Nepal’s Deadly Floods Reveal the Growing Threat of Cascading Hazards in the Himalayas

The cause remains under investigation. ICIMOD Director General Pema Gyamtsho stressed that emergency response must take priority, with understanding the flood’s trigger essential to reducing future risks.

A flash flood that swept through central Nepal's Budhi Gandaki River system on 11 October has brought renewed attention to the dangers facing mountain communities, where a collapsing slope can trigger destruction far downstream.

Preliminary accounts from Nepal's authorities, reviewed by the International Centre for Integrated Mountain Development (ICIMOD), suggest the flood may have started when a temporary river blockage formed by a landslide gave way. Initial reports described missing people and considerable damage to homes, bridges and hydropower infrastructure. Authorities issued warnings to communities along the affected rivers.

The cause remains under investigation. ICIMOD Director General Pema Gyamtsho stressed that emergency response must take priority, with understanding the flood's trigger essential to reducing future risks.

Mountain disasters can set off a chain reaction

The flood follows the devastating Gyirong-Rasuwa disaster on 26 August, when a huge mass of rock and glacier ice broke away from a mountainside at around 5,200 metres. It crashed into the valley, sending water and debris through the Lhende River and Bhote Koshi system, destroying mountain communities and causing extensive loss of life.

Such events show how mountain hazards can build on one another: a slope collapse can block a river, and the failure of that blockage can release a powerful flood into settlements and infrastructure downstream.

Experts identified glacier retreat, thawing mountain permafrost and damage from a powerful earthquake more than a decade earlier as likely contributors to slope instability. Unusually high temperatures before the August collapse may have accelerated melting, with a greater share of precipitation falling as rain instead of snow potentially adding to the danger.

The broader changes are substantial. WMO's State of Global Water Resources 2025 report found that every glaciated region worldwide recorded net ice loss in 2025, marking the fourth consecutive year of global net losses across these regions.

A warning only works when people can act

These challenges shaped an international webinar on 7 October, hosted by the Associated Programme on Flood Management, a joint programme of WMO and the Global Water Partnership Organisation. Experts examined how early warnings, governance and preparedness can reduce cascading flood risks.

Nepal has improved its hydrological monitoring and forecasts for riverine and flash floods, but sparse observation networks in remote mountain areas still make sudden hazards difficult to detect and predict.

Bibhuti Pokharel of Nepal's Department of Hydrology and Meteorology described the gap between receiving a warning and responding to it. During the Bhote Koshi flood, SMS alerts reached residents, but some doubted the danger because they had never experienced anything comparable. Others approached flood-prone areas to take photographs or videos. The flood moved so quickly that many people had little time to act.

Warnings need clear instructions, evacuation routes, safe shelters and communities that know what to do. Trusted information from national meteorological and hydrological services is crucial, particularly when unverified reports and AI-generated misinformation can create confusion and delay decisions.

Regional progress comes with persistent risks

Figures presented by ICIMOD hydrologist Manish Shrestha, drawing on EM-DAT data, showed recorded disasters in the region rising from 864 in 1986–2005 to 1,148 in 2006–2025. Reported deaths fell from 272,085 to 231,470, and injuries declined from 1.17 million to 0.21 million.

The figures indicate progress in reducing human losses, though the continuing death toll underlines the scale of the challenge. Rivers cross national borders, making timely information exchange between upstream and downstream countries essential.

Kyrgyzstan faces comparable risks from glaciers, high-altitude lakes and permafrost. Its meteorological service highlighted the need to monitor dangerous lakes, improve modelling and strengthen institutions responsible for assessing and responding to hazards.

Switzerland's 2025 ice and rock collapse at Blatten offered another lesson: scientific observations must connect directly to coordinated warnings, decisions and early action.

Preparedness needs lasting investment

The webinar's priorities included better high-altitude observations, glacier and permafrost monitoring, real-time data collection, hydrological modelling and warning systems covering multiple hazards.

Sustained funding must support these networks alongside resilient infrastructure, community preparedness and cross-border cooperation. Linking climate finance with investment planning can help countries prepare before disaster strikes.

Early warning is essential, but protecting mountain communities also depends on effective governance and people having the knowledge, time and support to reach safety.