By C.P. Rajendran

The disaster that struck Sikkim in the early hours of Wednesday, October 4, ended up killing at least 40 people and many more are reported to be missing, according to currently available reports. The surge of floodwaters flowing into the Teesta River in Lachen Valley was so intense that it washed away several bridges and roads and it rammed the biggest hydroelectric project, the Teesta-III Dam in Chungthang in Sikkim, causing part of it to give away. According to a statement issued by the National Disaster Management Authority, the flash flood was the result of a cloudburst causing the Lhonak glacial lake, located at 5,200 metres above sea level, to overflow the impounding moraine, eventually eroding it to form an outlet.
A glacial lake outburst flood, or as it is known in scientific literature by the acronym GLOF, usually results in more damage and destruction than a flood caused by excess rainfall alone. It is worth remembering that on February 7, 2021, a similar catastrophic mass flow descended the Rishiganga and Dhauliganga Valleys in Chamoli, Uttarakhand, killing more than 200 people and damaging two hydropower projects. The 2013 Kedarnath disaster was another devastating example of GLOF caused by the overflowing glacial lake up in the mountain, resulting in 6,000 fatalities.
The Sikkim disaster appears to be a repeat of events like the one that happened at Kedarnath in 2013 and Chamoli in 2021 – a sequence of events that marks the increasing risk caused by the upward trend in global warming and sustained melting of mountain glaciers. Combined with unregulated constructions, hydroelectric projects and anthropogenic activities, these events evolve into massive disasters.
The Geological Survey of India reports about 9,575 glaciers in the Indian part of the Himalayas. The annual rate of retreat of glaciers in this part ranges between 5 and 20 m per year. Based on satellite-based observations, it is estimated that the Himalayas lost 13% of the glacier area between 1960 and 2000; that is about 0.3% per year. Himalayan glaciers are losing mass at the rate of 6.6±1 Gt per annum, which is nearly 0.2% per year.
I met a Buddhist monk in the far-eastern part of Bhutan – a country landlocked in the Eastern Himalayas. Trekking alongside him in the mountains there in 2014, he showed a group of us the glaciated mountains in the distance and told us that the glaciers were indeed retreating. He has been closely watching these changes since his childhood, and this, I consider a credible personal report from the field.
In a study published in the journal Science Advances in June 2019, around 650 glaciers across India, China, Nepal and Bhutan show confirmed signs of retreat. The study identifies global warming as the cause of the melting and loss of glacial ice over a large area confirming the role of global warming. The studies also indicate that the average temperature in the Himalayas has risen by 0.66° C since 1991 – an increase much higher than the global average. The higher Himalayas became even warmer on average in the same period. The winters in the Himalayas have been getting warmer and wetter over the last 25 years. The unprecedented extreme rainfall events as seen in Himachal Pradesh during this year’s monsoon season are attributable to climate shifts.
The studies published in 2019 in PNAS show that the sustained glacier melt has produced more than 5,000 glacier lakes in the Himalayas, dammed by potentially unstable moraines – the loose debris transported by glaciers. These lakes are prone to outbursts triggered by ice or debris falls, earthquake shaking or overtopping waves generated by intense rainfall. The erosion of impounding barriers takes place within minutes or hours, releasing sediment-laden water rushing downstream, and destroying everything in its wake. The studies also indicate that glacier lakes are much larger in number and have occurred in clusters in the Central and Eastern Himalayas since 1990, compared to the other parts of the mountain range.
The analyses of satellite-borne remote sensing data carried out in 2013 by the Centre for Development of Advanced Computing in Pune jointly with the Sikkim State Council of Science and Technology had shown that many glacial lakes in Sikkim Himalaya have expanded their spatial extent, accompanied by the retreat of glaciers from 1965 to 2010. The expansion of Lhonak and South Lhonak glacial lakes in an interval of 45 years was also found to be significant and both have been flagged as potential GLOF sources.
The Sikkim event was forecast by later studies too, led by the researchers in the Divecha Centre for Climate Change, Indian Institute of Science. The paper of December 2021 in the journal Geomorphology discusses the outburst potential of South Lhonak glacial lake in detail. The studies highlight that the length of the glacier that is feeding the lake over the last 29 years has been reduced from 6.4 k to 5.1 km, while the overall glacier shrank by 0.96 sq km. In line with the glacier retreat, the lake has been exhibiting significant growth over the years as it grew from 0.42 sq kmin 1990 to 1.35 sq km in 2019. This is a substantial growth in its area, registered by the lake.

What can be done?
The Sikkim disaster shows that repeated warnings from the individual research groups that have been communicated through scientific reports and papers in the past were ignored and the contingency plans were put on the back burner. The written replies from the national agencies on potentially dangerous glacial lakes that were published in the 23rd report of March 2023, submitted by the Parliamentary Committee, do not mention the potentially hazardous ones located in the Sikkim Himalaya.
Why was a highly expensive hydroelectric project costing about Rs 14,000 crore, commissioned only in 2017, which was breached and severely damaged in the flood, not taking the flood projections into account? Who is accountable for the under-engineered structure? The Union and state governments are hand in glove in building up dams in the Himalayan states to tap the hydroelectric power. The Teesta dam mishap is yet another warning to reconsider the efficacy and sustainability of such projects constructed within the dynamic environmental settings of the Himalayas.
The Parliamentary Committee had raised the issue of the “severe shortage of meteorological and monitoring stations in Himalayan regions”, in its report presented to the Lok Sabha on March 29, 2023.

C.P. Rajendran is an adjunct professor at the National Institute of Advanced Studies, Bengaluru and a director of the Consortium for Sustainable Development, Connecticut, the US.

Courtesy: The Science Wire