Climate Change Drying Up Big Rivers, Study Finds
Date: 22-Apr-09
Country: US
Author: Maggie Fox
Climate Change Drying Up Big Rivers, Study Finds Photo: Mario Anzuoni
The Grand Canyon and the Colorado river are seen in Grand
Canyon, Arizona, April 1, 2007.
Photo: Mario Anzuoni
WASHINGTON - Rivers in some of the world's most populated regions are losing
water, many because of climate change, researchers reported on Tuesday.
Affected rivers include the Yellow River in northern China, the Ganges in
India, the Niger in West Africa, and the Colorado in the southwestern United
States.
When added to the effects from damming, irrigation and other water use,
these changes could add up to a threat to future supplies of food and water,
the researchers reported in the American Meteorological Society's Journal of
Climate.
"Reduced runoff is increasing the pressure on freshwater resources in much
of the world, especially with more demand for water as population
increases," Aiguo Dai of the National Center for Atmospheric Research in
Boulder, Colorado, who led the study, said in a statement.
"Freshwater being a vital resource, the downward trends are a great
concern."
Dai's team looked at records of river flow in 925 big rivers from 1948 to
2004, finding significant changes in about a third of the world's largest
rivers.
Rivers with decreased flow outnumbered those with increased flow by 2.5 to
1, they said.
For instance, annual freshwater discharge into the Pacific Ocean fell by
about 6 percent, or 526 cubic kilometers -- about the equivalent volume of
water that flows out of the Mississippi River each year.
Annual river flow into the Indian Ocean dropped by about 3 percent during
the 56-year period, or 140 cubic kilometers.
The Columbia River in the U.S. Northwest lost about 14 percent of its volume
from 1948 to 2004, largely because of reduced precipitation and higher water
usage in the West, Dai's team said.
But the Mississippi River drains 22 percent more water because of increased
precipitation across the U.S. Midwest since 1948, they said.
Annual discharge from melting ice into the Arctic Ocean also rose about 10
percent, or 460 cubic kilometers.
"Also, there is evidence that the rapid warming since the 1970s has caused
an earlier onset of spring that induces earlier snowmelt and associated peak
streamflow in the western United States and New England and earlier breakup
of river-ice in Russian Arctic rivers and many Canadian rivers," the
researchers wrote.
"As climate change inevitably continues in coming decades, we are likely to
see greater impacts on many rivers and water resources that society has come
to rely on," said NCAR scientist Kevin Trenberth, who worked on the study.
(Editing by Vicki Allen)
© Thomson Reuters 2009 All rights reserved
|