Ishita Mishra | TNN | Updated: Feb 8, 2021, 08:32 IST
DEHRADUN: It’s winter. February temperatures can drop to below zero in the hills of Uttarakhand’s Chamoli and summer is a long way off. Why, then, did a glacier break off, with disastrous effect? Geologists who have been studying the region’s glaciers said climate change is to blame.
“This is an anomaly. In winter, glaciers remain firmly frozen. Even walls of glacial lakes are tightly bound. A flood of this sort in this season is usually caused by an avalanche or landslide. Neither seems to be the case here,” Manish Mehta, senior scientist at Wadia Institute of Himalayan Geology, told TOI. He could not immediately recall a precedent.
Mehta had led a study last year which found that the eight glaciers of the upper Rishiganga catchment – Uttari Nanda Devi, Changbang, Ramni Bank, Bethartoli, Trishul, Dakshni Nanda Devi, Dakshni Rishi Bank and Raunthi Bank – had lost over 10% of their mass in less than three decades. From 243 sq km in 1980, they had shrunk to 217 sq km in 2017, with Uttari Nanda Devi receding the most (7.7%). The upper Rishiganga catchment is where the glacier burst took place on Sunday.
In the same period, the equilibrium line altitude (the zone on a glacier where its mass lost is balanced by its mass gained over a year) fluctuated a lot – between 5,200m above sea level and 5,700m. “It does not change if climate conditions are consistent,” MPS Bisht, director of the Uttarakhand Space Application Centre, which was also part of the study along with IIT-Kanpur and HNB Garhwal University, said.
Himalayan glaciers have been retreating faster than anywhere else in the world. “Yet, the state of glacier response (how much it retreats or advances) has not been studied extensively. So, we mapped the variations of extent and dynamics of the glaciers in the upper Rishiganga catchment, Nanda Devi region and found most glaciers have been shrinking,” Mehta said.
This has been pronounced since the 1990s. “We found south-facing glaciers receded faster than north-facing ones, possibly because of longer exposure to insolation (solar radiation). How glaciers respond to climate is also dependent on its size and geometry.”
Because the glaciers are of the “winter accumulation type,” a decrease in precipitation may have caused this, the study said. “The equilibrium line altitude swing suggests glaciers in the region have responded to deprived precipitation conditions since 1980,” Bisht said. And while temperatures have been increasing since the 1980s, the study said, the glaciers are more sensitive to changes in precipitation. The larger context, however, is that of increased global temperatures. Mehta said, “Against the backdrop of warming since the mid-1990s, accelerated glacial reduction could be correlated with increased global temperature.”