Rasuwa Bhotekoshi Flood 2026: Reconstruction of the Event and Rapid Damage and Needs Assessment

Abstract

On 26 August 2026, a rock-ice avalanche in the upper Bhotekoshi watershed near the Nepal–China border triggered a devastating debris flow that travelled over 180 km along the Bhotekoshi–Trishuli river corridor, reaching Devghat within six and a half hours. This study reconstructs the event using satellite imagery, seismic records, hydrological data, drone surveys and field observations. The findings identify a rock-ice avalanche as the primary trigger, ruling out earlier assumptions of a glacial lake or landslide dam outburst. Flood heights reached approximately 32 m at Betrawati and 12 m at Darshantar, causing extensive sediment deposition, landslide reactivation and riverbank erosion. The disaster affected five districts, damaging approximately 7,570 buildings and impacting 8,317 households. The Rapid Damage and Needs Assessment estimated total disaster effects at US$2.70 billion and recovery needs at US$4.77 billion, with hydropower, roads and housing among the most affected sectors. The event demonstrates how interconnected geological and hydrological hazards can rapidly escalate into large-scale disasters. Climate-related glacier retreat may have contributed to slope instability, highlighting the need for integrated multi-hazard risk assessment, improved monitoring, early warning systems and risk-informed reconstruction to strengthen resilience in vulnerable Himalayan communities.