Bhutan glacier monitors track rising flood risk

Bhutan is using round-the-clock monitors, sensors and evacuation sirens to track the risk of floods from melting Himalayan glaciers.

The warning centre in Wangdue Phodrang region began work in 2011 after a deadly 1994 glacial lake outburst flood killed 21 people along the Punatsangchhu river, also known as the Sankosh.

Glacial lakes can form as climate change melts glaciers. If the fragile debris walls holding them back collapse, the water can surge downstream into communities.

Bhutan has more than 600 glaciers and more than 600 glacial lakes, with 17 lakes considered potentially dangerous. Some of the most dangerous are at the head of a river feeding into the Punatsangchhu.

Dechen Peldon, a junior engineer at the GLOF emergency warning facility, said the Thorthormi glacier had fully transformed into a glacial lake because of climate change. She said the recent disaster on the Nepal-Tibet border had made control room operators more vigilant.

The centre oversees sensors that detect changes in water levels at glacial lakes and downstream rivers. Sirens in the nearest communities can be triggered automatically if water levels suggest a possible glacial lake outburst flood. Sirens farther downstream are triggered manually by the team if dangerous changes are detected.

In a worst-case scenario described in the area, a debris wall separating two lakes could collapse and release an estimated 53 million cubic metres of water downstream. Nearby communities would have only minutes to evacuate.

Bhutan has also tried to reduce the danger upstream. In 2008, it began a years-long project to dig out and widen a channel from the Thorthormi glacier lake, lowering the water level by five metres. Karma, Bhutan's leading glaciologist, said continued melting had filled the lake again and experts are now trying to siphon water out.

Karma said Bhutan's largest glaciers are retreating by 30 to 35 metres a year, while smaller glaciers are retreating by about 12 to 16 metres a year. He said the risk to Bhutanese communities was unfair because the country absorbs more planet-warming carbon than it emits.