KATHMANDU: China’s government weather agency has attributed the flash floods and debris flows in northern Nepal to heavy rainfall in Nepal and the upper catchment areas of southern Tibet.
The Beijing-based World Meteorological Centre published the analysis in the 92nd issue of its Global Disaster Weather Monitoring and Forecast News on August 26, under the headline “Flash Flood Disasters Occur in Northern Nepal.”
According to the report, Nepal had experienced continuous rainfall for around 10 days due to the southwest monsoon and the Himalayan terrain. Accumulated rainfall during the period reached heavy to extremely heavy levels in some areas.
The report also noted moderate to heavy rainfall, with locally heavy to extremely heavy rain, in southern Tibet, which forms part of the upper catchment connected to northern Nepal. The rainfall there was influenced by a plateau trough.
Rainfall on both sides of the border
The Chinese weather agency said the flash floods and debris flows in northern Nepal on August 26 were influenced by rainfall both within Nepal and in southern Tibet.
The assessment can be considered in the context of the sudden rise in water levels in the Bhote Koshi River and flooding in the Lhende Khola and Rasuwagadhi areas.
However, the report does not identify a specific glacial lake outburst, avalanche or glacier collapse as the immediate cause of the flooding in Rasuwa.
In other words, the Chinese report primarily analyses the meteorological conditions surrounding the disaster. It does not establish how such a large volume of water and debris entered the Lhende Khola so suddenly.
More heavy rain forecast
The Chinese weather agency also issued a three-day weather outlook on the day of the disaster.
It forecast continued moderate to heavy rainfall across Nepal, with heavy to extremely heavy rainfall possible in southern parts of the country due to a monsoonal low-pressure system over northern India.
The agency warned that continued heavy rainfall could trigger further flash floods, landslides and debris flows.
The report includes maps showing accumulated rainfall from August 16 to 25, atmospheric conditions on August 26, and the rainfall forecast for August 26 to 29.
Different explanations under study
Several preliminary explanations have emerged regarding the cause of the Rasuwa floods, including an avalanche, a glacial lake outburst, a glacier collapse or the temporary blockage of a river followed by a sudden release of water.
The Chinese weather agency’s report, however, does not conclude that any one of these geological events caused the disaster. Its analysis focuses mainly on rainfall and atmospheric conditions.
Meanwhile, Nepal’s National Disaster Risk Reduction and Management Authority has presented a different preliminary finding based on Planet Labs satellite imagery.
According to the authority, an ice-rock landslide occurred around 20 kilometres northeast of the Rasuwagadhi border point along the Nepal-China border. The landslide appears to have sent a large volume of debris and water into the Lhende Khola, with the resulting flood flowing through Timure and into the Trishuli River.
The satellite analysis reportedly shows the landslide and subsequent flooding between August 25 and 26.
The two assessments point to different aspects of the disaster: the Chinese report highlights the heavy rainfall and broader weather conditions, while Nepal’s disaster authority has identified an ice-rock landslide and debris flow as a possible direct trigger. A detailed geological and hydrological investigation will be needed to determine the full chain of events.
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