The Arunachal Pradesh government has stepped up preparedness against possible Glacial Lake Outburst Floods (GLOFs) after scientists identified high-risk glacial lakes in the state and warned that rising temperatures are driving significant changes in the number and size of high-altitude lakes across the Eastern Himalayas.
The latest alert follows a scientific assessment of the Khangri Glacier region near the transboundary border with Tibet. The Tawang district administration, under the District Disaster Management Authority (DDMA), has issued a high-altitude public advisory urging residents, tourists, transport operators and security personnel to remain vigilant in vulnerable river basins.
The assessment was carried out during the 5th Khangri Glacier Expedition by the Centre for Earth Sciences and Himalayan Studies (CESHS), in collaboration with experts from the National Centre for Polar and Ocean Research (NCPOR) and the North Eastern Regional Institute of Science and Technology (NERIST).
Scientists identified a potentially unstable proglacial lake at an altitude of around 16,500 feet in the Mago Chu basin. They also observed an active “Glacier Sinking Zone”, where parts of the glacier’s snout are collapsing amid rising temperatures and climatic changes.
Researchers warned that accumulated meltwater and unstable moraine debris trapped behind fragile natural barriers could cause a sudden breach, sending a surge of water downstream into river systems connected to the Brahmaputra basin.
The district administration has advised people to avoid riverbanks along the Tawang Chu and Mago Chu basins, suspend non-essential movement on high-altitude routes during heavy rainfall and refrain from crossing flooded streams or weakened bridges. Tourists and commercial drivers have been asked to check weather conditions and road clearances before travelling through mountain corridors.
Residents have also been urged to report unusual signs such as sudden drops in river levels, muddy water surges and fresh ground fissures, which may indicate upstream blockages or glacial instability.
The concerns are reinforced by a new study published in Discover Hazards, which assessed 127 high-altitude and glacial lakes in Arunachal Pradesh using satellite data from 1988 to 2020. Researchers from Cotton University and Nagaland University — Nabajit Hazarika, Vimha Ritse, Amenuo Susan Kulnu and Latonglila Jamir — used the Analytic Hierarchy Process to evaluate GLOF risks based on factors including lake expansion and proximity to glaciers.
The study classified 89 lakes as low risk, 36 as medium risk and two as high risk. The medium- and high-risk lakes are concentrated mainly in Upper Dibang Valley, West Kameng and Tawang, areas that contain downstream settlements as well as important hydropower infrastructure.
The research also found major changes in the lake landscape over the past three decades. Non-glacial lakes increased by 498, with their combined area expanding by more than 3,200 hectares. Unconnected glacial lakes increased from 136 in 1988 to 205 in 2020. Proglacial lakes showed a decline in number but an increase in total area, from about 110.7 hectares to nearly 126 hectares.
Most newly formed lakes were concentrated at elevations between 4,000 and 5,000 metres, an altitude range where glacier retreat is particularly active.
A GLOF occurs when water stored in a glacial or high-altitude lake is suddenly released, often after the failure of a natural moraine, ice or rock dam. Such floods can carry huge volumes of water, rock and sediment downstream, damaging settlements, roads, bridges and hydropower facilities.
Researchers warned that the risk could increase as glaciers retreat and lakes expand under global warming. Since many rivers originating in Arunachal’s high-altitude basins eventually feed the Brahmaputra system, a major GLOF could affect areas far beyond the immediate mountain valleys, including downstream parts of Assam.
Separate satellite-based monitoring has also raised concerns. An assessment by Suhora Technologies found that four of five glacial lakes classified as high-risk by the National Disaster Management Authority (NDMA) in the Mago Chu basin had expanded between 2016 and 2026. Sanhapo, or Sangacho, Lake showed particularly significant growth.
The state has intensified preparedness following the devastating South Lhonak Lake GLOF in Sikkim in October 2023. The Arunachal Pradesh State Disaster Management Authority (APSDMA) has conducted specialised training using bathymetry equipment to assess lake depth and water volume. Teams from the India Meteorological Department (IMD) and Geological Survey of India (GSI) are also expected to undertake detailed field mapping of vulnerable lakes.
Under the National GLOF Risk Mitigation Project, authorities are preparing to install automated water-level recorders, satellite-linked early-warning sirens and high-altitude weather monitoring systems. Expert teams have also been deployed to high-risk lakes for detailed field studies, including mapping lake boundaries, accessibility, elevation, nearby settlements and geographical coordinates.
Union Home Secretary Govind Mohan recently reviewed GLOF and avalanche preparedness with Arunachal Pradesh and other Himalayan states and Union Territories. He stressed continuous monitoring of vulnerable lakes and avalanche-prone areas, faster warning systems and effective evacuation planning.
District administrations, Village Disaster Management Authorities and emergency response teams have been placed on round-the-clock alert to coordinate evacuation measures if abnormal water surges are detected.
Scientists have acknowledged limitations in the risk-screening method used in the Discover Hazards study but said it remains useful in data-scarce regions such as Arunachal Pradesh, where detailed monitoring of remote high-altitude lakes is difficult.
The combined findings point to a growing climate-related hazard in the Eastern Himalayas. Scientists and disaster-management authorities have called for sustained monitoring, detailed risk mapping and stronger early-warning systems to protect vulnerable mountain communities as well as the much larger downstream population dependent on rivers originating in Arunachal Pradesh.
