As emergency workers searched Himalayan valleys on Thursday for survivors of a colossal flood that killed hundreds of people, the Nepali and Chinese authorities warned that a second flood might be coming — with rescuers most at risk, according to an expert.
The landslide that set off Wednesday’s flood clogged the river system and created a barrier lake close to the border between Nepal and the Tibet region of China, the Chinese Ministry of Water Resources said Thursday evening. It said that rain forecast to fall over the next three days could more than double the lake’s water volume to over 176 million cubic feet, the equivalent of about 2,000 Olympic-size swimming pools.
The risk that the new lake could breach its rocky barrier and wreak havoc downstream was “high,” the ministry said, potentially causing areas such as the Gyirong border crossing, which had already been decimated by floodwaters, to be “struck by disaster again.”
The lake had already started to overflow on Thursday, forcing rescue efforts in Tibet to stop and sending water into the same river that flooded a day earlier, Chinese state broadcaster CCTV reported on Friday morning.
Nepal’s disaster management agency on Thursday urged people to move away from riverbanks because of the risk of a second flood.
Another deluge would track the same path as the first, posing the most risk to people on search-and-rescue missions, said Austin Lord, an anthropologist and senior fellow at the Stimson Center in Washington, who has studied natural disasters in Nepal.
A second flood would be another challenge for rescue and assistance efforts already forced to navigate destroyed infrastructure and damaged communication lines. “Warnings of potential renewed floods are complicating an already challenging operation,” said David Fisher, head of delegation for International Federation of Red Cross and Red Crescent Societies in Nepal.
While the flood would most likely be smaller and significantly less deadly, Mr. Lord said, the volume of water in the new lake is “not insignificant.” He compared its potential impact to that of a flood that hit the same area last year, killing at least eight people, destroying a key border bridge and disrupting trade between Nepal and China.
“We have no way of knowing how the dynamics would play out,” Mr. Lord said. “The area is so freshly volatile.”
But governments, residents and rescuers would have a crucial advantage this time: a heads-up.
“They’re running models of potential floods and visually monitoring the growth,” said Alton C. Byers, a senior research associate at the Institute of Arctic and Alpine Research at the University of Colorado, Boulder. “They can warn people.”
The Himalayas are dotted with thousands of glacial lakes, posing a constant flood risk if large, falling debris crashes into them. The region is known for being prone to natural disasters.
Scientists have said the deadly flood on Wednesday was probably caused by a massive rock landslide colliding with a glacier falling from the high mountains.
Mr. Lord said scientists were also monitoring what seems to be yet another new body of water forming at the initial impact point below the north face of Langtang Lirung, a mountain in Nepal near the border with China.
“It seems to have created a glacial lake that’s growing in size,” Mr. Lord said. “It may overtop or breach at some point in the coming days.”
Lily Kuo and Mujib Mashal contributed reporting.
