Bhutan faces heightened glacial lake outburst flood risks from climate-driven glacier melt, with new research revealing over 11,000 people and vital infrastructure now exposed to potential catastrophe.
Bhutan, nestled in the eastern Himalayas, is confronting one of the most immediate and severe impacts of global warming: the rapid expansion and destabilization of glacial lakes. A recent study published in the science journal website, phys.org, highlights significantly elevated risks of Glacial Lake Outburst Floods (GLOFs), events where natural dams fail, unleashing massive volumes of water downstream with devastating speed and force.
As of 2021, Bhutan inventories 567 glacial lakes, many formed or enlarged by retreating glaciers. These lakes, perched high in remote valleys like Lunana, are expanding due to accelerated ice melt driven by rising temperatures. Glaciers in Bhutan are receding at rates of 30-60 meters per decade, far outpacing many other Himalayan regions.
New Study Reveals Expanded Risks
Published findings from advanced modelling indicate that previous assessments underestimated the dangers. Researchers simulated hypothetical GLOF scenarios for lakes larger than 0.05 km² near glacier termini. The results are alarming: approximately 11,322 people, 2,613 buildings, 270 km of roads, 402 bridges, 19 km² of farmland, and even 4 hydropower dams lie in potential flood paths.
Median GLOF travel distances reach 40 km, with inundation areas averaging 2.9 km². Flow depths and velocities can hit 3.3 meters and 3.4 m/s respectively, arriving at vulnerable sites in as little as 8 minutes in some cases. Collectively, these events could affect about 2 per cent of Bhutan’s land area.
Thorthormi Tsho (also spelled Thorthomi) emerges as the most critical threat – classified as a very high hazard lake. Located in the Punatsangchu basin at over 4,000 meters, this supraglacial lake has grown dramatically. Past partial outbursts, including events in 2019 and 2023, underscore its instability. A full breach could release enormous volumes, impacting over 1,100 buildings, 72 km of roads, and 4.2 km² of farmland alone.
Five other lakes rank as high hazard, including newly identified ones like Phudung Tsho, lake251, and Wonney Tsho, which prior studies overlooked. 22 additional lakes fall into the moderate hazard category. Five local government units face very high GLOF risk, with eight more at high risk – several previously unrecognised.
Historical Precedents and Human Impact
Bhutan has recorded at least 18 GLOFs in the last 70 years. The deadliest occurred in 1994 from Lugge Tsho in the Lunana region, claiming over 20 lives, damaging the historic Punakha Dzong, and destroying homes and infrastructure downstream.
More recent events, such as the 2015 Lemthang Tsho outburst and partial releases from Thorthormi, caused localized damage but served as warnings. Communities in valleys like Punakha-Wangdue and Chamkhar remain particularly vulnerable, relying on agriculture, roads, and hydropower – sectors central to Bhutan’s economy and Gross National Happiness framework.
Downstream impacts extend beyond immediate flooding: sediment-laden waters can bury farmland, erode riverbanks, damage bridges critical for connectivity in this mountainous terrain, and disrupt power generation. With Bhutan’s population concentrated in river valleys, the human toll could be significant despite proactive measures.
Bhutan’s Proactive Response
Despite being a carbon-negative country – absorbing more CO₂ than it emits through vast forest cover – Bhutan is disproportionately affected by climate change due to its high-altitude geography. The government, in partnership with international organizations like UNDP and ICIMOD, has implemented mitigation strategies.
Notable efforts include the artificial lowering of Thorthormi Lake between 2008 and 2012, involving manual siphoning and engineering works to reduce water levels. Early warning systems with sirens and automated monitoring have been expanded. Technicians endure harsh conditions in Lunana to provide round-the-clock surveillance.
Recent initiatives involve further siphoning pilots and enhanced risk assessments. The National Centre for Hydrology and Meteorology (NCHM) leads inventories and modelling, while community awareness programmes prepare residents for evacuation. Five local government units identified in the latest study as high-risk are prioritized for strengthened preparedness.
Broader Context of Himalayan Glacial Change
The situation in Bhutan mirrors trends across the Hindu Kush Himalaya (HKH) region, often called the Third Pole. Glaciers here feed major rivers sustaining nearly 2 billion people. Warming has increased lake formation, with lake-terminating glaciers retreating faster. Black carbon deposition from regional pollution may further accelerate melt.
Projections under various warming scenarios suggest continued glacier area loss exceeding 50 per cent in some models, threatening long-term water security for hydropower – a pillar of Bhutan’s economy – and agriculture. GLOFs are not isolated; they interact with monsoons, landslides, and earthquakes, compounding risks.
Comprehensive monitoring complicated
Remote terrain, limited resources, and the sheer number of lakes complicate comprehensive monitoring. While engineering solutions like lake lowering help, they are costly and temporary amid ongoing warming. International funding and cooperation are essential, as highlighted in global forums.
Experts recommend integrating detailed inundation mapping with exposure and vulnerability data for better prioritization. Expanding early warning systems, reinforcing infrastructure, and diversifying livelihoods in high-risk zones are key. Bhutan’s focus on sustainability offers a model, but global emissions reductions remain critical to slowing the underlying driver: climate change.
