Las Vegas Sun

March 28, 2024

Report: Rivers serving most people, like Colorado, drop as climate changes

Rivers in some of the world's most populated areas, including the Colorado River, are losing water, according to a new study of global stream flows.

Scientists at the National Center for Atmospheric Research (NCAR) examined stream flow from 1948 to 2004 and found significant changes in about one-third of the world's largest rivers.

The study, led by NCAR scientists, suggests that in many cases the reduced flows are associated with climate change, which could potentially threaten future supplies of food and water.

The study says that several of the rivers channeling less water serve large populations, such as the Colorado which flows through seven western states into Mexico and serves 27 million people. Other rivers include the Yellow in northern China, the Ganges in India and the Niger in West Africa.

In contrast, the scientists report greater stream flow in areas with sparse populations near the Arctic Ocean, where snow and ice are rapidly melting.

"Reduced runoff is increasing the pressure on freshwater resources in much of the world, especially with more demand for water as population increases," says NCAR scientist Aiguo Dai, the lead author. "Freshwater being a vital resource, the downward trends are a great concern."

Many factors can affect river discharge, including dams and diverting water for agriculture and industry, Dai says. The study finds, however, that the reduced flows in many cases appear to be related to global climate change, which is altering precipitation patterns and increasing the rate of evaporation. The results are consistent with earlier research done by Dai and others showing widespread drying and increased drought over many land areas.

Dai and his co-authors analyzed the flows of 925 of the planet's largest rivers, combining actual measurements with computer-based stream flow models to fill in data gaps. The rivers in the study drain water from every major land mass except Antarctica and Greenland and account for 73 percent of the world's total stream flows.

Overall, the study found that from 1948 to 2004 freshwater discharge into the Pacific Ocean fell by about 6 percent annually, about the same volume of water that flows out of the Mississippi River each year.

The results will be published May 15 in the American Meteorological Society's Journal of Climate. The research was supported by the National Science Foundation, the National Center for Atmospheric Research's sponsor.

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