World's largest rivers shrinking

BOULDER, Colorado, April 21, 2009 (ENS) – Many of the greatest rivers in some of the world’s most populous regions are losing water, according to a new study of stream flow in 925 large rivers. Led by scientists at the National Center for Atmospheric Research, the study indicates that the reduced flows are associated with climate change and could threaten future supplies of food and water. Several of the rivers channeling less water serve large populations, such as the Yellow River in northern China, the Ganges in India, the Niger in West Africa, and the Colorado River in the southwestern United States. By contrast, the scientists reported greater stream flow over sparsely populated areas 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 lead author Aiguo Dai a scientist with the National Center for Atmospheric Research in Boulder. “Freshwater being a vital resource, the downward trends are a great concern.” The research team examined stream flow from 1948 to 2004 and found significant changes in about one-third of the world’s largest rivers. Of those, rivers with decreased flow outnumbered those with increased flow by a ratio of about 2.5 to 1. … They found that over the 64 years studied annual freshwater discharge into the Pacific Ocean fell by about six percent, or 526 cubic kilometers – approximately the same volume of water that flows out of the Mississippi River each year. The annual flow into the Indian Ocean dropped by about three percent, or 140 cubic kilometers. But annual river discharge into the Arctic Ocean rose about 10 percent, or 460 cubic kilometers. In the United States, the Columbia River’s flow declined by about 14 percent during the study period, due to reduced precipitation and higher water usage in the West. …

Climate Change Shrinks Some of the World’s Largest Rivers