The strange discovery about the world's rivers

 

Climate & environment
The shocking discovery about the world's rivers

Wayne Seretis

Published 08.02
 

Quick version

• Scientists have mapped almost three million rivers over 35 years and found that water flow is decreasing in 44 percent of the world's major rivers.
• Decreasing freshwater flows could affect the supply of fresh water and agriculture, while increased flow in smaller rivers could cause more flooding.
• The changes in river flows are believed to be due to human activity and climate change, which affects precipitation and snowmelt.

The Amazon River is included in the mapping that has been going on for 35 years. Photo: Edmar Barros / AP

For 35 years, American scientists have mapped the world's nearly three million rivers.

The result was a shock – water flow is decreasing sharply in almost half of all major rivers.

“Rivers are like the blood vessels of the Earth, and changes in their flow have profound effects,” says Dongmei Feng, a professor at the University of Cincinnati, to CNN.

Scientists already knew that water flow is decreasing in some of our major rivers, such as the world’s largest river, the Amazon.

Now we know that this also applies to 44 percent of the Earth’s several million rivers, a frightening discovery for everyone who depends on freshwater on our planet.

Colin Gleason, a professor of civil and environmental engineering at the University of Massachusetts Amherst, was himself shocked by the discovery.

“Holy cow, the world’s rivers are much more different than we thought,” he tells CNN.

Drought in the Madeira River, a tributary of the Amazon River. Photo: Edmar Barros / AP

Rapid change

The researchers have used satellite images and computer models to map the Earth’s nearly three million rivers over a period of 35 years.

Every single river has been studied daily, and some of the rivers are shrinking by up to 10 percent annually.

“It’s fast, fast change,” says Gleason.

 

          

         Long water flow in the Jialing River in China. Photo: Mark Schiefelbein / AP

 

The trend of decreasing freshwater flows could have serious consequences for our freshwater supply, as well as for agriculture and livestock farming.

“Rivers are like the blood vessels of the Earth, and changes in their flow have profound effects. Rivers like the Congo, the second largest in Africa, the Yangtze, which runs through China, and South America’s Río de la Plata are all showing significant declines,” says Dongmei Feng, a professor of hydrology.

Melting glaciers

At the same time, upstream, near the rivers’ mountain sources, 17 percent of the smaller rivers were seen to have increased flow, likely due to melting glaciers.

The study did not delve into the causes of the decline, but the authors say that the clear causes are human activity and the fossil-fueled climate crisis, which is changing rainfall patterns and accelerating snowmelt.

In addition to reduced access to drinking water, irrigation and drinking water for livestock, reduced flows mean that rivers are carrying less sediment, which is the building block of river deltas that, among other things, provide natural protection against rising sea levels.

A river in India that has overflowed its banks. Photo: Prakash Adhikari / AP

Deadly floods

The greatly increased flows in smaller rivers are also suspected of being behind many floods. The researchers saw a 42 percent increase in major floods that came from smaller source flows.

– Some of the deadliest floods do not necessarily come from the big rivers as you would expect. Instead, they are linked to small and even normally dry rivers that suddenly fill with water and sweep away people, cars and houses, says Hannah Cloke, a professor of hydrology who commented on the report for CNN.

“Rivers are dynamic and beautiful beasts, and humans should never take them for granted or neglect the resources they provide us,” she says.