Nepal study estimates nearly 300,000 people live in areas potentially exposed to flooding
Researchers found that built-up area near river channels in Nepal’s Himalayan catchments grew 46% from 2016 to 2023. Their screening identifies exposure, not the chance of a flood at any given site.
A study described on October 8 estimates that 293,800 people in Nepal and Himalayan river catchments draining into the country live in areas screened as potentially exposed to flooding. The researchers also found a 46% increase in built-up area close to river channels between 2016 and 2023, showing how development has expanded in places where flood hazards warrant closer assessment.
The research, published in Scientific Reports and explained by co-authors C. Scott Watson and Milan Shrestha, examines where people and buildings are located relative to mountain waterways. The estimate represents 18% of the population in the catchments covered by the study in 2026. It is a measure of potential exposure, not a prediction that those people will experience a flood.
What the Nepal flood exposure study measured
The authors combined satellite-derived building data with a measure called height above nearest drainage, or HAND. It estimates how high a location sits above its nearest river channel. In a steep valley, two buildings a short distance apart can be at very different heights, making their potential exposure difficult to judge from a map of horizontal distance alone.
The Scientific Reports abstract says building area within 0–50 metres vertically of river channels increased by 46% from 2016 to 2023. It separately reports a 77% rise in building area within modelled glacial lake outburst flood extents. These are changes in the area of buildings falling within the study’s screening zones; they are not counts of buildings flooded or damaged.
Watson and Shrestha say more than 100,000 people in the study region live downstream of glacial lakes. Such lakes form in depressions left by retreating glaciers and can release floodwater suddenly if a barrier fails. Being downstream identifies a reason to investigate a location’s hazard and preparedness; the figure alone does not establish the likelihood or severity of flooding for any particular settlement.
Why development is concentrated in Himalayan valleys
The researchers describe valley floors as some of the few flat, accessible places to build roads and settlements in the Himalayas. River corridors also provide routes through the mountains. Trade and tourism can bring roads, tracks, lodges and hydropower projects; homes and services may follow. That geography helps explain why development can grow in places where floodwaters and debris may also travel.
The August 26 Bhotekoshi–Trishuli flood illustrates the consequences a mountain corridor can face. A rapid analysis by researchers linked to Integrated Research on Disaster Risk says an ice, rock and soil mass failure appears to have blocked a river temporarily before the barrier breached. The report attributes damage to settlements, roads, more than 30 bridges, communications, and hydropower and transmission infrastructure along the corridor.
That rapid analysis relied on secondary information available online, and its account of the flood’s trigger remains the report’s reconstruction. The October exposure study asks a different question: how many people and how much development are located in places that merit flood assessment. Its population estimate is not a casualty figure for the August disaster.
What the screening can and cannot show
The authors present HAND as a way to identify places for closer investigation, particularly where steep terrain and limited detailed topographic data complicate flood modelling. It cannot replace detailed flood-hazard maps. A height band around a river does not show when water might arrive, how far it would spread in a particular event, or which individual buildings would be affected.
Exposure is also only part of disaster risk. The study’s authors point to building type, early warning, preparedness and evacuation planning as factors that shape the consequences of a flood. They say their findings do not imply that flooding is inevitable throughout the screened areas or that every project near a river should stop.
The researchers propose using exposure information in land and infrastructure planning to help limit future risk. Whether planners adopt this screening, commission more detailed local maps or change decisions as a result is not established by the study. For residents, its immediate value is a clearer account of where people and development overlap with potential hazards, and where more precise assessment is needed.
Sources and context
- Almost 300,000 people now live in flood-prone areas in the Nepalese Himalayas—new researchPhys.org / The Conversation
- Increasing exposure to potential flooding in high-mountain catchmentsScientific Reports
- Rapid analysis report: Scientific anatomy of the 26 August 2026 Bhotekoshi flash floodPreventionWeb (report by IRDR young scientists with IRDR ICoE IHRR and IRDR ICoE NSET)
AI-assisted article checked against the listed sources. NewsJaws did not conduct interviews or attend the reported events.
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