India issues flood advisory for West Bengal and Assam after Bhutan's Shintaphu glacial lake outburst

A glacial lake outburst flood (GLOF) at Shintaphu Lake in Bhutan has raised concerns over a sudden surge of water flowing downstream into India, prompting the Government of India to issue a special advisory for parts of West Bengal and Assam, warning that water levels could rise sharply along the Sankosh River.

The outburst was reported on Thursday (Oct 29) evening at Shintaphu Lake, located below Wakila Mountain in Lungo, Laya Gewog, in Bhutan's Gasa district. Sirens were sounded to alert people living near riverbanks, while residents in the affected area were reportedly moved to safer ground.

Besides Assam's Dhubri district, alerts have been issued across parts of North Bengal, including the Darjeeling hills and Alipurduar, Jalpaiguri and Cooch Behar districts.

Shintaphu Lake is among Bhutan's 17 potentially dangerous glacial lakes. An official from the National Centre for Hydrology and Meteorology (NCHM) said a water-level monitoring station was located at Taktsimakhang, but no alert had been triggered there at the time of the initial reports. The extent of the outburst and its downstream impact remained unclear.

What is a glacial lake outburst flood?

A GLOF occurs when water stored in a lake formed by melting glaciers is suddenly released, often after a natural barrier fails or is breached. The resulting surge can travel rapidly through mountain valleys, carrying debris and damaging settlements, roads, bridges and farmland.

Shintaphu Lake lies within Bhutan's Punatsangchhu River basin. The river is known as the Sankosh after it enters India, making a sudden release of water a potential concern for downstream communities.

India issues special flood advisory

In response to the situation, India has warned that a flash flood in the upper reaches of the Punatsangchhu River could trigger a sudden rise in water levels in Alipurduar district of West Bengal and Dhubri district of Assam.

Authorities have issued alerts across parts of North Bengal, including the Darjeeling hills, Alipurduar, Jalpaiguri and Cooch Behar districts. NDRF and SDRF teams have been deployed in Tufanganj and Boxirhat in West Bengal's Cooch Behar district, along the Sankosh River near the Assam border, while residents are being alerted about the potential threat.

Meanwhile, BJP MP from Darjeeling, Raju Bista, also issued a critical public safety alert for residents living along the Sankosh River. In a post on X, Bista wrote, "A glacial lake outburst flood (GLOF) has been reported at Lemthang in Bhutan. The overflowing water from the lake is flowing downwards through the Mofu River towards the Sunkosh River. Therefore, everyone living in the catchment areas of the Sunkosh River and all its connected tributaries have been informed to move to a safe distance immediately to protect their lives."

According to the advisory, floodwater was expected to reach the India-Bhutan border within six to eight hours. Authorities in both districts have been urged to closely monitor the situation and take necessary precautionary measures.

West Bengal minister urges evacuation

West Bengal Forest Minister and Kumargram MLA Manoj Kumar Oraon urged residents living along the Sankosh River in Alipurduar district to move to safer locations.

In a video message posted on Facebook, Oraon warned that a surge of water could reach the river in Kumargram within the next one to one-and-a-half hours. He appealed to residents to evacuate as a precaution and cooperate with the administration.

"Everyone in our Darjeeling hills, Terai and Dooars region are requested to stay alert," he also added.

The Sankosh flows from Bhutan into India and supports communities across parts of northern West Bengal and adjoining Assam. A sudden rise in its water level could threaten riverside settlements, livestock, farmland and infrastructure. Authorities are monitoring the situation as they assess the movement of floodwater and the potential risk to downstream communities.

A history of devastating GLOFs

In October 1994, Bhutan witnessed one of the most devastating Glacial Lake Outburst Flood (GLOF) disasters along the Punatsang Chhu Valley, Punakha. The partial outburst or collapse of the moraine dam at Lugge Tsho (Luggye Lake), located in the Lunana region of Gasa Dzongkhag, triggered the flood. Roughly 18 million cubic meters (about 18 billion litres) of water rushed down into the river system, cascading down the Pho Chhu and Punatsangchhu valleys, travelling about 100 kilometres to reach Punakha in under five hours.
At least 21 people were killed in the surge that swept away homes, livestock (yaks and cattle) and extensive agricultural land. The historic Punakha Dzong fortress also suffered severe structural damage when the floodwaters undermined its perimeter walls.