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Updated: Jan 22, 2019 08:37 IST

Chaturangi glacier, a tributary of the Gangotri glacier, is retreating at a “considerable rate” and may vanish in the future, according to a research paper accepted to be published in the Current Science journal’s February edition.

The retreating glacier is another example of the impact of climate change and, according to one of the study’s contributors, affects water flow in the Ganga, which is fed by the Gangotri.

The study by scientists from GB Pant National Institute of Himalayan Environment and Sustainable Development and the Centre for Earth Sciences at the Indian Institute of Science (IISc) uses satellite data from 1989 to 2016 and kinematic GPS (a satellite navigation technique used to enhance precision of data from satellite-based positioning systems such as global positioning system, or GPS) to arrive at the retreating rate of Chaturangi glacier.

The Chaturangi glacier was connected with the Gangotri glacier till 1989 but is now detached and retreating at the rate of about 22.84 m/year, according to the study.

According to the paper, a similar pattern of retreat has also been reported from a previous study on the Gangotri published in 2008. But the retreating rate of Gangotri is far slower than that of the Chaturangi glacier.

“In 2017, we calculated the retreating rate of Gangotri glacier but the research is yet to be published. The overall health of the Gangotri glacier is not worrying because the retreating rate is about 9 to 12 m/year, less than its tributary glaciers and other glaciers like Dokriani in Uttarkashi in the same latitude and altitude,” said Harish Bisht, junior research fellow at Kumaun University and senior author of the Current Science paper.

He added that there is consensus among researchers and scientists that the majority of glaciers in Uttarakhand Himalayas are retreating.

“The variability in retreating rate is not only controlled by climate change but is also governed by glacier size, type, topographic setting and debris cover. The retreating rate of the Chaturangi glacier is higher than the Gangotri glacier because of its smaller size and fast response time to climatic variability,” reads the paper.

That may have an impact on the Ganga.

“Gangotri has many tributary glaciers but the Chaturangi and Raktavaran glaciers are two tributary glaciers retreating at a worrying rate. They may disappear in the future. The larger glaciers in the Himalayas are retreating at a relatively slow rate. Since Ganga originates from Gangotri glacier, which is fed by tributary glaciers, the rapid retreat of glaciers like Chaturangi and Raktavaran will definitely impact flow and water level in the Ganga,” said Prakash Chandra Arya, an IISc researcher who contributed to the study.

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According to NASA’s Land Use Land Cover Change programme, glacial melt will “in the long run... water supplies in those regions [Himalayas rivers] will be in peril”. There will also be an impact to agriculture, including soil loss due to soil erosion, landslides and floods, and temperature increase in areas downstream.

Indian Space Research Organisation (ISRO) has been mapping the long-term health of Himalayan glaciers. ISRO’s web mapping service on Bhuvan says information on glaciers (retreat/ advance) in the 13 sub-basins of Himalaya has been generated using satellite images of 1989-1990 to 1997-2008 time frames under the “Snow and Glacier Studies Phase-I”. Of 2,190 glaciers, about 76% have shown loss in area of ice cover and about 24% glaciers either did not show any change or showed gain in area. More recent data on glaciers is yet to be released, said an ISRO scientist.

“If smaller glaciers are retreating at a considerable rate, it will have a feedback effect downstream. Water volume in Ganga could reduce because the glacier is moving away from the source. Glacial lakes may also form due to accumulation of melt water but I don’t know of any comprehensive study on how river flow has been affected by glacial retreat in the Himalayas,” said Abhijit Mukherjee, associate professor (hydrogeology), department of geology and geophysics at IIT Kharagpur.

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Bisht and other researchers are currently carrying out a vulnerability assessment of the Glacial Lake Outburst Flood (GLOF) in Uttarakhand Himalayas.

“We have noticed formation of glacial lakes around the Gangotri glacier which also often contributes to glacial retreat by dissolving ice. It also increases the risk of GLOF disasters,” Bisht added.