Preparing for a ‘tsunami in the sky’

Dorji Wangmo from Tencho village in Lunana, one of Bhutan’s northern-most regions, still vividly remembers how she and others in the community ran for their lives when a glacial lake outburst flood struck Lunana on 7 October 1994.

It was Bhutan’s first major glacial lake flood, triggered by the partial burst of Luggye glacial lake, one of four in Lunana.

The people of Lunana have since lived in constant fear of glacial lake flooding, and that fear is growing as the mountains become warmer and glaciers retreat rapidly due to climate change, and water builds up behind moraine dams.

At more than 4,000 metres above sea level, Lunana is one of the highest human settlements on Earth. Climate change is an everyday reality in this remote highland community that’s home to Baytsho, Raphstreng, Thorthormi and Luggye lakes. The latter three are among Bhutan’s 17 potentially dangerous glacial lakes.

Dorji Wangmo from Thanza, the village closest to the lakes, said the fear of flooding keeps her up at night. Villagers have only 20 minutes to evacuate or move to safer ground.

Tsunami in the sky

In 2008 the country launched the mammoth task of manually lowering Thorthormi lake to a safe level. The effort, supported by UNDP through the Global Environment Facility (GEF) funded National Adaptation Programme of Action, wrapped up in 2012. Early warning systems were put in place and communities’ disaster preparedness and response improved. This was preceded by a three-year project to lower Raphstreng lake by four metres.

Worst case scenario

The 1994 flood claimed lives, destroyed homes, farmland and infrastructure. A much more severe disaster is brewing in Lunana, says glaciologist Karma.

More than a decade after the work at Thorthormi, the threat has doubled as warming temperatures cause glacier meltdown. Bhutan has 700 glaciers, and they are retreating fast, according to the National Center for Hydrology and Meteorology. The Gangju La Glacier in the Pho Chhu basin, at an altitude ranging from 4,800 – 5,100 metres above sea level, has retreated at an average rate of 11.4 metres per year from 2004 to 2019. And Thana Glacier, at an altitude ranging from 5,100-5,700 metres above sea level, in the Chamkhar Chhu basin, has recorded an average retreat of 18.2 metres annually.

The glaciers are shrinking at a speed never seen before, and they risk triggering what Bhutanese glaciologists aptly describe as a ‘tsunami in the sky’. Of the 567 glacial lakes in the country, 17 have been identified as potentially dangerous.

Thorthormi is in its forming stage. Small ponds of melted glaciers are slowly converging into a large lake.

Just below Thorthormi, separated by a thin moraine dam containing ice core, lies the Raphstreng lake. Scientists have long raised concerns over the structural strength and stability of the moraine dam.

Glaciologist Karma said a lot of mass movements are taking place in both the lakes every year, causing the thinning of the moraine dam barrier. The unsteady moraine dam measured 33 metres on the thinnest parts in 2021.

And that is about four times more severe than the 1994 flood and will cause devastating damage to lives, properties and infrastructure, including two of the country’s biggest hydropower power projects located downstream. 

Climate change is our reality

“It scares me when I hear of what climate change is doing to our country. Why wouldn’t I be scared? We live just next to the lakes. If the glaciers continue to melt at the current rate, there will come a day when we have no water. Snow fall has become rarer already,” said Dorji Wangmo.

The thinning of glaciers in Bhutan and across the world has become a new reality as the global climate crisis intensifies. Bhutan and its people, despite doing little to cause climate change, are bearing the brunt of the crisis.

The recent Intergovernmental Panel on Climate Change report warns the glaciers in the whole of the Hindu Kush Himalayan region will keep shrinking with cascading consequences of floods and landslides if the world fails to slash emissions drastically.

For Dorji Wangmo, the majestic, snow-covered peaks becoming bare rocks is unimaginable. “If the snow melts and our mountains become bare rocks, Lunaps will be gone too. When the weather is clear and mountains glisten in the sun, we say, 'Oh! what a beautiful sight.' We have always lived with glaciers and would like to continue living like that. The mountains look nice with snow cover. It would be sad to see them without snow cover.”