Glaciologist Warns of GLOF Threats in Bhutan
As he navigates the rugged terrain of Bhutan’s mountains, glaciologist Karma Toeb is troubled by the rapid changes in the environment. At an altitude of 4,500 meters, he is inspecting a fragile glacial lake. Over a shaky phone connection, Toeb expresses his concern: “The environment is changing so fast… I feel sad and angry because these changes bring many risks downstream.”
Bhutan, a nation that contributes little to climate change, bears a heavy burden. Toeb is leading a team in a remote area called Lunana, specifically at Thorthormi lake, as part of his 32nd visit since 1997. They are testing new technology to determine if it’s possible to drain the lake in order to reduce the risk of a glacial lake outburst flood (GLOF).
The potential dangers from Thorthormi and another nearby lake could jeopardize two significant hydropower projects. The Punatsangchhu-II project is already in operation, while Punatsangchhu-I is still under construction. Bhutan has been proactive in trying to safeguard its citizens and key hydropower infrastructure from such risks. This includes efforts to drain glacial lakes and improve its early-warning systems, which now focus on forecasting rather than just detecting floods.
The urgency of these efforts has increased following devastating flooding in neighboring Nepal and China on August 26, which resulted in nearly 1,500 deaths and damage to numerous hydropower plants. These events have amplified concerns in Bhutan about a possible GLOF from Thorthormi.
Hydropower plays a crucial role in Bhutan’s economy, contributing about 12-15% to its Gross Domestic Product (GDP) and accounting for around 40% of its exports and 36% of government revenue. The relationship between India and Bhutan is also closely tied to hydropower. India imports all of Bhutan’s hydropower, and both countries have collaborated for decades on developing dams and energy infrastructure.
In 2025, following the launch of Punatsangchhu-II, Bhutan’s electricity export to India reached BTN 24.3 billion (approximately US$285 million), contributing to a nearly 9% growth rate for Bhutan’s economy.
Michael Williamson, a representative from the UN Economic and Social Commission for Asia and the Pacific, emphasizes the need to consider a range of potential hazards, including ice and rock avalanches and landslides, in addition to traditional flooding risks. He suggests that new hydropower projects should conduct thorough assessments of these risks before moving forward.
Bhutan is primarily mountainous, and as temperatures rise, its glaciers are becoming increasingly unstable. Recent assessments show that the number of glacial lakes has surged from 567 to 620 in just five years, raising alarms about the potential risks associated with glacial flooding.
A study in 2024 estimated that a GLOF from Thorthormi could result in an enormous water discharge, inundating farmland and putting vital infrastructure at risk. While Raphstreng lake is stable, Thorthormi remains uncertain, according to Trashi Namgyal from the National Center for Hydrology and Meteorology.
Despite the risks, Bhutan’s energy cooperation with India is expected to continue. Dasho Chewang Rinzin, head of Druk Green Power Corporation, believes that while generation may need to be adjusted during extreme weather events, the overall energy cooperation will be resilient.
Recent floods in the region illustrate the significant threat posed by debris flows in addition to water levels. A former official highlighted concerns over heavy debris clogging power infrastructure, which resonates with the recent catastrophic flooding experienced in Nepal.
To mitigate GLOF risks, the team is testing new siphon technology to control reservoir drainage at Thorthormi. After a previous attempt failed, adjustments have been made for this latest effort.
Bhutan’s early-warning systems currently detect floods as they occur but are evolving towards a more proactive forecast-based warning system that takes into account weather conditions to give earlier alerts. In worst-case scenarios, floods could reach historical sites within a few hours, making timely evacuations essential.
As Bhutan plans for its energy future, the focus remains on integrating climate risks into hydropower project developments. The government has set ambitious targets for expanding its hydropower capacity by 2040 but faces challenges with an already significant hydropower debt.
Residents living near Thorthormi are deeply aware of the risks. Gup Kaka, a local villager, recalls the devastating effects when Luggye lake overflowed decades ago, highlighting the community’s ongoing fears related to GLOFs. Authorities are taking preventive measures, such as conducting evacuation drills, to ensure residents are prepared and aware.
In the face of changing environmental conditions, Bhutan strives for a balance between energy production and safety, reflecting both the challenges and determination of a nation vulnerable to climate impacts.
