At least 300,000 people in parts of the Himalayan region could now be living in the path of potential disasters, according to a new peer-reviewed study. The research found that built-up land in high-risk zones in northern Nepal, parts of south-eastern Tibet and a corner of India's Uttarakhand grew by about 45% between 2016 and 2023. In areas most threatened by flooding from glacial lakes, development rose by almost 78% over the same period.

The study was published in Scientific Reports and covered by the BBC's environment correspondent Navin Singh Khadka. Its central finding is a pairing: a construction boom in mountain valleys, and a growing share of that construction sitting where floods, landslides and glacial lake outbursts can reach it.

What the study actually measured

Nine researchers from the UK, Nepal and India looked at land up to 50km (30 miles) downstream from Himalayan rivers, and around 1,360 glacial lakes. They classified buildings as at risk if they stood within 50 vertical metres (164ft) of a river or a glacial lake's surface.

That definition matters for reading the 300,000 figure. It is an estimate of people in the analysed territory, not a count of everyone in the Himalaya. The authors say the true number under threat could be much higher, because they only studied a specific area and not neighbouring regions facing similar risks.

The growth includes tourism facilities, infrastructure and real estate, visible in Pokhara, a tourist hub that has expanded over three decades to serve a surge in visitors.

Why the exposure is rising

The region's hazards are largely driven by warming that scientists say is happening at twice the global rate. That has sped up the melting of glaciers, icefields, snowpacks and ground that is normally frozen all year.

Melting destabilises slopes that earthquakes also shake, fills glacial lakes until they burst (Nepal has documented around 30 such events since 1940), and brings rain to altitudes that used to see only snow, triggering rock and ice falls.

Buildings have moved into those paths quickly. The BBC visited Pokhara, where Mayor Dhana Raj Acharya says dealing with the risk from the Seti Gandaki river, which flows through the city from the Annapurna range, is a huge challenge. Many old buildings stand just 5m (16ft) from the river banks, he says, despite new rules requiring them to be further back. "Where we move them, and how we do that, is the real challenge."

North of the city, the Annapurna trekking region has seen a major increase in settlements along river banks, some hit by recent floods and landslides. Phurpa Chhiring Lama, who runs a homestay there, says normally all 20 of his rooms are occupied in peak trekking season. Now five are. "We have been doing this business for more than 40 years, but we've never seen this kind of disaster."

Krishna Gauchan, whose hotel is close to the glacier-fed Modi river, describes living in constant fear. "This river can flood if the glacier collapses or if the glacial lake bursts out," he says.

The planning gap

Khagendra Poudel, a geographer at a local campus of Tribhuvan University, suggests tourism investors promote some of these spots as destinations without factoring in the risks. Laxman Subedi, president of the Hotel Association Pokhara, says businesses expanded without proper planning. "By the time disasters hit, it is too late," he says.

Tourism is not the only driver. The areas around the Bhotekoshi and Trishuli rivers have seen a significant rise in hydropower construction.

The study's lead author, University of Leeds glaciologist C Scott Watson, draws the planning conclusion directly. "As river valleys become increasingly populated, development decisions being made today will shape disaster risk for decades to come," he says.

The risk envelope may also be wider than the study's threshold. During catastrophic flooding on 26 August, locals in Rasuwa district said the river rose by 70m (230ft) at some points, so buildings relatively far from the banks were hit and buried by debris.

What has already happened

The study was carried out before the mass floods in August which left more than 1,400 people dead and thousands missing in Nepal. Since then there have been smaller incidents, including flooding along the Budhi Gandaki river on 11 October that damaged 200 houses, swept away five bridges and left five people missing.

Authorities are responding on paper. Nepal's disaster agency says settlements within 15m (49ft) of the riverbank along the devastated Rasuwa-Bhotekoshi corridor will soon be banned. Its chief executive, Dharam Raj Uprety, says enforcement is hard because people are attached to their land, "but we cannot ignore the increasing risks".

Uttarakhand approved new floodplain zoning rules on 12 October, saying the aim is to protect life and property while maintaining the flow of flood water. Activist Anoop Nautiyal says zoning rules exist on paper with no implementation on the ground.

Urban planner Surya Raj Acharya points to the same pattern: roads, hotels and market towns expanded on the low, flat land along rivers because it is buildable, while safeguards such as keeping off the river bank were ignored. "A fragile ecosystem like the Himalaya demands stricter planning than elsewhere, yet these rules have been weak and poorly enforced," he says.

What the numbers can and cannot show

The 45% and 78% growth figures describe built-up land in the studied zones, not the number of people or the value of the property. The 300,000 is the population estimate attached to that exposure, and the authors say it is conservative because of the territory they covered.

The study does not claim climate change alone explains any single disaster; it maps where development has grown relative to hazards that warming is intensifying.

Rules on riverbank setbacks and floodplain zoning exist in both countries. The gap the BBC documents is between those rules and construction on the ground.

Basanta Raj Adhikari, director of the Centre for Disaster Studies at Tribhuvan University, doubts the threat can be mitigated completely. He suggests insurance grades as another lever: if authorities mapped high, moderate and low risk, coverage would follow, and people who build in safer places would get better protection.

Alton Byers, a mountain geographer at the University of Colorado who was not involved in the study, says it should serve as a "springboard" for more effective early-warning systems and other precautions. The building is not stopping, so the useful work is in where it goes and what warning people get when the water rises.