KATHMANDU, Sept 3: Glacial lake outburst floods and avalanches are not new phenomena in Nepal. As a Himalayan country, Nepal has naturally experienced occasional glacial lake outbursts.
Experts, however, say climate change over the past three decades has increased both the frequency and scale of such disasters. Events that once occurred at intervals of 20 to 60 years are now occurring almost every year.
The National Assembly’s Development, Economic Affairs and Good Governance Committee has taken serious note of the growing frequency and volume of floods. Committee secretary Dr Rojanath Pandey said preparations were underway to draw the government’s attention to taking the issue of climate compensation to international forums.
On the morning of Bhadra 10, an avalanche or ice rock fall in the Lhende River area, northeast of Rasuwagadhi in China’s Tibet Autonomous Region, triggered a flood that flowed through the Bhotekoshi and Trishuli rivers before reaching the Narayani. It caused extensive damage in Rasuwa, Nuwakot, Dhading, Gorkha, Tanahun and Chitwan, among other districts. According to the latest figures released by the National Disaster Risk Reduction and Management Authority and Nepal Police, the death toll continues to rise.
The number of dead and missing remains subject to change as authorities update their figures. The government has initially estimated physical damage at more than Rs 200 billion. The Nepal Army, Nepal Police, Armed Police Force and foreign rescue teams have been deployed for search and rescue operations. Efforts to rescue people trapped inside hydropower project tunnels are also continuing.
The disaster is being described as the deadliest Himalayan disaster recorded so far. Experts have referred to it as a “Himalayan tsunami”. Previous events generally caused far fewer casualties. This time, however, the flood reached the densely populated Tarai and Bhabar regions, significantly increasing the scale of the damage.
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Floods caused by massive flows of water from the mountains or by the collapse of glacial lakes or ice dams are known as glacial lake outburst floods, or GLOFs. More than 26 major such events have been recorded in Nepal. Fourteen originated within Nepal, while the others caused damage in Nepal after glacial lakes burst in Tibet, China.
Several major incidents illustrate the pattern. On Bhadra 32, 2081, a flood struck Thame in Solukhumbu after a landslide fell into a glacial lake above Thame in Khumbu Pasang Lhamu Rural Municipality 5, causing two interconnected lakes to burst. No one was killed, but around 13 to 17 houses were completely destroyed, a school and health clinic were swept away, and electricity generation stopped after the dam of the Khumbu Electricity Company was damaged.
In the Langmoche Valley of Solukhumbu, an avalanche falling into Dig Tsho Glacial Lake caused an outburst on Shrawan 20, 2042, when its natural dam collapsed. The incident destroyed the under-construction Namche Small Hydropower Project, several bridges and agricultural land, and killed three people.
On Bhadra 18, 2055, Tam Pokhari Glacial Lake in Sankhuwasabha burst, sweeping away several bridges and killing at least two people.
On Ashadh 27, 2038, Zhangzangbo Cho Lake in Tibet burst, sending floodwaters into the Bhotekoshi and Sunkoshi corridor. The Miteri Bridge, sections of the Arniko Highway and the dam of the Sunkoshi Hydropower Station were destroyed.
On Shrawan 19, 2034, the Imja and Nare glacial lakes in Solukhumbu burst, releasing around 400,000 cubic metres of water and causing extensive damage to infrastructure and livestock.
Rasuwa, Nuwakot, Solukhumbu, Sankhuwasabha and the Bhotekoshi corridor in Sindhupalchok are among the areas repeatedly exposed to such disasters. Hydropower projects, strategic bridges, schools, highways and hundreds of hectares of farmland remain at risk.
In Manang, three days of heavy rainfall beginning on Ashadh 1, 2078 triggered severe floods and landslides in the Marsyangdi River and local streams, causing extensive damage in Chame, Naso and Ngisyang rural municipalities. More than half of the settlement in the popular tourist area of Tal village was submerged. A Bailey bridge, numerous suspension bridges, roads and small hydropower plants were swept away, leaving Manang disconnected from the rest of the country for an extended period. More than 1,000 people were displaced.
During the second week of Shrawan 2042, a massive flood caused by a glacial lake outburst and landslide in the Kali Gandaki region, including Mustang and Dana in Myagdi, killed two people and displaced more than 32 families, according to official records. They were later resettled in Dhorphirdi, Tanahun. Hundreds of ropanis of farmland along the river were eroded and turned into riverbed.
Similar risk in neighbouring countries
Glacial lake outburst floods have also caused major destruction beyond Nepal. On the night of Ashwin 17, 2080, a mountain collapse into South Lhonak Lake in North Sikkim caused the lake to burst and triggered a massive flood in the Teesta River. The flood swept away the Teesta 3 dam, the largest hydropower project in Sikkim.
Scientific studies confirmed at least 55 deaths in Sikkim, while dozens remained missing for weeks, including Indian Army personnel. The flood also affected areas of West Bengal and Bangladesh.
On Kartik 3, 2078, floods and landslides triggered by heavy rainfall killed 47 people in India’s Uttarakhand. The Kumaon region was the worst affected, with 42 deaths linked to flood related incidents.
Why is risk increasing?
Experts say the Hindu Kush Himalayan region is experiencing the effects of global warming more intensely than the global average, accelerating glacier melt. As glaciers retreat, old glacial lakes are expanding and new ones are forming.
At the same time, rainfall patterns are becoming more erratic, with extreme rainfall occurring in some locations while nearby areas receive little or no rain.
More than 2,000 glacial lakes are located across Nepal’s Koshi, Gandaki and Karnali basins. Of these, 21 on the Nepal side and 25 on the Chinese side, 46 in total, have been classified as extremely high risk, effectively making them potential “time bombs”.
Nepal often struggles to receive timely warnings about dangerous glacial lakes on the Chinese side. Experts say this contributes to repeated damage along the Bhotekoshi Sunkoshi corridor. They have called for a joint monitoring system and real time data sharing mechanism between Nepal and China.
Experts also recommend lowering water levels in highly vulnerable lakes using technologies similar to those used at Tsho Rolpa and Imja Lake in Solukhumbu. Continuous monitoring through satellites and drones, strict land use policies to prevent permanent settlements and structures along riverbanks, and disaster preparedness training for local communities are also needed.
