IIT Mandi maps 2,076 glacial lakes in Himachal, flags nine as risky

What happened

The study was led by Professor Dericks P. Shukla, founding chairperson of the School of Civil and Environmental Engineering at the Indian Institute of Technology (IIT) Mandi, with a six-member team. According to the Press Trust of India (PTI) report, carried by Telangana Today and Kashmir Reader, the team used satellite images and other data to compare glacial lakes in Himachal Pradesh in 2015 and 2025.

They counted 2,076 glacial lakes above 3,500 metres in 2025, around 710 more than in 2015. The combined area of the lakes grew by 28.45 percent over the decade. The researchers say the number of glacial lakes in the wider Himalayan region has risen by nearly 30 percent in the past ten years. The report was published days after deadly floods in Nepal, which the researchers mentioned as a warning.

Nine lakes were named as especially vulnerable: Kalikund, Chandratal, Vasuki, Surai, Kya Tso, Yoche, Samudra Tapu, Kasang and Gepang Gath, in high areas including Chamba and Lahaul-Spiti. Gepang Gath grew by about 244,000 square metres, Kasang by nearly 150,000 and Kalikund by about 120,000. Kalikund was flagged as especially sensitive because of the steep slopes around it, which could lead to a sudden collapse or outburst.

The study warns that more than 15 bridges, several settlements, and schools and health facilities lie in the possible flood paths of these lakes. India's Central Water Commission and National Disaster Management Authority currently list four lakes in Himachal Pradesh as sensitive, and three of them are in the IIT Mandi list. The state government has asked the central government for 105 crore rupees for early warning systems and other measures at four major lakes.

The engineering behind it

Mapping glacial lakes from space is now a standard method. In general, water absorbs most near-infrared light, while snow, ice and rock reflect it, so lakes stand out clearly in multispectral satellite images. Researchers often calculate a water index from two image bands to separate water from land automatically. The outlines are then checked by eye, because shadows, frozen surfaces and debris on glaciers can confuse the software.

Once lakes are mapped for two dates, they can be compared in a geographic information system (GIS). This shows which lakes are new, which have grown and by how much. Growth alone does not make a lake dangerous. Engineers also look at what holds the water back, how steep the surrounding slopes are, whether ice or rock could fall into the lake, and what lies downstream.

The IIT Mandi team pointed to several triggers. A landslide, earthquake or other ground movement could cause a sudden drainage event. The researchers also said that more tourist activity in sensitive areas can increase dust on glaciers. Dust absorbs more sunlight than clean snow and ice, which speeds up melting. They stressed that satellite tracking must be combined with field monitoring, early warning systems and stronger government action.

What happens next in India

Officials told PTI that the Central Water Commission will carry out flow-path analysis and downstream risk assessment for 681 glacial lakes across the Himalayan region. Flow-path analysis traces the route a flood would take from a lake down the valley, and shows which villages, roads and bridges lie in its way. The National Disaster Management Authority will develop a combined framework to place lakes into risk categories.

This step is where civil engineering enters directly. Once a flood path is known, engineers can estimate how much water could arrive, how fast and how deep. That information decides where warning sirens should go, which bridges need checking, and whether protective works or lake-lowering are needed. It is also where mistakes are costly. A flood path traced on a poor terrain model can miss a village or wrongly include one, so the elevation data, the assumed flood volume and the channel shapes all need careful checking against field visits.

What it means in Nepal

Nepal faces the same hazard. Nepalnews reported that a flood on 26 August 2026 swept down the Bhote Koshi and Trishuli rivers, and that 903 people had died by 31 August. Early assessments linked it to a large glacier collapse upstream in Tibet. Nepalnews also reports that a joint assessment by ICIMOD, the International Centre for Integrated Mountain Development, and the government lists 47 potentially dangerous glacial lakes, 21 of them inside Nepal.

According to the same report, broader inventories put the total number of glacial lakes in Nepal at between about 2,070 and 3,000, depending on the survey year and method. That range is itself a sign that lake inventories need regular updating with consistent methods. The approach used at IIT Mandi, comparing free satellite images over time in GIS, is one that can be learned with ordinary computers and publicly available data.

For students, this is a realistic area for a final-year project. Mapping lakes in one river basin over several years, then tracing possible flood paths toward bridges, roads or hydropower intakes, combines remote sensing, hydrology and hydraulics. Field data and expert review would still be needed before anyone used such results for real decisions.