General view of the place where members of NDRF conduct a rescue operation, after a part of a glacier broke away, in Tapovan, Uttarakhand, on Thursday. Reuters

Environmentalists have urged the Indian government to review its policy of building hydropower dams in fast-warming mountain regions, after an apparent glacier collapse this week led to flooding that swept away one dam and left at least 26 people dead.

The Sunday flash flood in India's northern Uttarakhand state, triggered by what scientists said they believed was a large avalanche of glacier ice and rock, left up to 200 people missing in the Himalaya region.

An aerial view of the under-construction Tapovan Vishnugad Hydropower plant project. AP

Rescuers this week were racing to try to free dozens of dam construction workers trapped in a tunnel by debris carried by the wave of floodwater.

Scientists said the disaster was difficult to directly link to climate change in a region where landslides are common — though temperatures are rising faster in the Hindu Kush-Himalaya mountains than in other parts of the region.

But Anil Kulkarni, a glacier expert at the Bengaluru-based Indian Institute of Science, said global warming and "local factors such as deforestation for developmental projects and large-scale construction activities could have contributed to the disaster."

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Continuing construction of hydropower dams in the region needs reconsideration, not just because of warming risks but because of broader environmental impacts, said Sunita Narain, head of the New Delhi-based Centre for Science and Environment.

About 7,000 megawatts worth of hydroelectric projects are already operating or being constructed in the fragile mountains of Uttarakhand, she said.

The projects are going ahead as India tries to move to cleaner renewable energy and provide more power for development, including in more remote regions.

Rescue teams work outside the entrance of Tapovan tunnel. AFP

But such efforts need to be limited by "the carrying capacity of the fragile Himalayan region, which is even more at risk because of climate change", Narain told the Thomson Reuters Foundation.

If dam building continues, more disasters like this week's are likely, she said.

"There is no question that we are going to see more of this, not less, unless we change the way we do business with the environment," Narain said, urging "better-studied decisions on the projects."

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Jigmet Takpa, joint secretary at India’s Ministry of Environment, Forests and Climate Change, said that improving provision of energy in India was crucial for the population's welfare.

Rescue team members work during a relief operation at a destroyed bridge site. Reuters

"Whenever such disasters strike, people start questioning the government. Though it is their right to ask questions, it needs to be understood that natural disasters are beyond the government's control," he told the Thomson Reuters Foundation.

He said India's government and people needed to work together "to develop adaptive strategies to avoid damage", such as ensuring homes are not built near riverbeds.

Reuters