Nepal’s Rasuwa Flash Flood on Nepal-Tibet Border

A catastrophic high-altitude flash flood strikes Nepal’s Rasuwa district along the Nepal-Tibet border, with floodwaters originating from upstream in Tibet and moving through the Lhende Khola, Bhote Koshi, and Trishuli River corridors. ICIMOD assessments indicate that a high-altitude ice and rock avalanche in Tibet collapses into the Lhende Khola, temporarily impounding water that breaches rapidly and releases a high-velocity surge downstream.

Nepal Rasuwa Flash Flood:

Dimension	Key Details
Immediate physical mechanism	Avalanche debris temporarily impounds water in a narrow valley section, and the natural barrier breaches rapidly, releasing a massive, high-velocity surge of water, sediment, and boulders downstream.
Triggering events	Extreme events are triggered by thermal and structural instabilities in frozen water environments, including Glacier Lake Outburst Floods (GLOFs), permafrost degradation, and high-altitude ice-rock avalanches.
Cascading disaster phenomenon	The cascading disaster phenomenon occurs when a primary cryospheric trigger, such as an avalanche, creates secondary hazards, such as landslide dam impoundment, leading to tertiary impacts, including catastrophic downstream flooding and infrastructure failure.
Hydropower and transmission assets damaged	The flood damages at least 6 major hydropower and transmission assets, including the 111 MW Rasuwagadhi, 78 MW Sanjen Khola, and 60 MW Upper Trishuli 3A projects.
Power capacity disrupted	The damage disrupts nearly 430 MW, around 12% of Nepal's total installed power capacity.
Trade and connectivity impact	The flood severely damages the Rasuwagadhi-Gyirong customs checkpoint and key bridges, halts Nepal-China overland trade, and prompts heightened flood alerts along the lower Narayani (Gandak) and Koshi river basins in northern India.
Lhende Khola	Lhende Khola is a high-altitude transboundary stream on the Nepal-Tibet border where the avalanche impoundment occurs, and it is a key tributary of the Bhote Koshi.
Bhote Koshi River	Bhote Koshi is a transboundary river originating in the Tibetan Plateau and acts as the main upper conduit for the flood surge.
Trishuli River	Trishuli River is formed by the confluence of Bhote Koshi and Langtang Khola at Syabrubesi, and it is one of the main tributaries of the Narayani (Gandak) system.
Narayani/Gandak River	Narayani/Gandak is a major transboundary river system carrying meltwater from central Nepal into the Gangetic plains of Bihar, India.
Rasuwa District	Rasuwa District is a mountainous border district in Bagmati Province, central Nepal, and is home to the Langtang National Park corridor.