The Teesta basin within the Sikkim Himalaya is dwelling to a number of glacial lakes within the high-altitude, glacier-covered terrain. Among them, South Lhonak Lake stands out as one of the most important and fastest-growing.
Although these lakes are primarily located in distant and uninhabited mountain valleys, the results of glacial lake outburst floods (GLOFs) can lengthen over tens of kilometres downstream, leading to loss of human life and vital harm to property and infrastructure. A GLOF happens when the weak, unstable pure moraine that holds a glacial lake fails can not maintain the water within the glacial lake. Events like earthquakes, cloudbursts, and avalanches can set off a GLOF by breaking the moraine.
A latest cloudburst above South Lhonak Lake brought about it to breach its embankment, dumping the water into a channel that brought about the water within the Chungthang dam reservoir to overflow in addition to the reservoir itself to undergo harm. All this then triggered abrupt and devastating flash floods in several components of the hilly state of Sikkim.
Not simply excessive climate
Meteorologists have pressured that whereas current climate circumstances had been certainly beneficial for heavy to extraordinarily heavy rainfall, since a low-pressure atmospheric system was close by, the flash floods can’t be solely attributed to the singular occasion of excessive climate. Climate change has performed a huge half in altering the frequency and amplifying the depth of such climate phenomena – and human actions on unstable terrain have made their results extra devastating.
“We all know that in a warming world, the potential for cloudbursts, extreme rains, and GLOF has gone up,” Roxy Mathew Koll, a local weather scientist on the Indian Institute of Tropical Meteorology, Pune. “Ocean warming has already increased moisture levels over the region. The low-pressure area near the region further increased the moisture, [providing] a conducive environment for torrential rains.”
An anticipated catastrophe
As it occurs, scientists had anticipated the Sikkim catastrophe as early as 2021, when, in a examine revealed within the journal Geomorphology, they highlighted the increasing dimensions of the Lhonak glacial lake, which rendered a GLOF extra probably as a result of cloudbursts.
“There has been a substantial increase in the number of glacial lakes as the glaciers are melting due to global warming,” Farooq Azam, a glaciologist on the Indian Institute of Technology, Indore, mentioned. “When the glaciers advance, they erode the river bed, leading to the deepening of the river. Also, climate change has resulted in erratic precipitation, including events like cloudbursts, as we saw in Sikkim, leading to the partial breach of the moraine dam.”
Dr. Azam added that eroding glaciers apply strain on the bedrock, which then produces extra silt: “Whenever there is a flash flood, you will witness more silt and debris flowing downhill, aggravating the destruction caused by floods and landslides.”
‘Critical’ lakes
Glaciers within the space are melting and retreating, which has led to the accelerated progress within the quantity and measurement of proglacial lakes (i.e. lakes rising in entrance of the glaciers). And because the glaciers proceed to recede, the growth of these lakes can be linked to the topography of the uncovered mattress. For instance, if the mattress comprises a melancholy that turns into uncovered, water can gather there and ‘expand’ the lake.
As the lakes grow to be greater, the possibilities of a GLOF enhance as effectively.
The 2021 examine additionally singled 12 lakes out as ‘critical’ and 93 as ‘potentially critical’, out of 251 glacial lakes bigger than 0.01 sq. km. The criticality referred to the chance of a lake creating an outburst adopted by “potential downstream exposure”.
In one other related examine, revealed in May 2022, researchers from the National Institute of Technology, Rourkela, evaluated the potential downstream influence of 329 lakes throughout the Indian Himalaya, and located that 36 had been uncovered to potential avalanche-impact zones. This examine additionally recognized South Lhonak Lake as doubtlessly harmful, with a excessive outburst chance. In the final 29 years, the size of the glacier subsequent to which the lake is rising decreased from 6.4 km to five.1 km even because the water-body grew from 0.42 sq. km in 1990 to 1.35 sq. kmin 2019.
Rainfall and earthquakes
“Eastern Himalayas are dominated by the monsoon, which has over the period become more erratic and unpredictable,” Dr. Azam mentioned. “Snowfall is food for glaciers, but it is now replaced by rainfall, that too erratic. There are more days of heavy rain and [the number of] dry periods is also increasing. Rise in global warming has led to rise in glacial melt.”
Geologists have discovered that as glaciers recede, they deposit massive portions of sediment – composed of an unstable mixture of soil and rocks – within the higher areas of the Himalaya. In these circumstances, even a small quantity of rainfall can dislodge boulders and particles and go away them to stream downstream. As a end result, scientists deemed within the May 2022 paper the higher Himalayan area to be extremely unsuitable for the development of dams and tunnels.
Another risk like rain is seismic exercise: earthquakes can deteriorate the structural stability of the moraines. They could not essentially lead to outburst floods however they might nonetheless set off vital ice and/or rock avalanches. And this risk is price listening to as a result of South Lhonak Lake is situated in an space characterised by a excessive degree of seismic exercise. According to the National Institute of Disaster Management, Sikkim straddles land categorised as seismic zones IV and V – i.e. having the very best degree of seismicity.
Several earthquakes previously have additionally had their epicentres near the lake.
Landscape of uncertainties
“[We] don’t have high-resolution monitoring systems that could tell us what happened, how it happened, and to what extent climate change aggravated the scenario,” Dr. Koll mentioned in regards to the Sikkim GLOF. “We know the Himalayan region is prone to cloudbursts, but we cannot identify a hotspot. Thus, a proper monitoring network is the need of the hour.”
Scientists have additionally articulated the necessity for extra analysis to higher perceive the realm’s local weather sensitivity. There are greater than 54,000 glaciers throughout the Hindu Kush Himalaya however solely a few are literally monitored – 1-5%, in keeping with Anjal Prakash, director of the Bharti Institute of Public Policy, Indian School of Business, Hyderabad, and a coauthor of evaluation reviews ready by the Intergovernmental Panel on Climate Change.
On the opposite hand, building actions within the Himalayan area – particularly hydroelectric energy era amenities – should be moderated towards the uncertainty over how the mountainous system will reply.
“The location, size, and scale of these projects, the knowledge and experience of the developers, the capability of project-regulating agencies, and the way projects have been designed, and the technology used have been questioned all across the fragile Himalayan ecology,” improvement economist Mahendra Lama mentioned.
“Unfortunately, in many cases, these issues come up for public discussion only in the aftermath of disasters.”
