Eastern Himalayan Glaciers See Marked Retreat

New research sheds light on the impacts of climate change on glaciers in the Eastern Himalayan state of Arunachal Pradesh, where rugged terrains have made such inventories challenging in the past.

The Eastern Himalayan glaciers are distinct from their Western Himalayan counterparts on account of their low altitude and different “feeding mechanisms,” or when they accumulate snow. “Unlike glaciers in the Western Himalayas, the glaciers in the Eastern Himalayas are fed by both winter and summer precipitation. They’re generally wetter and smaller,” explained A.P. Dimri, Professor of Environmental Sciences at Jawaharlal Nehru University.

These characteristics can make these glaciers particularly sensitive to changes in weather patterns and temperature. The paper by researchers from Nagaland University and Cotton University in Assam found that smaller glaciers in the state were rapidly retreating, increasing the risk of forming hazardous glacial lakes.

Marked retreat in glaciers

Arunachal Pradesh is 83,000 square kilometres in size, and glaciers are found in elevations ranging from 3,000 to 7,000 metres. The study identified glaciers in the Tawang, West Kameng, Kurung Kumey, Upper Siang, Upper Dibang Valley and Lohit districts.

A majority of glaciers in the state are observed at an elevation of around 4,000 to 4,800 metres. “These are glaciers that have a high altitude, but a lower latitude,” said Nabajit Hazarika, co-author of the study and an Assistant Professor in the Department of Environmental Biology and Wildlife Sciences at Cotton University, Assam. “Temperatures are normally higher in these regions in comparison to the higher latitude areas. Even a small increase in warming can have a significant impact on these glaciers.”

The study found that between 1988 and 2022, the number of glaciers fluctuated widely. In 1988, the observed number of glaciers was 756, decreasing to 708 in 1995, 699 glaciers in 2000, and then increasing to 726 in 2005. Subsequent years showed fluctuations too, with 697 observed glaciers in 2010, 714 in 2015, and 646 in 2022.

Behind these fluctuations is the steady retreat of glaciers in Arunachal Pradesh, the study says. “As glaciers retreat, particularly larger ones, they have a tendency to break into two or more fragmented forms,” explained Hazarika.

While these glaciers stood over an area of over 585 square kilometres in 1988, they decreased to around 275 square kilometres in 2020. “The overall annual rate of area change for the glaciers was observed at 16.94 square kilometres per year during the entire study period (1988–2020). Glacial retreat has led to exposure of the bedrock of a glacier in Northern Arunachal Pradesh,” the study says.

Growth of glacial lakes

The study was able to capture these changes using 51 satellite images. Inventorising glaciers is useful for studying their changes over time, said Dimri. “Recording a reduction in glaciers is not unusual, but tracking these changes over time can help indicate the impacts of climate change and other anthropogenic pressures,” he said.

Another study that conducted a similar exercise on glaciers also looked at the formation of glacier lakes – lakes that result from glacier melt – in the Mago River Basin, Subansiri River Basin, and Dibang River Basin. This 2023 study by researchers from North Eastern Regional Institute of Science and Technology (NERIST) in Itanagar, similarly found evidence of glacial retreat across all three basins.

This retreat corresponds with an increase in glacial lakes across the study areas. Between 1995 and 2020, glacial lakes in the Dibang Basin grew from 20 to 22 (covering 3.1 square kilometres). In the Mago basin, glacial lakes increased from 15 in 1988 to 25 lakes in 2017, covering an area of 2.11 square kilometres, while in the Subansiri Basin, the number of glacial lakes increased from four in 2013 to five in 2022 (covering 0.85 square kilometres).

“The Dibang Basin consists of the highest number of glacier lakes due to its relatively lower elevation compared to the other two basins,” the study says, adding, “These fluctuations will impact the pace of lake expansion and the likelihood of outburst events in each of the sub-regions in the future.”

Arnab Bandyopadhyay, a co-author of the paper and an assistant professor in the Department of Agricultural Engineering at NERIST, said this research would lend itself well to analysing GLOF susceptibility in the state. In 2023, a GLOF caused widespread damage in the state of Sikkim. “Satellite imagery has made it possible to create an inventory of glaciers in places where ground truthing is nearly impossible. Having an accurate inventory can help accurately model water basins too,” he said.

(Published under Creative Commons from Mongabay-India. Read the original article here)