Population at risk of Himalayan floods estimated

Nearly 300,000 people may live in areas at risk of flooding in the Nepalese, Indian, and Chinese areas of the Himalayas. The results, from a study published in Scientific Reports, also indicate that the total area covered by buildings within potential flood zones increased by approximately 45% between 2016 and 2023.

Flooding in the Himalayas is typically caused by seasonal monsoons, extreme rainfall, or rare but devastating debris flows or floods from glacial lakes (known as glacial lake outburst floods). Climate change is predicted to increase the severity of these events, while the steep, narrow valleys in mountainous areas can exacerbate flood heights and the subsequent effects. However, the number of people at risk from flooding in this area remains unclear.

C. Scott Watson and colleagues assessed changes in the potential exposure of buildings and people to flooding between 2016 and 2023 in areas up to 50 km downstream of 1,361 Himalayan lakes in Nepal and neighbouring regions of India and China. They used five datasets validated against manually recorded data to estimate the total building footprint (the area covered by the bases of all existing buildings) in these areas. The estimated footprint of buildings within 50 vertical metres of a river channel — used as a proxy for exposure to potential flooding — increased by 45.75%, from 12.38 to 18.04 km². In areas at a high risk of glacial lake outburst floods, the footprint increased by 77.78%, from 0.72 to 1.28 km².

The authors then used the calculated building footprint to estimate that, in 2026, approximately 293,800 people (18% of the population in the study area) may live in buildings exposed to potential flooding. This includes an estimated 108,500 people in Nepal, of whom 22,800 live within 10 vertical metres of a river channel. The population living within the flood risk zones is projected to increase by 17,900 (6%) between 2015 and 2030.

The authors caution that the estimates of both total building footprint and population growth are highly uncertain. They highlight the need for more accurate building databases to better calculate risk.

Article details: Increasing exposure to potential flooding in high-mountain catchments

DOI: 10.1038/s41598-026-70268-0

Corresponding Author: 

C. Scott Watson
University of Leeds, Leeds, UK
Email: [email protected]

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