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An overwhelming flash flood has wreaked havoc upon Sikkim, leaving behind a path of devastation. This calamity was set in motion by a Glacial Lake Outburst Flood (GLOF), a dangerous outcome of climate change-induced glacier retreat.
Recent satellite imagery, made public by the Indian Space Research Organisation (ISRO), has provided crucial insights into the sequence of events preceding the Sikkim flood. These images unveiled the chain of events whereby an avalanche, potentially instigated by climate-related changes, instigated the outburst of Lhonak Lake in northern Sikkim.
The above map shows the condition of South Lhonak Lake and its surroundings as captured by RISAT 1A on October 4, 2023, at 0600 hrs.
The following map shows a comparison of South Lhonak Lake before and after the event, with observations from RISAT 1A on October 4, 2023, at 0600 hrs, and Sentinel 1A on September 28, 2023, at 1800 hrs.
The next map shows the temporal changes in the lake’s area on September 17, 2023, September 28, 2023, and October 4, 2023.
The ISRO website further states that it is evident that the lake has experienced a breach, resulting in the drainage of approximately 105 hectares of its area (as observed between the images taken on September 28, 2023, and October 4, 2023). This breach is believed to have contributed to a flash flood downstream.
This catastrophic occurrence then acted as the catalyst for a flash flood in the Himalayan state, resulting in the loss of lives and the sweeping away of critical infrastructure, encompassing roads, bridges, and dams.
Regarding Lhonak Lake, scientists have long considered it a disaster waiting to happen.
In 2019, a report prepared by the Sikkim State Disaster Management Authority highlighted findings from 2013 when scientists K. Babu Govindha Raj, S. N. Remya and K. Vinod Kumar at the National Remote Sensing Centre in Hyderabad had already identified Lhonak Lake as being at “significant risk” of experiencing a Glacial Lake Outburst Flood (GLOF). Such an event was deemed capable of inflicting extensive harm to both human lives and property in the downstream regions. The study revealed a high probability of a lake outburst, estimating a peak discharge of 586 cubic meters per second (m³/s).
The study further disclosed a concerning expansion of South Lhonak Lake’s area over the years, growing from 17.54 hectares in 1977 to 37.3 hectares in 1989, 78.95 hectares in 2002, and a worrisome 98.73 hectares in 2008.
The Sikkim State Disaster Management Authority (SSDMA)’s report emphasized Lhonak Lake’s extreme vulnerability to a glacial lake outburst flood, an event with the potential to wreak extensive havoc on life and property downstream. The report sounded the alarm regarding the risk of “flash floods,” specifically mentioning that crucial infrastructure, such as dams and powerhouses, remained susceptible to damage.
It also pointed out that townships like Chungthang, Dikchu, Singtam, and Rangpo were at risk, with the likelihood of significant loss of life and property.
Miriam Jackson, a senior specialist in cryosphere studies at the International Centre for Integrated Mountain Development, based in Nepal, has stated that the rise in such extreme events has become more frequent “due to the ongoing warming of the climate, pushing us into uncharted territory.”
The Impact on Sikkim
A statement from the Sikkim government cited severe damage in districts such as Mangan, Gangtok, Pakyong, and Namchi. The calamity led to the destruction of the Teesta-III dam at Chunthang, along with damage to sections of Teesta-5. Additionally, officials reported the loss of at least 14 bridges and significant damage to National Highway 10 (NH10) in multiple areas.
The sudden deluge submerged villages and towns, resulting in the destruction of residences and the displacement of numerous residents. Rescue and relief operations were hit as essential infrastructure like roads and bridges was washed away. Moreover, the floodwaters contaminated sources of drinking water, giving rise to a public health emergency.
Sikkim’s distinctive environment and diverse biodiversity will also face significant adversity. Delicate ecosystems, housing endangered species, are enduring the brunt of the catastrophe. The flood exacerbated existing ecological issues in the area, emphasizing the urgency of conservation efforts and sustainable practices. Furthermore, the disaster underscored the susceptibility of Sikkim’s infrastructure to the impacts of a shifting climate.
In the wake of this tragedy, Sikkim’s Chief Minister, Prem Singh Tamang, implored the residents of the state to remain vigilant. He acknowledged the severity of the natural disaster and detailed the mobilization of emergency services to the affected areas.
Understanding GLOFs: The Science
Glacial Lake Outburst Floods (GLOFs) are caused by the sudden breach of glacial lake dams, often formed as glaciers melt and recede. These lakes become increasingly hazardous as they grow larger and are blocked by ice or sediment, creating unstable natural dams. When these dams break, enormous volumes of water rush downhill at astonishing speeds, causing devastating floods in downstream areas.
GLOFs can be triggered by various factors, including earthquakes, heavy rainfall, or ice avalanches.
How Climate Change leads to Glacial Lake Outburst Floods (GLOFs)
Glacial Lake Outburst Floods (GLOFs) represent a harrowing consequence of climate change, accentuating the perilous transformations occurring in our world’s cryosphere—the frozen realms of glaciers and ice-covered lakes. As global temperatures surge, glaciers are receding at an alarming rate, causing the formation of large glacial lakes nestled behind unstable natural dams of ice and debris. This precarious situation sets the stage for GLOFs, where a breach in these dams unleashes colossal torrents of water and debris down mountainsides, resulting in catastrophic floods in downstream areas.
Climate change plays a pivotal role in exacerbating the GLOF risk. Rising temperatures intensify glacial melt, causing these lakes to grow larger and more vulnerable. The resulting floods pose severe threats to both human communities and ecosystems. Lives are lost, infrastructure is destroyed, and vital resources are compromised.
As global temperatures continue to increase and ice melts, the occurrence of violent flooding from glacier lakes restrained by unstable rock barriers has grown more frequent. The Sikkim flood stemming from a Glacial Lake Outburst Flood, serves as a poignant illustration of the consequences of climate change on vulnerable regions. This tragedy underscores the need for proactive measures, sustainable development practices, and global efforts to combat climate change—a collective endeavor that is vital to averting future catastrophes in this breathtaking yet vulnerable part of the world.
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References:
https://www.isro.gov.in/Satellite_studies_South_Lhonak_Lake.html
https://www.jstor.org/stable/24089638
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