Sikkim flash flood | What melting Himalayan glaciers mean for India and the local ecology

Tsomgo, a glacial lake in Sikkim. The Central Himalayas, of which Sikkim is a part, have been most impacted by glacier loss. (Photo by Shiv's Fotografia via Wikimedia Commons)

Earlier this month, a flash flood in Sikkim killed at least 34 people, swept away bridges and roads, and damaged the state’s largest hydropower project, the 1.2 GW Teesta-III. Images released by the Indian Space Research Organisation confirmed that it was triggered by a combination of glacial lake outburst flood (GLOF) and excess rainfall.

The disaster once again highlighted the growing risk of GLOFs in the Himalayas. South Lhonak lake, the site of the GLOF in Sikkim, was already recognized as potentially hazardous. Scientists at the National Remote Sensing Centre had warned of a 42 percent chance of a GLOF in as early as 2013.

The Himalayan region has witnessed similar GLOF-related disasters in the past. A Nature report cites the 1926 Jammu and Kashmir deluge, the 1981 Kinnaur valley floods, and the 2013 Kedarnath outburst as examples.

Climate change and human activity are exacerbating glacier loss. Without human interference, glaciers would stabilize at slightly higher elevations and eventually stop losing mass.

- Dr Iqbal Khan, independent researcher

“Yet, there is limited research on Himalayan glaciers in comparison to polar or Alpine glaciers. This makes it difficult to monitor them and predict such events,” said Dr Iqbal Khan, an independent researcher, who has been studying glaciers in the Himalayan region for over a decade.

The Geological Survey of India lists 9,575 glaciers in the Indian Himalayas, of which 267 are over 10 square kilometres in area. As temperatures rise due to global warming, these glaciers are melting faster than ever.

A 2023 report by the International Centre for Integrated Mountain Development found that glaciers in the region disappeared 65 percent faster from 2011 to 2020 than in the previous decade. Based on current emissions trajectories, they are estimated to lose up to 80 percent of their volume by the end of the century.

Even if global warming is limited to a 1.5 to 2 degrees Celsius rise over pre-industrial levels, as agreed in the Paris Agreement, Himalayan glaciers could still lose a third to half of their volume by 2100. That’s concerning.

“Climate change and human activity are exacerbating glacier loss. Without human interference, glaciers would stabilize at slightly higher elevations and eventually stop losing mass. However, human-caused climate change is preventing glaciers from reaching a new equilibrium anytime soon,” says Dr Khan.

While the melting of one or two glaciers may not seem much, cumulatively, the losses are significant. Himalayan glacier loss in the past 20 years equals the weight of 570 million elephants, as per a 2023 study published in the journal Nature Geoscience. It further adds that the number, area, and volume of proglacial lakes in the region has increased by 47 percent, 33 percent, and 42 percent, respectively, with the Central Himalayas, of which Sikkim is a part, being the most impacted.

“Climate change is also turbocharging the creation of glacial lakes, which are naturally formed by retreating glaciers. Many glacial lakes are also likely to develop in remote locations, and their presence may only be noticed in satellite images that reveal changes over time,” says Abhay Singh, an independent glaciologist. These lakes can burst when they fill beyond their capacity or are impacted by external forces such as earthquakes or excess rainfall.

Brace for impact

The impact on communities downstream and local ecology is tremendous. A 2020 study concluded that the numerous glacial lakes in the Indian Himalayas pose a serious threat to downstream communities. A GLOF causes water to flow at extreme speeds, causing massive damage to infrastructure. Areas for many kilometres downstream also become non-habitable after such an event.

The long-term impact, however, is deeper. Glaciers in the Himalayan region are a crucial water source for around 240 million people in the mountains and another 1.65 billion in the river valleys below. They feed 10 of the world’s most important river systems, including the Ganga, Indus, Mekong, and Irrawaddy, and directly or indirectly supply billions of people with food, energy, and income.

Climate change is turbocharging the creation of glacial lakes, which are naturally formed by retreating glaciers.

- Abhay Singh, independent glaciologist

Retreating glaciers also leave behind barren land and rubble. This can fragment the habitat. This can impact species such as snow leopards, the Himalayan tahr, and red pandas, making it difficult for them to survive and reproduce. Additionally, the loss of glaciers can reduce the availability of water and food that they, and other species, need to thrive.

“It’s already causing changes in the distribution of plant species in the Himalayas. Some plants that are adapted to colder climates are being replaced by plants that are more tolerant of warmer temperatures. This is leading to changes in the structure and composition of plant communities,” Singh.

Glaciers disappearing at an unprecedented rate means there will be devastating consequences for people and nature. Which is why it is important to take steps to mitigate the effects of climate change and anthropogenic impact, and protect them.