New Delhi: A month after the disaster in Chamoli district in Uttarakhand, in which at least 70 persons died and 130 or so more remain missing, scientists from three premier institutions have analysed more data to determine the likely cause of the incident – including heavy snowfall just before the day of the disaster, an overall increase in ambient temperature in the area, a rock and ice avalanche at an altitude of 5,600 metres, and a large volume of meltwater and glacial moraine hurtling down a narrow gorge.
While the exact answer likely lies at the intersection of these possibilities, two things are clear: that climate change played a part and that governments should reconsider setting up hydroelectric projects in the higher Himalaya.
As rescue operations continue, the state government has declared 72 people dead and 133 missing as a result of the flash floods, which also wrecked two hydroelectric power projects: the National Thermal Power Corporation’s Tapovan-Vishnugad project and the Rishi Ganga Hydel Project.
Scientists from the Divecha Centre for Climate Change (DCCC) at the Indian Institute of Science, Bengaluru; a group called the Glacier and Permafrost Hazards in Mountains (GAPHAZ) and the International Centre for Integrated Mountain Development (ICIMOD) have reported that they were able to reconstruct the chain of events leading to the tragic event on February 7, based on satellite and other data.
The Chamoli disaster drew international attention because, among other reasons, it was clearly a symptom of climate change’s disproportionate impact on the Himalaya. Of the 40,000 or so sq. km over which these mountains spread – creating the third pole, the world’s largest repository of snow and ice outside the two poles – and encompass eight countries, India straddles about 23,000 sq. km. Taken together, this area represents a potential of 3,651 cubic metres of water crucial for almost 40% of its population, resident in the Indus, Ganga and Brahmaputra basins.
Using in-house models, the DCCC team estimated the run-off in the Rishi Ganga river’s catchment area, of 689.6 sq. km, including 69 glaciers over 176.1 sq. km. As much as 44.5% of the water here came from snow and glacial melt, 23.4% from rainwater and 32.1% from the base flow, the team estimated.
The scientists also calculated the ice volumes of six of the eight glaciers of the Nanda Devi massif that feeds the Rishi Ganga. Of them, North Nanda Devi has the largest ice volume, of 2.76 cubic km, followed by Trishul (1.76 cubic km), Rishi (1.17 cubic km), Betharholli (0.52 cubic km), Raunti (0.85 cubic km) and South Nanda Devi (0.50 cubic km). The ice volume of the near-vertical block that fell off the Raunti glacier ahead of the Chamoli disaster was estimated to be 6.86 million cubic metres – in line with the GAPHAZ team’s estimates as well.
The GAPHAZ group also observed that a major rock and ice avalanche detached itself at an elevation of about 5,600 m above sea level from a north-facing slope northeast of Trishul Peak, in the Nanda Devi mountain. The reason for this, the group’s members argue, could have been the result of a failure within the mountain’s bedrock and that the glacier ice become entrained with the collapsing block of bedrock. The group predicted that this mass could have set off the floods in the Rishi Ganga river.
“The failing mass covered an area of around 0.2 sq. km. Current estimates yield a total avalanche volume of 20 million cubic metres of rock (83%) and 4 million cubic metre of ice (17%). This puts the event into a category of the largest contemporary mass-movement in mountains at a global scale,” a press release from GAPHAZ claimed.
Following their own analysis, the results of which were released on March 5, scientists at ICIMOD, an intergovernmental agency, have said that the Chamoli disaster was not the result of a glacial lake outburst flood since there were no significant glacial lakes in the area. Instead, they considered heavy precipitation in the Chamoli region (58 mm during February 3-5), most of it in the form of snow, and the rise in average temperature in Uttarakhand in the last four decades (the maximum temperature in Chamoli had increased by 0.032º C per year between 1980 and 2018). They also noted that January 2021 had been the warmest January on record in Uttarakhand in six decades. Finally, the snow cover in the area dropped significantly between February 6 and 10.
“While a hazard event like the flood at Chamoli cannot be directly attributed to climatic changes, the increased thaw-freeze cycle of permafrost could have partially contributed to the event,” the authors observed.
The scarp left by the rockslide is 150 m deep, has a slope of 39º, is about 1,060 m long and covers some 350,000 sq. metres – yielding an approximate volume of 22 million cubic metres. “We estimate the fraction of rock to be 85% and ice 15%,” the ICIMOD authors said.
“From the 200- to 400-m-high surge of debris on the adjacent headwalls below, we can estimate the velocity of the fall. The debris flow took about 18 minutes to reach the Tapovan Hydropower Project site and was able to move [approximately] 1000 cubic metres per second of water, assuming only 75% of the energy from the rockslide was used to fluidise the deposited ice below. This would explain, to a large part, how such a strong flood wave was able to reach downstream areas without a previous body of water being present.”
This conclusion is in line with the findings of a four-member team from the G.B. Pant Institute of Himalayan Environment and Development, which had visited the area shortly after the disaster took place. Amar Ujala reported that this team had found that upstream of Reni village, where the gorge is very narrow, floodwaters had risen as high as 125 metres. The team also found the flood had had an impact all the way up to Karn Prayag, which is more than 100 km downstream from Reni.
What next?
There are 1,474 glaciers covering more than 10 sq. km in Uttarakhand, covering a glaciated area of 2,148 sq. km. An older DCCC study had established that these glaciers’ mass balance had declined by 7.3 billion tonnes, to 117 billion tonnes, between 2000 and 2013.
“Using our modelling, DCCC has been able to estimate that there are 63 glacial lakes spread over 842 hectares in the higher reaches of Uttarakhand, with 184 million cubic metres of water,” Anil Kulkarni, a distinguished visiting scientist, told The Wire Science. So “we can predict the expanse of existing lakes and also the potential spots where further lakes can develop.”
Given the damage to the two hydropower projects, all three studies also warn against erecting hydropower projects in the Himalaya’s higher reaches. “Mitigating the risk of climate change and flow variability is of paramount importance for future energy security for which a better understanding of future climate projections and water availability is needed,” the ICIMOD study said. “That understanding can be reflected in the design and location consideration of future hydropower projects in the region.”
The GAPHAZ study warned that recent, high-resolution images obtained by satellites indicate that the mass-movement of rock and ice continues in the same area. And “in case of another slope failure and avalanche, this can be critical for people and infrastructure downstream, close to the riverbed,” it said. “It can be a normal, follow-up activity of the main event but it cannot be excluded that important secondary events can occur.”
Meanwhile, the Uttarakhand government contends with several challenges. As rescue and relief operations continue at Chamoli and surrounding areas, it also confronts an impending breach at Vasudhara taal, a large glacial lake located at 4,691 metres above sea level in the Niti Valley, also of Chamoli district. On March 3, the State Disaster Management Authority asked the Wadia Institute of Himalayan Geology to inspect the glacial lake, which has reportedly become larger. According to a local media report, the institute is expected to submit its report in two weeks.
The state government has also decided to geo-map the tonnes of debris deposited on hill slopes, after which it plans to undertake a pilot project for an unspecified river-basin project.
But while studies galore, there has been little action on the ground. Uttarakhand has also conducted a flood zonation exercise, introduced a law to govern the floodplains, put together a ‘Disaster Risk Assessment’, drafted a ‘State Disaster Management Plan’ (vols. I and II); a ‘District Disaster Management Action Plan’ for Chamoli, a ‘Strategic Plan for Risk Reduction’ for Joshimath and Badrinath, and set up an ‘Uttarakhand Risk Database’ of maps and documents to support risk-reduction activities and planning in the state.
(This story was first published by The Science Wire on March 7, 2021 and can be read here.)
