Impact of Climate Change on Glacial Lakes in the Himalayas: Rising Risks and Urgent Adaptation Measures

This story by Sonia Awale was originally published in Nepali Times. We’re sharing a condensed and edited version as part of a content-sharing agreement with Global Voices.

At 9:00 a.m. on August 16, a 4.5-magnitude earthquake shook Xizang on the Tibetan Plateau. Four hours later, a glacial lake in Nepal, 65 km away, burst, releasing a massive flood.

It’s unclear if the earthquake caused the lake’s outburst. It could have been triggered by an avalanche from Mount Tengi Ragi Tau’s southern ridge or by heavy monsoon rains causing a moraine collapse. Either way, the meltwater flowed into another lake downstream, setting off a destructive debris flow that swept through the valley, reaching as far as the village of Thame. Thankfully, the villagers had time to evacuate, and no lives were lost.

Thame experienced a more devastating flood on August 4, 1985, when a larger glacial lake in the nearby Dig Tsho valley burst after an avalanche. That flood claimed 12 lives, wiped out a newly built hydropower plant, and damaged a section of the road leading to Everest.

Tenzing Chogyal Sherpa, a glaciologist from the International Centre for Integrated Mountain Development (ICIMOD), recalls how his family’s home in Namche Bazaar was spared during the 1985 flood because it was built on high ground. But with roads destroyed, food supplies ran low, and his family survived on rotten potatoes.

Sherpa notes that the recent Thame flood serves as a warning about the dangers of living in the mountains, which are heightened by climate change. The region is surrounded by potentially dangerous glacial lakes, including Lumding Tso, Tso Rolpa, and Dig Tsho, all of which pose significant threats to downstream communities.

Although the Thame flood was smaller than the 2021 disaster that damaged the Melamchi reservoir or the 2023 Sikkim flood, the frequency of such incidents is increasing due to glacial lake outbursts and moraine collapses caused by heavy rainfall.

Anil Pokhrel, from the National Disaster Risk Reduction and Management Authority (NDRRMA), visited Thame on August 17 to inspect the glaciers above the village. He confirmed that two glacial lakes near Tashi Lapcha were responsible for the flooding. Satellite data showed that just two years ago, there were only four lakes, but hundreds of new glacial lakes have now formed across the Himalayas, many without names.

Some of the most dangerous lakes, like Tso Rolpa and Imja Tso, continue to expand rapidly. While larger lakes are known hazards, even small lakes can cause significant damage, as seen with the 1977 overflow of Lake Nare, which wreaked havoc on the region.

Even moderate flooding can be destructive, as the recent debris flow washed away a bridge over the Dudh Kosi River, worth 80 million rupees. Fortunately, most of the riverside villages had been evacuated, preventing casualties. A larger flood would have jeopardized major hydropower projects downstream.

Pokhrel observed unusually warm conditions during his visit to Thame, resembling the climate in Kathmandu. He also noted that satellite images had shown accelerated snowmelt in the region over the previous month, possibly leading to the cascading failure of the two lakes.

Glacial lake outbursts and debris flows are expected to become more frequent and severe in Nepal as climate change intensifies. The inherent seismic risks in the Himalayas further complicate the situation, making life in the region increasingly hazardous.

Local communities and governments must adapt by installing early warning systems, building smaller and decentralized hydropower plants, relocating infrastructure to higher ground, and carefully assessing risks.

Sherpa stresses the need for on-site observations, in addition to satellite tracking, in such a diverse and complex region. Despite the lack of ground-based data, advancements in remote sensing technology have helped fill the gaps and improve our understanding of the rapidly changing glaciers.

A report by ICIMOD highlights that glacier mass loss has surged by 65% in recent decades, with flood risks expected to rise even further in the coming century.

Given that many of Nepal’s rivers are transboundary, Sherpa emphasizes the need for an early warning system with China. To address the growing risks, Nepal also requires international assistance for adaptation and recovery.

Sherpa co-founded #SaveOurSnow, a global awareness campaign aimed at empowering Himalayan communities to combat climate-related risks. Through the campaign, Sherpa hopes to draw international attention to extreme weather events like monsoons, drying springs, winter droughts, and heatwaves, helping communities adapt and survive.