Human-induced climate change contributed to August 26 Nepal disaster: Study

Kathmandu, Sept 19: Human-induced climate change, along with geological and climatic factors, likely contributed to the catastrophic disaster that struck Nepal on August 26, according to a study by the World Weather Attribution (WWA).

The study, released on September 17 under the title “Rapid Warming in the Himalaya Exacerbates Geohazard Cascades Beyond Adaptation Limits,” examined the factors behind the massive rock-ice avalanche and subsequent debris flood along the Nepal-China border in Rasuwa.

Researchers said long-term warming and permafrost degradation likely weakened the mountain slope by increasing bedrock temperatures and thawing ice within rock fractures. The resulting meltwater may have increased water pressure and further destabilised existing geological weaknesses.

The study also pointed to the possible long-term influence of the 2015 magnitude 7.8 earthquake. While researchers said its specific role in the August 26 disaster could not yet be confirmed, they noted that the earthquake may have weakened the underlying rock mass and contributed to continued slope instability.

According to the researchers, the collapse of rock and glacier ice triggered a cascade of processes. As the avalanche moved rapidly down the mountain, friction and mechanical energy likely melted some glacier ice. The avalanche then encountered buried ice, adding further water to the debris flow.

The resulting mixture of water, ice, rock and sediment developed into a highly destructive debris flood that swept through settlements and infrastructure along the Bhotekoshi-Trishuli corridor.

Existing warning systems faced limits

The WWA study acknowledged that Nepal has established early warning systems and adaptation measures that can reduce the impacts of conventional river floods.

However, researchers said the August 26 disaster was fundamentally different in its magnitude, speed and complexity, exceeding the design and predictive limits of existing risk-reduction measures. They concluded that no existing early warning system could have provided sufficient lead time to prevent the scale of impacts in the worst-affected areas.

The study further noted that glaciers in the region have been losing mass for decades, while the Langtang-Lirung glacier has experienced accelerated retreat in recent years. Researchers said continued warming, glacier retreat and permafrost degradation could increase the risk of similar cascading hazards in high mountain regions.

At the same time, the researchers stressed that they had not determined that the August 26 rock-ice avalanche would have occurred in the absence of human-induced climate change. Instead, they described climate change as a destabilising factor acting on an already vulnerable geological setting.

The study called for stronger high-Himalayan hazard monitoring, improved risk communication, better transboundary data sharing and greater investment in climate adaptation and disaster preparedness.

Researchers from Nepal, Pakistan, the UK, Ireland, Sweden, Denmark, Norway, the United States, New Zealand and the Netherlands contributed to the assessment, bringing expertise in glaciology, mountain hydrology, climate science, seismology, humanitarian response and social science.