Guwahati | Arunachal Pradesh has 197 expanding glacial lakes, including 32 classified as high-risk and requiring active mitigation, raising concerns over possible glacial lake outburst floods (GLOFs) in downstream river systems, internationally acclaimed river expert Prof Nayan Sarma has said.

Speaking to The Assam Tribune, Sarma said Arunachal Pradesh and Bhutan, located in the highly vulnerable Eastern Himalayas, were witnessing rapid glacier melt and the formation and expansion of unstable proglacial lakes.

Several major river systems are potentially exposed to GLOF risks, including the Tawang Chu and Dibang in Arunachal Pradesh and the Punatsang Chhu and Kuri Chu in Bhutan. The Kameng Chu, also known as the Mago Chu in its upper reaches and the Jia Bharali in Assam, is particularly vulnerable to GLOF events originating from the rapidly melting Khangri glacier in Tawang district.

Scientists have identified unstable proglacial lakes at an altitude of around 16,500 feet near the Khangri glacier. High-risk lakes in the Mago Chu basin have expanded significantly over the past decade, with the National Disaster Management Authority (NDMA) identifying them as potentially dangerous.

Sarma said a 2026 satellite analysis showed that the high-altitude Sanhapo Glacial Lake in the Mago Chu basin had expanded from 56 hectares in 2016 to 89 hectares, heightening concerns over a possible GLOF. The threat extends beyond Arunachal Pradesh into Bhutan and Assam. The Punatsang Chhu basin has previously witnessed major outburst events, including the 1994 Lugge Tsho disaster, while Thorthormi Tsho remains among the high-hazard glacial lakes in Bhutan.

The Punatsang Chhu, which has two hydropower projects, is known as the Sankosh in Assam.

Glaciers in northern Bhutan feed seven major river systems – the Amo Chu, Wang Chu, Punatsang Chhu, Mangde Chu, Chamkhar Chu, Kuri Chu and Drangme Chu. Hydropower generated from these river systems contributes significantly to Bhutan’s economy, with much of the electricity exported to India.

Sarma said the interconnected nature of the river systems meant that a major GLOF in the upper reaches could have consequences far downstream.

The Kuri Chu and Drangme Chu from Bhutan, along with the Tawang Chu from Arunachal Pradesh, eventually join the Manas river system in Assam. Any major GLOF propagating through these high-altitude rivers could therefore pose a significant threat to downstream areas in Assam.

He stressed the need for an integrated system combining real-time satellite monitoring, field-based sensors and structural engineering measures to assess and mitigate GLOF risks. High-resolution satellite imagery and Interferometric Synthetic Aperture Radar (InSAR) should be used to monitor changes in glacial lakes and detect potential instability in moraine dams, he said.

Synthetic Aperture Radar (SAR) is particularly useful because it can monitor glacial deformation through cloud cover and darkness, allowing observations even during storms and prolonged winter conditions. Sarma also suggested deploying solar-powered Automated Weather Stations near high-risk lakes to continuously monitor temperature changes, weather conditions and fluctuations in water levels.

With glacial lakes expanding across the Eastern Himalayas, he said sustained monitoring and advance mitigation would be crucial to protect downstream communities, infrastructure and river systems in Arunachal Pradesh, Bhutan and Assam.