The Sikkim flash floods at South Lhonak Lake on October 3-4, 2023, were due to a phenomenon called a glacial lake outburst flood (GLOF). Numerous reports had previously warned about the lake’s high risk of a GLOF event, but unfortunately, these warnings were ignored.
The situation is worsened by two human-induced factors. First, extreme rainfall events caused by global warming, and second, the encroachment of human activities into floodplains. Both factors enhance the likelihood of future GLOF disasters.
South Lhonak Lake
- South Lhonak Lake, located 5,200 meters above sea level, is the largest and fastest-growing glacial lake in Sikkim.
- The lake has seen a glacial retreat of nearly two kilometers from 1962 to 2008.
- An additional retreat of the glacier by 400 meters was recorded between 2008 and 2019, escalating the risk.
- South Lhonak, being among the largest and quickest expanding glacial lakes in Sikkim, always posed a ‘GLOF’ or Glacial Lake Outburst Flood risk.
- The lake’s size increased over threefold, from 0.42 sq km to 1.35 sq km, between 1990 and 2019.
- As of 2019, Lhonak held around 65 million cubic feet of water.
- A 2021 study warned of an impending GLOF, which could lead to extensive damage downstream.
- Sikkim is home to fourteen other glacial lakes, each as large as South Lhonak. Each of these lakes also presents a potential hazard of causing substantial damage if a burst occurs.
Factors Leading To The Disaster
- A study titled “Future Glacial Lake Outburst Flood (GLOF) hazard of the South Lhonak Lake, Sikkim Himalaya” pointed out reasons for the lake’s vulnerability.
- Rapid lake growth due to glacial retreat over the past decades increased the risk of GLOF.
- The glacier’s size reduced from 6.4 km to 5.1 km in 29 years, shrinking by around 0.96 sq km.
- The Central Water Commission of the central government had issued an advisory to assess the lake system’s state.
- The study outlined several risk factors for South Lhonak.
- The lake’s expansion towards steep slopes increased the danger of landslides and avalanches.
- Being in a seismic zone further elevated the risk.
Impact Of Climate Change On Glacial Lakes In Sikkim Himalaya
- Researchers have identified climate change as a significant factor affecting Himalayan glaciers and glacial lakes.
- Studies have highlighted that glaciers are retreating at a rate between 10 and 60 meters per year.
- A 2012 study titled “Remote Sensing-based Inventory of Glacial Lakes in Sikkim Himalaya: Semi-automated Approach Using Satellite Data” revealed an increase in the number of glacial lakes in the Sikkim Himalayas.
- These lakes are found to be susceptible to Glacial Lake Outburst Floods (GLOFs).
- The International Centre for Integrated Mountain Development (ICIMOD) conducted a study in 2003, using satellite data.
- This study discovered 266 glacial lakes within the Sikkim Himalayas along the Teesta basin, covering an area of 20.20 sq km.
- Among these, 14 lakes were identified as potentially hazardous.
- Risks And Impacts Of Hydropower Projects In The Himalayas
- Recent disasters have raised concerns about the risks associated with hydropower projects in the Himalayas.
- A 2022 study indicates potential threats to over 650 planned or under-construction hydropower projects.
- These projects are located near glaciers or in areas prone to lake bursts.
- Many of these new projects are situated uphill from existing ones and close to glaciers and glacial lakes.
- The Northeast is crucial in the hydropower strategy of successive central governments.
- The Chungthang Dam is part of the 1200 MW Teesta Stage 3 Hydroelectric Project.
- The government asserts that these projects are environmentally friendly due to their low emission levels.
- Hydroelectric power is a significant revenue source for Sikkim.
- However, ecologists warn about the negative impact of dam construction as it destabilises rocks in the Himalayan region.
- The recent calamity serves as a reminder to consider these warnings and implement robust safety measures.