A new comprehensive analysis shows that the nearly 3 million rivers that cut the planet are changing faster – and uneven – what scientists expected, with large implications for drinking water supplyecosystems, navigation and risk of floods.
Researchers have used satellite observations combined with computational modeling to reconstruct the daily water flow of each river of the earth in the last 35 years. O.
Almost half (44%) of the largest rivers in downstream regions is carrying less water each year, according to a study published in December 2024 in Science magazine.
Systems that presented significant falls include Congo (the second largest river of Africa), Yangtzé, China, and the River Basin in South America, said Dongmei Feng, the main author of the study and professor of hydrology at the University of Cincinnati.
Small rivers tell another story: in predominantly mountainous regions, 17% showed increased flow.
Although the study has not explored the causes of these changes, the authors claim that the main factors are human activity and the climate crisis driven by fossil fuels, which is altering rain standards and accelerating snow melting.
Previous studies tended to focus only on the largest rivers, producing results limited to specific locations and periods, said Colin Gleason, research co -author and professor of civil and environmental engineering at the University of Massachusetts Amherst.
The methods used in this study allowed “all everywhere at the same time,” he told CNN. Although this does not yet offer the local accuracy of other works, “we believe this is perhaps the most accurate map of the rivers flow ever done,” he said.
Gleason’s conclusion: “My God, the rivers of the world are quite different from what we imagined.” Some are changing 5% or up to 10% per year, the report pointed out. “This is a very, very fast change,” he added.
The rivers are “like Earth’s blood vessels” and changes in their flow have deep effects, said Feng.
downstream mean less water available in the largest extensions of many rivers on the planet, the report points out. This translates into less freshwater for human consumption, crop irrigation and cattle breeding.
Slower flows also reduce rivers’ ability to transport sediments – formed by land and small rocks. This has serious impacts below, as sediments are essential to forming deltas, which offer natural protection against rising sea level.
In smaller rivers, many affected by increasing ice and snow melting with global warming, faster flows can have positive effects, such as providing nutrients for fish and facilitating their migration.
But there are problems. Increased water speed can “launch an unwanted surprise” on hydroelectric plans in regions such as Himalayan, as the more sediment is transported downstream, potentially clogging the infrastructure.
The fastest flow can too. The study identified a 42% increase in large floods in the small mountain rivers over the 35 years analyzed. Gleason quoted Vermont, who has suffered devastating floods in recent summers, the result of factors such as climate change – which are intensifying the strength of the rain – and human interference in the natural flow of rivers.
Hannah Cloke, hydrology professor at the University of Reading, who did not participate in the study, said the comprehensive focus of the research, including even the smallest rivers, is critical.
“Some of the deadliest floods do not necessarily occur in the great rivers you would imagine,” she told CNN. “Instead, they are linked to small rivers or even water courses that are often dry, but suddenly fill and drag people, cars and buildings.”
The next step is to understand exactly why these flows are changing so quickly and how to respond to it.
“There is a direct connection between human activity and changes in our water cycle – essential to life,” said Cloke. Protecting rivers means burning much less fossil fuels, adapting to changes already underway and dealing with the indirect impacts of human actions, such as changing river channels and building in floodplain areas, he added.
“Rivers are dynamic and beautiful creatures,” said Cloke, “and human beings should never underestimate them or waste the resources they provide us with.”
