April 21, 2009

Climate Change Reducing Flow Of World’s Rivers

Climate change is resulting in massive drying of some of the world's biggest rivers, according to a report released on Tuesday.

Researchers led by Aiguo Dai of the National Center for Atmospheric Research (NCAR) in Boulder, Colorado found that rivers including the Yellow River in northern China, the Ganges in India, the Niger in West Africa, and the Colorado in the southwestern United States are in danger of losing water due to climate change.

"Reduced runoff is increasing the pressure on freshwater resources in much of the world, especially with more demand for water as population increases," said Dai, whose study appears in the May 15 edition of the American Meteorological Society's Journal of Climate.

"Freshwater being a vital resource, the downward trends are a great concern," Dai added.

Scientists analyzed stream flows in 925 major rivers from 1948 to 2004. They found "significant changes" in about one-third of the largest rivers.

Rivers with a notable decrease in flow outnumbered those with increased flows by about 2.5 to 1, researchers said.

Additionally, they noted increased stream flows in less populated areas near the Arctic Ocean due to snow and ice melting.

Scientists said that including dams and the diversion of water for agriculture and industry are among major factors that influence river stream flow.

From 1948 to 2004, annual freshwater discharge into the Pacific Ocean dropped by about 6 percent, or 526 cubic kilometers, or about the same amount of water that flows out of the Mississippi River each year.

"The annual flow into the Indian Ocean dropped by about 3 percent, or 140 cubic kilometers.  In contrast, annual river discharge into the Arctic Ocean rose about 10 percent, or 460 cubic kilometers," researchers said.

In the US, the Columbia River's flow declined by about 14 percent between 1948-2004. This was linked to the decrease in precipitation and higher water usage in the West.

In contrast, the Mississippi River's flows have increased by about 22 percent during the observation period due to greater precipitation in the Midwest.

"As climate change inevitably continues in coming decades, we are likely to see greater impacts on many rivers and the water resources that society has come to rely on," said NCAR scientist Kevin Trenberth, who co-authored the report.


Image 1: The Colorado River is among rivers worldwide that have been affected by a warming Earth. Credit: Christian Mehlfhrer - Wikipedia

Image 2: River flow trends worldwide between 1948 and 2004 show that many rivers have lower flows. Credit: Courtesy Journal of Climate, UCAR


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