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Climate change triggers deadly glacier lake outburst flood in Sikkim

A glacial lake outburst flood in Sikkim last week has left a trail of devastation, with over 40 people dead, many missing, countless injured.

By Wahid Bhat
New Update
Climate change triggers deadly glacier lake outburst flood in Sikkim

A glacial lake outburst flood (GLOF) in Sikkim last week has left a trail of devastation, with over 40 people dead, many missing, and countless injured. The flood was triggered by heavy rainfall, which scientists believe has been exacerbated by climate change.

Meteorologists state that the weather conditions in the area were utterly favourable for such heavy rainfall. They attribute this to the presence of a nearby low-pressure area. However, scientists assert that climate change has undoubtedly contributed to the severity of this rainfall.

Size of South Lhonak Lake increased

A study conducted in 2021 revealed that the size of South Lhonak Lake has increased seriously. The same study stated that the lake's vulnerability to extreme weather like heavy rains has increased. Since we cannot foresee when the glacier will flood, our only course of action is to prepare for any possible flood. We need to plan properly for disaster risk reduction and damage control.

Thangu Valley, Sikkim, India.

Dr. Farooq Azam, a glaciologist, explains that the number of glacier lakes has increased due to melting of glaciers due to global warming. As glaciers grow in size, they dig deeper into river beds. Additionally, climate change has created unpredictable conditions, such as last week's torrential rains in Sikkim. The lake overflowed. When the glaciers erode, they put more pressure on the bedrock. This creates more silt. Floods and landslides then carry more silt and debris downstream, increasing the destruction.

"The monsoon is more irregular and unpredictable in the eastern Himalayas. Snowfall nourishes the glaciers but now rains occur more frequently. Days of heavy rain and dry periods are increasing. Due to global warming the glaciers More melt,” says Dr Farooq Azam.

Although glacier lakes mostly occur in remote mountain valleys, their bursting can cause damage several kilometers downstream. Life, property, and infrastructure may be affected. We are currently seeing this in Sikkim.

South Lonak Glacier Melting threatens Sikkim Valley

The rapid melting of the South Lonak Glacier, which has retreated approximately 2 km from 1962 to 2008 and a further 400 meters from 2008 to 2019, is causing increasing concern about the danger of floods in the lake. The lake, now the largest and fastest-growing in Sikkim, is located in a valley with many settlements and infrastructure.

Before and after the Chungthang Hydroelectric Dam, North Sikkim. Photo Credit: X/Siddharth Agarwal

Heavy rainfall can cause flooding in the glacier, destroying the naturally formed moraine dam and filling the lake beyond its limits. Studies show that the risk of such glacier floods is likely to increase in the future due to more new lakes and their increased trigger capacity.

Melting glaciers also increase silt levels, leaving behind a lot of loose sediment – soil and rocks. Even a little rain can carry these stones and debris downstream. This makes the high Himalayan region unsuitable for dams and tunnels.

Earthquakes can also attack the integrity of a moraine dam. It is important to mention here that South Lhonak Lake is in a very seismically active area. Previous earthquakes had occurred nearby.

IPCC author warns of increasing climate threats

Anjal Prakash, one of the IPCC authors, warns, “The frequency and severity of such events will increase rapidly in the future. The Himalayan ecosystem is one of the most fragile in the world. Any disruption in the management of these resources will be problematic. Rising temperatures will lead to more severe events but also disturbs the delicate Himalayan ecosystem through dams. Flood outbreaks in glaciers are caused by regional warming. Once formed, we do not know what will cause the eruption. Sikkim is This is the latest example.”

Anjal Prakash further explains, “More research is crucial for a nuanced understanding of climate-sensitive areas. Very few of the more than 54,000 Himalayan glaciers are monitored. This lack of monitoring and absence of information means that disasters will continue to increase. Scientific monitoring should form the basis of policy decisions and is currently lacking."


Future looks dark

Snow, glaciers, and permafrost are projected to continue declining in most areas throughout this century. The Intergovernmental Panel on Climate Change (IPCC) predicts that the number and area of glacier lakes will increase in the coming decades. Experts expect new lakes to form near steep, unstable slopes where landslides could potentially trigger explosions.

The melting of snow and glaciers will further alter river flows, impacting agriculture, hydropower, and water quality in some regions.

This issue now calls for more precise scientific monitoring. Climate scientist Dr. Roxy Matthew Cole comments, "We know that the likelihood of extreme rainfall and floods has increased. Ocean warming elevates regional moisture levels. More moisture in low-pressure areas results in heavy rainfall. However, we lack the monitoring to accurately determine what happened and to what extent climate change was a factor. We know the Himalayas are prone to cloudbursts, but we haven’t identified hotspots. Therefore, proper monitoring is essential.”

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