Is climate change the reason for Sikkim flash floods?

On October 4, India woke up to the disturbing news of 23 Army personnel missing due to a flash flood that occurred at 1.30 am in the Teesta River in Lachen Valley after a sudden cloudburst in north Sikkim. Within a few hours, the state chief secretary said that around 15,000 people were affected, and at least 8 major bridges along the Teesta had got washed away. The main highway connecting Sikkim and West Bengal collapsed and Gangtok got totally cut off by road. The flood submerged several towns in the hilly state, including Dikchu, Singtam and Rangpo located in the Teesta basin. Many Army camps and vehicles were submerged.As of now, 82 bodies have been recovered and at least 100 are still missing. Among the Army personnel, only one has been rescued so far. Hopes of finding survivors among those reported missing may be fading, but rescue operations are still on.How did the devastating flash flood in Sikkim happen?Hours after the disaster struck, there were speculations about its reasons. But soon it was clear that the source of the water was the glacial lake South Lhonak, located in northwest Sikkim. It's a part of the glaciers that feed the Teesta River. A glacial lake is formed by the melting of the glacier.Usually when glaciers melt, its water flows down into the river channels. But there are many instances of obstructions to this water flow. This could be sediments of loose rock and debris called moraine. These form temporary dams which obstruct the water flow. When this happens, a lake forms close to the glacier. These are glacier lakes.Water keeps accumulating in these lakes, and a time comes when these temporary dams can no longer hold the water. There could be several triggers for this - earthquake, landslide, avalanche, or heavy rainfall.In Sikkim, heavy rainfall may have triggered the natural dam - South Lhonak Lake - to collapse. As a result, an overwhelming amount of water flowed down into the Teesta River basin and hit one of the largest hydro projects there - the Teesta Hydro Project. It led to further destruction downstream. One hazard led to another. This is called Cascading Hazard.Were there early warning signals of the flood threat in Sikkim?There were several warnings. The first warning came in 2001 when the Sikkim University studied South Lhonak Lake. Satellite pictures clearly show that in the past 30 years the lake had grown three times.Just two years ago, the Indian Institute of Science did a study which warned of an imminent glacial lake outburst flood (GLOF) due a breach in the Lhonak Lake.In 2016, members of the Sikkim State Disaster Management Authority and Sikkim's Department of Science and Technology and Climate Change together did a project to siphon off water from the lake. They pumped out water for a long time. But clearly, the efforts were not enough, and disaster struck.Has a similar havoc caused by glacial lake outburst flood (GLOF) happened in India in the past?Yes. The most well-known is that of the 2013 Kedarnath floods. The Chorabari Taal glacier situated north of the Kedarnath shrine burst. It caused massive devastation. We all know well the scale of destruction that it caused. Some 6,000 people died in the tragedy. That, too, was triggered by heavy rainfall in the upper reaches which made the temporary dams unstable, leading to the breach.In 2021, the Chamoli disaster happened. This was not really GLOF but was caused by a huge chunk of glacier falling into the river basin. Its impact was so huge that the snow instantly melted, and a large amount of water came down into the Dhauliganga river basin and into the Alaknanda River. Many lost their lives and the Tapovan dam site was destroyed.Does climate change play a role in increasing the threat of such extreme events?Climate change is exacerbating the risks. Because of global warming, more and more glaciers are melting. A Washington Post study said that in a 30-year period since 1990, glacial lakes worldwide have increased by 50 percent. Around 15 million people are at risk from GLOF. Of this, one third, that is around 5 million, live in India, Pakistan and the countries in the neighborhood of the Himalayas.The Himalayas hold a lot of water in the form of glaciers. There are many studies that give the number of glacier lakes here. One study puts it at 5,000. Another said that only the Hindu Kush, Karakoram and the western Himalayan region contain around 2,500 glacial lakes, of which 52 are potentially dangerous.In Sikkim, the number of potentially dangerous GOLFs was put at 14, of which the South Lhonak Glacier was seen as one that carried the maximum threat.Climate change is at the center of the threat.What can be done to minimise the damage to life and infrastructure in the mountains?First, we must understand that the mountains are ecologically and geologically fragile. There cannot be business-as-usual development in the Himalayas anymore. We must recognize the growing threats from climate change in the region.As far as glacial lakes are concerned, there are many ways to reduce its volumes. It could be done by controlled breaching or construction of outlets that would let water out. This was done in South Lhonak glacier. In 2016, Bhutan invested money to reduce water levels in its most dangerous glacial lakes. Such efforts can help mitigate threats from GLOF.Another way is to look at the risks in the areas and the infrastructure exposed to GLOF in the river valleys. Remove settlements that are at potential danger of such floods.We must be careful in granting permission for the design of our mega hydro projects. We must do proper environment assessment of these projects and ensure that these withstand any water discharge that may happen in case of a glacier outburst.Photo: PTIAudio production: Shantanu Nanoti