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Published: 2019-05-08

Just One-Third of the World’s Longest Rivers Remain Free-Flowing

NEWS The most detailed global assessment ever of the location and extent of the planet’s remaining free-flowing rivers highlights severe degradation. Professor Christer Nilsson at Umeå University and the Swedish University of Agricultural Sciences (SLU) has taken part in the international study, whose remarkable results are now published in the scientific journal Nature.

“Just over one-third (37 percent) of the world’s 246 longest rivers remain free-flowing, according to our study. Dams and reservoirs are drastically reducing the diverse benefits that healthy rivers provide to people and nature across the globe”, says Professor Christer Nilsson of Umeå University and SLU.

A team of 34 international researchers from McGill University, World Wildlife Fund (WWF), and other institutions, among these Umeå University and SLU, assessed the connectivity status of twelve million kilometers of rivers worldwide, providing the first ever global assessment of the location and extent of the planet’s remaining free-flowing rivers.

The researchers determined that only 21 of the world’s 91 rivers longer than 1,000 km that originally flowed to the ocean still retain a direct connection from source to sea. The Earth’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. 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” says lead author Günther Grill of McGill University’s Department of Geography in Canada.

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. That makes it difficult to assess their real impacts across an entire basin or region.

“This first ever map allows us to prioritize and protect the world’s remaining free-flowing rivers, as these are lifelines for wildlife and people across the globe. Rivers provide diverse benefits that are often overlooked and undervalued. Decision makers must consider the full value of rivers when they plan new infrastructure”, says Michele Thieme, lead freshwater scientist at WWF.

Healthy rivers support freshwater fish stocks that improve food security for hundreds of millions of people, deliver sediment that keeps deltas above rising seas, 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 vertebrates globally showed that populations of freshwater species experienced the most pronounced decline over the past half-century, falling on average 83 percent since 1970.

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. Meanwhile, 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 minimize overall environmental and social impact.

“While hydropower inevitably has a role to play in the renewable energy landscape, countries should also consider other renewable options. Well-planned wind and solar energy usually have less detrimental impacts on rivers and the communities, cities, and biodiversity that rely on them,” says Christer Nilsson.

The international community is committed to protect and restore rivers under Agenda 2030 for Sustainable Development, which requires countries to track the extent and condition of water-related ecosystems. This study delivers methods and data necessary for countries to maintain and restore free-flowing rivers around the world.


Original article:

G. Grill et al.: Mapping the world’s free-flowing rivers. Nature. 09 May 2019


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Short facts

· Only 37 percent of the world’s longest rivers remain free-flowing

· Nearly 60,000 large dams exist worldwide, with more than 3,700 currently planned or under construction

· Climate change is a growing threat to river health worldwide, both from direct impacts and as countries increasingly turn to hydropower as a renewable energy option

For more information, please contact:

Christer Nilsson
Professor emeritus