Glacier retreat in Arunachal's Mago Chu basin poses flood risk: Study

A new study has found evidence of rapid glacier retreat, expanding high-altitude lakes and enhancing flood risk in the Mago Chu sub-basin of western Arunachal Pradesh, one of the most ecologically significant headwater zones of the Brahmaputra river, a scientist said.

It shows that the glaciers of the basin have lost nearly 28.5 per cent of their area between 1988 and 2019, equivalent to more than 15 square kilometres of ice.

The research was carried out by the Centre for Earth Sciences and Himalayan Studies (CESHS) here in collaboration with the National Centre for Polar and Ocean Research (NCPOR), IIT Roorkee, IIT Guwahati and other partner institutions.

Larger glaciers have fragmented into smaller ones, particularly on the south-west facing slopes, where ice loss has reached almost 50 per cent, the study said.

The Equilibrium Line Altitude (ELA), a critical indicator of glacier health, has risen by about 137 metres in the same period, confirming that the glaciers are not being replenished and remain in a state of negative mass balance, the researchers found.

“Glaciers in the Mago Chu are retreating faster than many parts of the Western Himalaya. What is more concerning is that large glaciers are breaking down into smaller and unstable fragments that are more vulnerable to melt and collapse,” said Centre for Earth Sciences and Himalayan Studies (CESHS) Director Tana Tage said.

The glacial retreat is not only a warning for Arunachal Pradesh but for the entire Brahmaputra basin across India, Bhutan and Bangladesh, he said.

"Strengthening our scientific capacity, engineering solutions, and community resilience is the only way forward to safeguard both local heritage and downstream livelihoods,” the director added.

He noted that the Mago Chu basin is "dominated by summer-accumulating glaciers, dependent on the monsoon for replenishment, but rainfall in the region has declined drastically.

“Monsoon precipitation has fallen sharply from about 2,100 millimetres in the mid-1980s to less than 1,500 millimetres after 2000, and in 2024, we recorded barely 900 millimetres. With winter snowfall almost absent, these glaciers are losing their natural recharge system,” the director said.

The decline in ice cover has been accompanied by a dramatic growth in glacial lakes. In 1988, the basin had 15 lakes covering 0.71 sq km.

By 2017, the number had nearly doubled to 29, with a combined area of 2.11 sq km. Four of these lakes are listed among the National Disaster Management Authority's ‘high-risk' sites in the state, he said.

“We are now dealing with lakes that did not even exist a few decades ago. Some have grown from tiny depressions into reservoirs larger than 0.8 sq km. Without detailed bathymetry and moraine stability studies, it is difficult to say when or how these lakes might breach,” Tage cautioned.

Recent field investigations have confirmed the pace of change.

CESHS researchers recorded nearly one metre of ice loss on Khangri Glacier during the last winter season with negligible snow accumulation, pointing to strong melt acceleration.

An automatic weather station and automatic water level recorder now provide real-time observations on climate and hydrology, the first such continuous data from this remote frontier, he said.

“For the first time, we are able to study glacier–climate interactions in real time in one of the easternmost high-altitude basins of the Himalaya. These observations validate what remote sensing has long indicated, that the glaciers are losing mass rapidly,” he said.

The risks for downstream settlements are serious.

According to the scientist, hydrodynamic models suggest that a full breach of one of the high-risk glacial lakes could release flood waves exceeding 12,000 cubic metres per second, inundating villages such as Mago, Thingbu and Chagzum and threatening hydropower installations along the valley.

“Science alone cannot save lives. We need to integrate our data with community preparedness, evacuation drills and early warning systems. The people of Tawang and neighbouring valleys have lived with these landscapes for centuries, and their resilience and knowledge must be part of the solution,” Tage stressed.

Plans are also underway to establish a prefabricated permanent base camp in the state to support long-term cryosphere monitoring, he said.

According to the director, the Mago Chu basin is both a sentinel of global climate change and a testing ground for adaptation strategies.