Nearly 300,000 at risk from Himalayan floods, as flood zone building accelerates

Nearly 300,000 people in Nepal, India, and China may be at risk of flooding in the Himalayas, according to a recent study. The findings, published in Scientific Reports, reveal that the number of buildings within potential flood zones has surged by nearly 45% between 2016 and 2023. This increase in buildings near rivers and glacial lakes, which can cause devastating floods, has led researchers to estimate that about 293,800 people may reside in areas exposed to potential flooding by 2026.

Flooding in the Himalayas is primarily caused by monsoons, heavy rainfall, or sudden glacial lake outburst floods. As climate change intensifies these events, flood heights and effects become more severe, especially in steep and narrow valleys. However, the exact number of people at risk remains unclear due to the uncertainty in building and population estimates.

Using five validated datasets, researchers calculated the total building footprint within 50 vertical meters of river channels, which serves as a proxy for flood exposure. They found that this footprint increased by 45.75% overall and 77.78% in high-risk zones due to glacial lake outburst floods. In areas facing such risks, the building footprint rose from 0.72 to 1.28 km2 (0.28 to 0.49 square miles).

By 2026, the study projects that around 293,800 people (18% of the population in the study area) may live in buildings exposed to potential flooding. Specifically, 108,500 people in Nepal, with 22,800 residing within 10 vertical meters of a river channel, could be at risk. Additionally, the population living within flood risk zones is expected to grow by 6% between 2015 and 2030.

While the estimates of building footprint and population growth are highly uncertain, the study emphasizes the urgent need for more accurate building databases to better calculate flood risks in the Himalayas.