An analysis said the recent Nepal flood, in which a "wall of water and mud" swallowed buildings in an instant, was a type that is hard to predict with existing monitoring systems.
The New York Times (NYT) reported on the 28th, citing geologists, that the flash flood that struck Nepal and Tibet on the 26th occurred when a landslide in high terrain and a glacier collapse unleashed a massive volume of water all at once.
Disaster experts agree that this type of event is especially hard to predict. Current glacier risk monitoring systems mostly focus on specific danger zones such as watching the water level of glacial lakes. They estimate flood timing and downstream risk through real-time video monitoring, laser water-level measurements, and on-site observations.
But experts said that detecting a sudden collapse of part of a mountain, like this time, requires monitoring a much wider area, which demands enormous resources.
Aaron Hood, a professor at the University of Alaska, proposed combining seismic activity measurements with remote sensing to build 3D imagery of high-risk areas, but noted, "The Himalayas are extremely remote, so even getting drones or helicopters in is not easy."
According to a 2020 report by an intergovernmental body that monitors mountain regions, Nepal has 2,070 glacial lakes, 21 of which are classified as high risk. Many glacial lakes are also distributed in the Himalayan regions of neighboring China and India.
Nepal operates a flood warning system, but because it relies on conventional river and lake gauge networks, it can detect gradual rises in water levels yet was outside the response scope for a situation like this, where a torrent formed in an instant.
Sushil Kumar Shrestha of Nepal's National Disaster Risk Reduction and Management Authority said, "The warning system worked, but the flood unfolded too quickly to allow enough time to evacuate." The Chinese side did not disclose details of its own monitoring system.
Alton Byers, a glacier risk expert at the University of Colorado, suggested that in situations where real-time alerts are impossible, alternative measures are needed, such as restricting construction in floodplains and developing and marking evacuation routes in advance so residents become familiar with them.