Holding Back the Flood Waters: The Draining of Northern Bhutan’s Glacial Lakes

The Lunana area of Northern Bhutan is surrounded by a stunning array of pristine mountains and the glaciers that move slowly through them. Amidst this serene beauty, however, is a growing danger that has the potential to be cataclysmic. As the ancient glaciers melt, their runoff collects and eventually forms pools of water known as glacial lakes. These pristine pools normally pose no danger to the surrounding villages, agricultural fields, temples, and schools. Recently, however, climate change has caused some of these lakes to grow substantially in size, posing a massive risk to the surrounding community.   

This risk is more generally known as glacial lake outburst floods and since the latter part of the 20th century, occurrences of them have continually increased.  These floods are massive discharges of water from glacial lakes, oftentimes resulting from weakened lake walls and increased glacier melt due to rising temperatures, warmer summers, or less intense winters. Much like the bursting of a man-made dam, the consequences of a glacial lake outburst can be devastating for local communities.   

Thorthormi Lake is one of many lakes in the Lunana region that has swollen in the last few years. Between 2001 and 2009 alone the lake nearly tripled in size, growing from 1.28 sq km in surface area to 3.42 sq km, making it by far the largest glacial lake in Lunana. This is a direct result of climate change speeding the melting of the Thorthormi glacier that feeds the lake. Thorthormi Lake has swelled to such a point that it is has been rated one of Bhutan’s most likely future catastrophes. Such an outburst through Thorthormi’s unstable walls would release up to 14 million gallons of water (53 million cubic meters if it overflows into the lower Rapstreng Tsho Lake) and debris into the surrounding communities, affecting an estimated 117 buildings, 16 historical monuments, a significant swath of agricultural land and infrastructure, and the lives of almost 400 people. In other words, this is an extremely serious threat to the region.   

Recently WWF and partners undertook a risky operation to drain Thorthormi Lake (which is perched at 14,527 ft above sea level). Draining the now massive lake is the first phase of an international project to reduce the risk to communities living in the nearby Bhutan valley.  A team of over 300 workers from 20 districts of Bhutan and from all walks of life — tourist guides, farmers, and yak herders — walked for up to 10 days to reach the site and dig and realign existing outlet channels to safely drain water from the lake.  The team braved thin and frigid air and harsh weather conditions including the assault of Cyclone ‘Aila’ in May 2009.  The heavy rains from the cyclone damaged access to the site and required immediate repairs before work could continue.    

While substantial progress was made, it was far from easy. The bad weather and extreme climatic conditions forced the team to lower their drainage goal for the first stage. However, by the close of this drainage season the team had managed to lower the water level of the massive lake by a little less than 3 feet. This slow, but steady, progress is only the beginning, as the work is scheduled to resume next spring and will continue until 2012, with a goal of lowering the water level by 16 feet.   

Glacial floods are not a merely theoretical threat to the Bhutan valley and its inhabitants. The community still bears the scars of a smaller flood in 1994 that took more than 20 lives, devastated villages and wrecked transport and power facilities. Since this first disaster, the monitoring of glaciers and their lakes has intensified. This monitoring has shown that Thorthormi Lake, only one of the lakes being fed by this glacier, has nearly tripled in size since 2001, while the natural dam holding it in has halved its height at its tallest point over roughly the same period. Amazingly, Thorthormi Glacier had no melt pools at all in the 1950s.   

The work of those draining Thorthormi Lake is a sobering example of the costs of delaying action on climate change. Adapting to the impacts of climate change in most cases will not be easy and will take significant investments of time and resources. However, as frightening as some of these impacts may be, the work in Northern Bhutan is proof that communities can work together to protect themselves.   

This post was based on information from a report written by WWF’s Living Himalaya’s Initiative entitled The Cost of Climate Change: The Story of Thorthormi Glacial Lake in Bhutan.

The Royal Government of Bhutan is monitoring the growth of the glacial lake with Japanese assistance. The drainage project is a large effort by the government, communities and WWF, supported by the Global Environment Facility (GEF), the United Nations Development Programme (UNDP) and the Austrian Coordination Bureau.