SOURCE: New Scientist and Nature

DATE: May 8, 2019

SNIP: Nearly two thirds of the world’s longest rivers have had their flow tampered by humans in the form of dams, reservoirs and other forms of water engineering. A boom in hydropower is partly to blame, suggesting we may have been chasing renewable energy at a cost to biodiversity.

The most detailed global assessment yet of long free-flowing rivers finds they have become increasingly rare, confined to remote regions in the Arctic, Amazon and the Congo basin.

An international team spent a decade analysing over 300,000 rivers in global datasets of waterways, including manually checking the location of 25,000 dams against satellite images.

Of the 246 rivers that are 1000 kilometres or longer, just 90 are still free-flowing. Eight of the longest free-flowing rivers are in the Amazon basin.

The big driver has been tapping long rivers for electricity generation, a strategy China and other Asian countries have pursued. Hydropower booms are expected in both the Amazon and Balkans.

“Dam construction is the major reason why river connectivity has been declining worldwide, with often negative consequences on river health,” says Günther Grill of McGill University, who led the work.

Humans have interrupted and diverted the flow of rivers by constructing an estimated 2.8 million dams, as well as building irrigation and water-diversion schemes.

We should care about free-flowing rivers because of the services they provide to humans and wildlife, by allowing the exchange of nutrients, sediment and species, says Grill.