Nepal disaster exposes gaps in Himalayan hazard assessment and planning

The devastating flash floods in Nepal have highlighted the need for systematic scientific assessments of glacial lakes, stronger early-warning systems and clear land-use policies across the Himalayan region, experts have said.

At least 270 people have been killed, and thousands remain missing, including 288 Indian tourists, after flash floods struck several parts of Nepal on Wednesday. The disaster swept through towns and villages, destroyed critical bridges and disrupted about a dozen hydropower projects.

Researchers at the Kathmandu-based International Centre for Integrated Mountain Development are examining whether an ice-rock avalanche at a high-altitude location triggered the flooding.

Their preliminary assessment, based on videos and information from affected areas, suggests that a large quantity of ice and rock debris may have fallen into the Lende Khola, a tributary of the Bhote Koshi River. The impact could have produced a sudden surge of water, sediment and large boulders downstream.

Mohd Farooq Azam, senior cryosphere specialist at ICIMOD and associate professor at the Indian Institute of Technology Indore, said the event could be linked to the changes occurring across the Himalayan landscape because of global warming.

“It is related to climate change because the snow covers are reducing, the glaciers are receding, more rocky or barren areas are exposed — they absorb more heat which makes the slopes more vulnerable,” Azam told PTI.

Although scientists have yet to establish the exact cause, he said reduced snow cover, retreating glaciers and degradation of permafrost may have contributed to slope instability.

Research has shown that extreme precipitation in the Himalayas, including episodes of heavy snowfall, increases snow accumulation only temporarily. A study published in Global and Planetary Change found that such events do not reverse the broader decline in snow cover.

Another study, published in the Journal of Hydrology: Regional Studies, found that the number of glacial lakes in Himachal Pradesh increased by 525 per cent between 1990 and 2024, while their combined area doubled. The number of smaller lakes rose from nine to 487 during this period.

Reet Kamal Tiwari, associate professor and head of the Department of Civil Engineering at IIT Ropar, said glacial lakes could form through several processes and be contained by moraines, glacier ice, bedrock depressions or other geological formations.

However, he cautioned that the existence of a glacial lake did not automatically mean it posed an immediate danger to nearby communities.

Scientists must first assess the lake’s stability, its vulnerability and the external factors that could cause a sudden discharge, Tiwari said.

“The concern is not simply the increasing number of glacial lakes; it is the combination of increasing hazard potential and increasing downstream exposure,” he added.

Landslides, intense rainfall, snow or ice avalanches, rockfalls and the collapse of hanging glaciers can all trigger the sudden release of water from a glacial lake.

Experts also pointed to limitations in warning systems that are designed mainly around rainfall. Soniya Rijal, a postdoctoral research associate at the University of Sydney, said the absence of heavy rain may have led people to underestimate warnings issued by residents in the affected valleys.

“What this event shows is that our warning systems, formal and informal, are built around rain,” she said.

Rijal said some residents had reportedly alerted their neighbours before the floodwaters arrived, but many did not take the warnings seriously because the region had not received heavy rainfall.

The Nepal disaster bears similarities to the February 2021 floods in Chamoli district of Uttarakhand. In that incident, a massive ice-and-rock avalanche from Ronti Peak triggered a sudden surge through the Rishi Ganga, Dhauliganga and Alaknanda rivers. Hydropower facilities were severely damaged, while about 300 people, most of them workers at dam sites, were reported killed or missing.

Azam, however, cautioned against applying the same explanation or solution to every Himalayan disaster.

“Every disaster is unique. First, we need to understand the processes and then we need to design some mitigation measures accordingly,” he said.

Tiwari called for scientific assessments of potentially dangerous glacial lakes and the areas lying downstream. Such studies should examine the lake, the structure containing it, the surrounding terrain, possible triggers, likely flood paths, and the settlements and infrastructure that could be affected.

He said these assessments should bring together specialists in glaciology, geomorphology, hydrology, remote sensing, geotechnical engineering and disaster management.

Experts also urged authorities to regulate construction and settlement patterns in vulnerable river corridors.

“The problem is we are settling very close to the river and sometimes on the river. The urgency is to develop a land use policy,” Azam said.

He called for better planning of settlements and infrastructure, warning that the frequency and intensity of extreme events had increased over the past two decades.

Azam also said conventional environmental impact assessments were no longer sufficient. While infrastructure projects are routinely assessed for their impact on the environment, planners must now examine how a rapidly changing environment could affect those projects.

Such assessments should evaluate how settlements, bridges, roads, dams and hydropower facilities would withstand cloudbursts, intense rainfall, glacial lake outburst floods, avalanches and other cascading hazards, he said.

With PTI inputs