Two-thirds of world's longest rivers stifled by dams, reservoirs: Study

About two-thirds of the world's longest rivers are no longer free flowing
Two-thirds of world's longest rivers stifled by dams, reservoirs: Study
Two-thirds of world's longest rivers stifled by dams, reservoirs ...

ITDC INDIA EPRESS/ ITDC NEWS Just over one-third of the world's 246 longest rivers remain free-flowing, according to a study which found that dams and reservoirs are drastically reducing the diverse benefits offered by healthy rivers.

A team of international researchers, including those from McGill University in Canada and World Wildlife Fund (WWF), assessed the connectivity status of 12 million kilometers of rivers worldwide.

The study, published in the journal Nature, provides the first-ever global assessment of the location and extent of the planet's remaining free-flowing rivers.

Researchers determined that only 21 of the world's 91 rivers longer than 1,000 kilometres that originally flowed to the ocean still retain a direct connection from source to sea.

The planet's remaining free-flowing rivers are largely restricted to remote regions of the Arctic, the Amazon Basin, and the Congo Basin.

"The world's rivers form an intricate network with vital links to land, groundwater, and the atmosphere," said lead author Gunther Grill of McGill's Department of Geography.

"Free-flowing rivers are important for humans and the environment alike, yet economic development around the world is making them increasingly rare.

"Using satellite imagery and other data, our study examines the extent of these rivers in more detail than ever before," Grill said. Dams and reservoirs are the leading contributors to connectivity loss in global rivers.

The study estimates there are around 60,000 large dams worldwide, and more than 3,700 hydropower dams are currently planned or under construction.

They are often planned and built at the individual project level, making it difficult to assess their real impacts across an entire basin or region.

"Rivers are the lifeblood of our planet," said Michele Thieme, lead freshwater scientist at WWF.

"They provide diverse benefits that are often overlooked and undervalued.

"This first-ever map of the world's remaining free-flowing rivers will help decision makers prioritise and protect the full value rivers give to people and nature," Thieme s

Healthy rivers support freshwater fish stocks that improve food security for hundreds of millions of people, deliver sediment that keeps deltas above rising seas, researchers said.


They also mitigate the impact of extreme floods and droughts, prevent loss of infrastructure and fields to erosion, and support a wealth of biodiversity. Disrupting rivers' connectivity often diminishes or even eliminates these critical ecosystem services.

Protecting remaining free-flowing rivers is also crucial to saving biodiversity in freshwater systems.

Recent analysis of 16,704 populations of wildlife globally showed that populations of freshwater species experienced the most pronounced decline of all vertebrates over the past half-century, falling on average 83 per cent since 1970, researchers said.

The study also notes that climate change will further threaten the health of rivers worldwide.

Rising temperatures are already impacting flow patterns, water quality, and biodiversity.

As countries around the world shift to low-carbon economies, hydropower planning and development is accelerating, adding urgency to the need to develop energy systems that minimise overall environmental and social impact, researchers said.

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