More than half of the world's rivers run dry each year

More than half of the world’s rivers run dry each year In a new study led by McGill University, researchers have determined that more than half of the world’s rivers and streams stop flowing for at least one day per year. The experts found that between 51 and 60 percent of the 64 million kilometers of Earth’s rushing waters run dry periodically.

The research highlights the need to change the general assumption that water flows in rivers and streams year-round. The study has also produced a map of non-perennial rivers that provides crucial baseline information for the assessment of future changes in river flow intermittence. North America is a continent entirely within the Northern Hemisphere and almost all within the Western Hemisphere. It can also be described as the northern subcontinent of the Americas. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Caribbean Sea, and to the west and south by the Pacific Ocean. Because it is on the North American Tectonic Plate, Greenland is included as part of North America geographically. North America covers an area of about 24,709,000 square kilometers (9,540,000 square miles), about 16.5% of the Earth’s land area and about 4.8% of its total surface. North America is the third-largest continent by area, following Asia and Africa,

“Non-perennial rivers and streams are very valuable ecosystems as they are home to many distinct species that are adapted to cycles of water presence and absence,” said study first author Mathis Messager.

“These rivers can provide critical water and food sources for people and they play an important role in controlling water quality. But more often than not they are mismanaged or altogether excluded from management actions and conservation laws as they are simply overlooked.”

Study co-senior author Professor Bernhard Lehner noted that given continued global climate and land use change, an increasingly large proportion of the global river network is expected to cease to flow seasonally over the coming decades.

“In fact, many formerly perennial rivers and streams, including sections of iconic rivers such as the Nile, the Indus and the Colorado River have become intermittent in the past 50 years due to climate change, land use transitions, or the temporary or permanent withdrawal of water for human use and agriculture.”

The researchers analyzed long-term records of water flow in 5,615 locations around the world. The data included information on the hydrology, climate, and surrounding land cover at these locations. 

The experts determined that non-perennial rivers are most common in places where there is much more evaporation than rainfall. They also found that smaller streams have more variable flow, which makes them more likely to dry up periodically. 

Surprisingly, the study showed that non-perennial rivers occur in tropical climates – and even in the Arctic – where rivers freeze up for parts of the year.

The researchers estimate that more than half of the world’s population lives in locations where the closest river or stream around them is non-perennial. 

“By mapping non-perennial rivers and streams, our study pushes for a recognition of their prevalence and ecological significance by the scientific community,” said co-senior author Thibault Datry. 

“We hope that our study will trigger efforts to adequately manage these river ecosystems and halt attempts to exclude them from protective legislation.”

The study is published in the journal Nature.

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By Chrissy Sexton, Earth.com Staff Writer