Last spring, an avalanche of ice and rock swept down rivers in northern India and breached two hydropower dams. Over 200 people, mostly dam workers, were killed or went missing.
The incident came eight years after landslides and flash floods topped 10 dams and killed over 6,000 people in the same region.
Scientists are now warning that such disasters could happen more frequently in the high mountain ranges of Asia. Hundreds of new hydropower dams are being built in countries such as China, India and Nepal, near glaciers that are melting due to global warming.
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Authorities should implement better planning, monitoring and early warning systems to prevent catastrophes for the hundreds of millions who could be relying on the dams for power and irrigation, said the scientists in a study published in the Nature Geoscience journal last week.
The paper found that as glaciers melt and retreat to higher altitudes, newly exposed slopes could be unstable and prone to landslides. Data in Asia is incomplete, but the trend has been observed in the European Alps and mountains in New Zealand, the report said.
Flash floods can also occur when melting glaciers break off in large chunks, or when meltwater trapped under thinning ice bursts out. Such incidents could be exacerbated by heavy rainfall – which is already projected to become more frequent in highland Asia due to climate change. The region is warming at a rate double the world average.
Such incidents could cause dam reservoirs to overflow, or the dams themselves to break, wreaking havoc on downstream populations.
The issue is especially prone to happen in the Himalayas, a 2,000-kilometre stretch of mountains that contains some of the world’s highest peaks, according to lead author Dongfeng Li from the National University of Singapore.
“The Himalayas are facing more risks compared to other regions because there are more glaciers there. The glacial retreat in the Himalayas is also faster,” Dr Li said.
It isn’t just more frequent freak events the scientists are worried about. Higher temperatures mean more meltwaters and higher river flows, which bring more sediments into dammed up lakes. The dregs could reduce the storage capacity of dams and wear down turbines for generating electricity.
Sediment load in the Asian highlands will increase by 50 per cent compared to the present levels should global temperatures reach 1.5°C of warming, the paper reported. At 3°C, the load more than doubles.
Better data, planning
There are currently about 100 large hydropower dams in the Asian highlands, spanning the Himalaya, Hindu Kush, Karakoram and Tian Shan mountain ranges. Over 650 new projects are in the planning or building stage, to leverage the huge hydropower potential of the icy mountainous region.
The study said dams designed based on short-term climate records, along with those built close to glaciers, are especially prone to failing.
Professor Lu Xi Xi, a co-author of the study, said existing safety assessments have tended to focus on the dams themselves, but not the entire river basin, where more risks could lie.
Dr Li added that the upcoming changes in sedimentation levels have not been considered in most hydropower plans.
“We need to know whether the designed capacity of current hydropower projects can last long enough for their planned lifespans of roughly five decades,” he said, adding that frequent dredging of sediments could help in maintaining existing dams, along with reforestation of upstream rivers.
Existing dams identified to face flooding risks should also lower their peak summer storage volume to leave more room for contingencies, Prof Lu said, though there will be trade-offs.
“Dam operators may not be willing to do this because that means doing away with income,” he said. Reducing water storage in reservoir dams lowers the electricity generating capacity of the hydropower turbines.
The study said risk maps should be created based on satellite and ground-based research to guide future hydropower development.
“Well-validated, high-resolution, regional-scale maps of mountain permafrost, slope instability, evolving paraglacial landscapes and sediment yields across HMA do not exist, and their absence needs urgent attention,” the report said. HMA refers to High Mountain Asia, the geographical scope of the study.
Early warning systems in high-risk areas could help to save lives, the study added. Such systems have already been successfully implemented in some parts of the region.
The study’s authors say the main issues are not skills and resources of the local communities, but the lack of awareness and funding for scientific research.
Li added that the Asian highlands have high potential for solar power, which could help reduce some of the reliance on hydropower plants. Although hydropower is considered a renewable energy source, huge projects often cause ecosystem damage and uproot local communities.
But giving up on hydropower entirely will not be feasible. Solar panels do not match river dams for stability of power output, Li said.
The dams also help to maintain a constant flow of water in local rivers, which provide communities with farming and drinking water year-round, he added.