Many rivers around the world are losing water due to global climate change, according to a new study from the American Meteorological Society’s Journal of Climate. Large populations depend on some of the rivers for everything from agriculture to clean drinking resources, including the Yellow River, the Ganges, the Niger, and the Colorado, which have all shown significant declines.
“The distribution of the world’s fresh water, already an important topic will occupy front and center stage for years to come in developing adaptation strategies to a changing climate,” says Cliff Jacobs of National Science Foundation, which funded the research.
Scientists from the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, examined stream flows from 925 of the world’s largest rivers for over fifty years, 1948 to 2004. Using measurements from the field supplemented by computer models, the scientists found that one third of the rivers showed large changes in stream flows with these, either gaining water or losing it. A decrease in water flow was more common, outnumbering an increase by a ratio of 2.5 to 1. In addition, rivers that were experiencing larger stream flows were usually in little-populated areas, such as the Arctic where melting ice is inundating river systems.
The Colorado River as seen from the inside of the Grand Canyon. The river has dropped 14 percent in less than sixty years. Photo by: Rhett A. Butler.
The researchers found that freshwater making its way into the Pacific Ocean has fallen by 6 percent, about the same volume as the annual freshwater discharge from the Mississippi every year.
“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 of the journal paper. “Freshwater being a vital resource, the downward trends are a great concern.”
The researchers have linked these changes in water flow to climate change. While, other factors are involved including dams and irrigation, the researchers found that largest changes to be linked to shifting climate patterns, including altered precipitation and increasing evaporation due to warmer temperatures.
While the change in river levels will have immediate impacts on food and water security for nations across the world, scientists are also concerned about how less freshwater may affect the oceans. Many of these rivers’ freshwater discharges bring nutrients and minerals to the oceans, important for many marine species. As well the freshwater from river systems affects oceanic circulation, which could exacerbate climate change. The scientists say that possible shifts in the ocean must be closely monitored in the future.
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