NGAWANG JAMPHEL
Thimphu
Bhutan is home to about 700 glaciers, located in the eastern part of the great Himalayan range. Although these glaciers occupy only 629.55 square kilometers—just 1.64% of Bhutan’s total land area—they play a crucial role in maintaining the country’s water resources.
To understand how glaciers in Bhutan are changing, the Cryosphere Services Division under the National Centre for Hydrology and Meteorology (NCHM) has started a long-term glacier monitoring program.
As part of this program, three main glaciers—Gangju La, Thana, and Shodug—have been selected as benchmark glaciers. These glaciers are clean-type glaciers, meaning they have little or no debris (rocks and dirt) on their surface.
Each glacier is located in the headwaters of major rivers: Gangju La in Pho Chu, Thana in Chamkhar Chu, and Shodug in Thim Chu.
The NCHM has been studying the changes in these glaciers using two main methods: the direct (glaciological) method, which involves taking field measurements from the glacier itself, and the geodetic method, which uses satellite and aerial images.
The changes being observed include the retreat of the glacier terminus (the end of the glacier) and reduction in glacier area.
For instance, the Gangju La glacier has been studied from 2004 to 2020, while the Thana and Shodug glaciers have been observed from 1990 to 2020.
The results show that all three glaciers are shrinking. Their retreat has increased in recent years, which means that glaciers are melting faster now than they were 20 or 30 years ago.
Interestingly, the study also found that glaciers in the eastern part of Bhutan are melting faster than those in the west. This could be due to differences in local weather and temperature conditions.
Over the past 30 years, the glacier area has decreased by 15% to 30%. These changes are mostly due to rising temperatures caused by climate change. Although there may be other reasons like local weather conditions, more scientific research is needed to confirm them.
Another important part of glacier monitoring is measuring mass balance. This tells us whether a glacier is gaining or losing ice overall. A negative mass balance means the glacier is losing more ice than it is gaining, which is not good. Gangju La has been monitored since 2003, Thana since 2015, and Shodug was added in 2021.
According to the data collected, all three glaciers are showing negative mass balance values, meaning they are losing ice every year. The mass loss has been quite high in recent years. Even though there are small variations from year to year, the overall trend is a steady and sharp decline.
This, according to NCHM, is clearly shown in the cumulative mass balance graph, which shows how much ice has been lost since monitoring began.
This loss of glacier ice not only threatens Bhutan’s water supply but also increases the risk of glacial lake outburst floods (GLOFs). When glaciers melt, they form lakes at their base. If these lakes grow too big or are blocked by unstable ice or rocks, they can burst suddenly, causing floods downstream.
According to the Bhutan Glacial Lake Inventory (2021), there are 567 glacial lakes in Bhutan, spread mainly across the northern parts of the country. These lakes cover an area of 55.04 square kilometers, which is about 0.14% of Bhutan’s total land.
The Manas River Basin has the highest number of glacial lakes—331 lakes covering an area of 29.2 square kilometers—while the Wang Chhu Basin has the least, with only 31 lakes covering 0.6 square kilometers.
Out of the 567 glacial lakes, 17 have been identified as potentially dangerous glacial lakes (PDGLs). These lakes are considered risky because they could burst and cause major flooding.
This list was updated in 2019 after conducting ground verification. The earlier list, prepared in 2001 by ICIMOD (International Centre for Integrated Mountain Development), had 25 lakes marked as dangerous.
However, some of them were later found to be stable and were removed from the updated list. Among the river basins, the Pho Chu sub-basin has the highest number of PDGLs.
Bhutan’s glaciers are under serious threat due to climate change. The shrinking glaciers and growing glacial lakes highlight the urgent need for continued monitoring, scientific research, and climate action.
Glaciers are large, slow-moving bodies of ice that form over many years from layers of snow. In Bhutan, glaciers help maintain water flow in major rivers such as Pho Chu, Mo Chu, Thim Chu, and Chamkhar Chu.
Studies have shown that glacier meltwater contributes between 33% to 49% of the surface flow in these rivers. This is especially important during the dry winter months when there is less rainfall.
Apart from providing water, glaciers also help regulate temperature. Their bright surface reflects sunlight, which keeps the surrounding areas cooler.
However, due to global warming, glaciers around the world are melting faster than before. Rising temperatures are causing glaciers to shrink in size and lose mass. Bhutan’s glaciers are also facing the same problem.
