Guwahati: Assam Pradesh Congress Committee (APCC) president and MP Gaurav Gogoi has urged the Centre not to take any irreversible decision on the Siang Upper Multipurpose Project (SUMP) in Arunachal Pradesh without consulting Assam and commissioning an independent assessment of its downstream impact.

Gogoi wrote to Union Jal Shakti Minister C.R. Patil on October 29, raising concerns over the project’s possible implications for Assam.

He sought clarification on whether the Government of Assam had been formally consulted on SUMP and called for disclosure of the project assessments and hydrological studies.

Gogoi also demanded an independent downstream impact assessment covering Assam, prior consultation with affected communities and experts, and real-time data sharing between Assam and Arunachal Pradesh to strengthen flood monitoring and early-warning systems.

In his letter, he said the Siang was integral to the Brahmaputra basin and sustained Assam’s agricultural economy, riverine ecosystems and livelihoods. Any major intervention in its flow, he said, required careful assessment of the risks to flood management, water security and downstream communities.

While acknowledging that SUMP was being positioned as a strategic response to China’s proposed mega-dam on the Yarlung Tsangpo, Gogoi said the concerns of downstream communities in Assam must receive equal consideration.

He cautioned that the project’s stated objectives of maintaining year-round flows and moderating floods could not be treated as guaranteed outcomes. He cited the region’s vulnerability to extreme rainfall, landslides and glacial lake outburst floods.

Gogoi recalled that Assam had raised concerns over mega-dam projects in Arunachal Pradesh in the past. In 2014, then Chief Minister Tarun Gogoi had called for formal consultation with Assam before major dam projects were taken up in the neighbouring state. In 2015, he withheld support for the proposed Middle Siang project until its benefits to local communities could be demonstrated, stressing the need for consultation and safeguards for Assam.

Referring to Assam’s experience with the Lower Subansiri Hydroelectric Project, the Congress MP cited longstanding concerns over sudden water releases, riverbank erosion, flooding and the impact on downstream livelihoods.

He also referred to a 2025 study that documented concerns among downstream communities over flooding, declining fisheries and agricultural losses. These experiences, he said, reinforced the need for independent assessments, transparent monitoring and the participation of affected communities.

Gogoi further cited the 2013 Cumulative Impact and Carrying Capacity Study of the Siang Sub-Basin Including Downstream Impacts.

The study had identified possible ecological and livelihood consequences of the earlier proposed Siang projects, including the impact of daily winter water releases on river islands such as Kobo Chapori in Assam.

The study did not assess SUMP in its present form, according to the press release. Gogoi, however, said its findings reinforced the need for a comprehensive assessment of the project’s downstream implications.

He said flood moderation, dam safety and downstream ecological protection must remain central to the project’s appraisal. India’s strategic interests, he added, could not come at the cost of the safety and livelihoods of downstream populations.

He urged the Centre to ensure a transparent process that gives affected communities a meaningful voice.