Chhimi Dema 

The glaciers, up in the mountains of Bhutan, are retreating fast. Every year, about  1,146.16 million tons of ice are lost from the glaciers of Bhutan.

This is the grim fact officials of the National Centre for Hydrology and Meteorology (NCHM) presented yesterday in Thimphu based on research and studies their glaciologist conducted.

Globally 1.2 trillion tons of ice are lost because of global warming every year rising the sea level. Glaciologist with NCHM, Karma (popularly known as Toeb Karma), at a media briefing yesterday said that under the current climate scenario, the average glacier retreat rate is accelerating.


Gangju La glacier

Gangju La glacier is a benchmark glacier (glacier recognised for long-term study) at the headwater of Pho chhu with a surface area of 0.2013km2 and a length of 0.9km. It has a thickness of 96.44 meters at its ridge.

Gangju La is retreating at an average rate of 13.1 meters every year.

The total retreat at the glacier’s terminus (glacier’s toe or snout) from 2004 until this year was 235 metres. Comparing the glacier mass added and mass loss, the total cumulative loss from 2004 to 2022 is negative 32.37 metre water equivalent. In other words, glacier loss is more than the glacier formed.

The annual glacier mass balance of Gangju La is negative 1764.68 millimetres at water equivalent. Mass balance is the change in the mass of a glacier or ice body, or part thereof, over a stated time. Water equivalent represents the volume of water that would be obtained from melting the snow or ice.


Thana glacier

The situation is no better at Thana, another benchmark glacier recognised in 2017.

The glacier is retreating at 23 meters every year. The terminus has also retreated by 952 meters from 1980 to 2022. Thana glacier has a mass balance of negative 1948.32 mm water equivalent from September 2021 to 2022. Total cumulative mass loss is negative 12.83 meters water equivalent.

Thana glacier is located at the headwater of Chamkhar chhu. It has a surface area of 3.65 km2 and a length of 2.75km and 228.86 meters thick.

Toeb Karma said that the Eastern Himalayas where Bhutan is located is sensitive to climate change. “If there is a rise in temperature even by one degree Celsius, the chances of solid precipitation such as snow becomes low and it will occur as rain which has a negative impact on the glaciers.”

The glaciers of the eastern Himalayas are influenced by the monsoon. Toeb Karma said that by the time the monsoon reaches the western Himalayas the strength weakens because most of the precipitation is shed off in the eastern Himalayas.

Glaciers in the eastern Himalayas are termed summer accumulation type glaciers. The 700 glaciers in the country cover 629.55 km2 of land which is 1.64 percent of total land cover.

The highest number of glaciers is found at the Pho chhu sub-basin with an area of 252.42km2. Glaciers and glacial lakes serve as sentinels of climate change and are giant freshwater reservoirs.

NCHM recognised Shodug located at the headwater of Thim chhu as the new benchmark glacier this year. Officials said that the mass balance cannot be determined since data of two years is required to calculate it.


Glacial lakes

There are 567 glacial lakes in the country covering an area of 55.04 km2 of which 17 are potentially dangerous.

NCHM officials carry out monitoring of potentially dangerous glacial lakes, update the list, and assess other glacial lakes yearly.

This year, NCHM carried out a study of Burtsham lake at the base of Gangkar Phuensum.

Geologist Phuntsho Tshering said the lake was growing as seen from the satellite images. In 2015, a similar study was carried out estimating the lake water volume, mapping the bottom topographic features and repeat photography.

“From 2015 to 2022, the water volume of Burtsham lake increased by 0.28 million m3. The lake depth increased by 8 meters and the lake area increased by 0.1 km2,” he said.

Phuntsho Tshering said that by considering the size of the lake, water content and other factors such as surrounding and bottom topography, there is no immediate danger [of GLOF] but regular monitoring is recommended.

The Intergovernmental Panel on Climate Change report discusses the loss of glacier mass as a consequence of climate change and points out that the pace of this retreat is significantly faster than noted before.

The report states that such changes have serious consequences on the water cycle, water volume and supply, increased food insecurity, and more water-related hazards such as floods and landslides.