project that succeeds on only one of these fronts – power and flood control without community trust, or vice versa – will not have solved the underlying problem the Siang valley faces. Getting SUMP right, and not merely getting it built, is what will determine whether it becomes a durable answer to the region’s water security question or another source of the very instability it is meant to guard against.
(The author is a Climate Adaptation, Resilience & Energy Transition Professional)
