KATHMANDU: The Department of Hydrology and Meteorology (DHM) has attributed the recent flash flood in the Lhende River, on the Nepal-China border in Rasuwa, to a glacial lake outburst in its preliminary study. The study, based on Sentinel satellite images, indicates that water breached from a “supraglacial” lake formed on top of a glacier.
According to Binod Parajuli, Chief of the Flood Forecasting Division under DHM, the lake is situated around 36 km north of Rasuwagadhi on the Nepal-China border, within the upper catchment area of the Lhende River. Its coordinates are Latitude: 28.4043, Longitude: 85.6469, at an altitude of about 5,150 meters above sea level.
Releasing a special bulletin on Thursday, DHM said, prior to the flood, the supraglacial lake measured around 0.75 square kilometers. Post-flood images, however, show its size reduced to roughly 0.60 square kilometers. This reduction suggests a significant discharge of water from the lake, impacting downstream areas, it said.
The DHM’s analysis of Normalized Difference Water Index (NDWI) images from July 5, 2025 (before the flood) and July 8, 2025 (after the flood) clearly showed a change in the lake’s surface and significant alterations in the downstream region.
Similarly, Normalized Difference Vegetation Index (NDVI) images from the same dates also reveal considerable differences between pre- and post-flood conditions, further confirming the water release from the lake. Most importantly, the shrinkage of the glacial lake’s area confirmed that water was released from the lake, triggering the flood, the DHM said.
The department expects further on-site reports from China and anticipates that additional satellite imagery will provide more confirmation of these findings. The DHM will continue its ongoing study and provide updates, Parajuli said. Separately, scientists from the International Centre for Integrated Mountain Development (ICIMOD) have also confirmed that the Bhotekoshi River flood in Rasuwa was caused by a glacial lake outburst from the Lhende River, near the Nepal-China border.
