According to the studies conducted by the National Center for Hydrology and Meteorology (NCHM), the three benched marked glaciers are losing mass continuously. A similar retreating trend is observed on the terminus of the glacier. Therefore, if all glaciers are exposed to the same kind of climatic and environmental conditions as benchmark glaciers, a total of 1146.16 million ton of ice are being lost annually from glaciers of Bhutan.
NCHM has considered Shodug glacier in Thimchu in the western part of Bhutan, Gangju la glacier located in the headwaters of Pho Chhu and Thana glacier located in the headwaters of Chamkhar Chhu as a representative or a benchmark glacier for long-term mass balance observation in Bhutan.
NCHM has carried out Mass Balance Measurement, Frontal/Terminus Mapping, Thickness Measurement, Snow Measurement and Repeat Photography to track the change of the glacier over time in these three glaciers.
The Director of NCHM Karma Dupchu said for Bhutan, glacial lakes are very important because it is a water resource, and also a driving economy of Bhutan. In light of climate change, although these are a resource, it becomes a hazard with the melting of glaciers, and there will be glacier lake outburst. Since all the settlements in Bhutan are along the river. So, therefore it is very important to monitor and set up an early warning system.
The Director also highlighted some of the challenges faced. The center does not have enough data and scientific instruments to understand the impact of climate change, and accessibility to glacial is very difficult as it takes almost a month to reach it.
The NCHM official said regarding the glaciers of Bhutan, they have carried out Bhutan glacial inventory 2018 using remote sensing technique, and there it found that there are a total of 700 glaciers, covering an area of 629.55 which comprising 1.64 percent of the total land cover, with the highest number of the glacier in Pho Chhu sub-basin.
Similarly, there are around 567 glacial lakes in Bhutan, which covers an area of 55.04 km2. The highest number of glacial lakes are under Punatshang Chhu (Pho Chhu). Out of which, there are 17 potentially dangerous glacial lakes.
The official said, “Since we have experienced a lot of disasters including the 1994 flood. So, when we find out some glacial lakes are dangerous or possess dangers then we have to go on mitigation and installation of an early warning system.”
Usually, the center carries out regular time series monitoring of those lakes, and especially the identified potentially dangerous glacial lakes. For example, there are a few glacial lakes in Lunana, so every two to three years or annually, the center does time series monitoring and assessment of other glacial lakes.
Whether the glacial lakes are dangerous or not, the experts check the lake surface area from the satellite images and then only they can go for an assessment. When they see the changes in glacial lakes’ surface area from the satellite images, and if the water volume is increasing, the expert visit there and then tries to extract the volume of water. For that, they use simple equipment called a Sonar which is attached to the boat when it sends the signal down then it reflects back and gives information about the depth of the glacial lake, said the official.
According to 2020 and 2022 field activity and satellite images, there is one glacial lake at the base of Gangkar Phuensum that is growing, and is attached to Burtsham glacial lake, so to keep track of changes, they have carried out the survey.
According to their survey, from 2015 to 2022, there is an increase in the lake water volume by 0.28 million m3, an increased lake depth by 8m and the area has been increased by 0.1 km2. The study found that there is no immediate danger but regular monitoring is recommended.