Smaller Colorado River flows predicted – ‘We could be pushing the American Southwest into a permanent state of aridity’

Desdemona Despair

NEW YORK, 24 December 2012 (UPI) – A projected drop in the Colorado River’s flow could disrupt longtime water-sharing agreements between farms and cities in the U.S. Southwest, researchers say.

Climate modelers at Columbia University report a predicted 10 percent drop in the river’s flow in the next few decades may signal water shortages for some 40 million people who depend on the Colorado River Basin for water.

“It may not sound like a phenomenally large amount except the water and the river is already over-allocated,” Richard Seager, a climate scientist at Columbia’s Lamont-Doherty Earth Observatory, said.

The study’s findings suggest the American Southwest is becoming more arid as temperatures rise and rainfall patterns shift from human-caused climate change, and follows a major study of the Colorado River Basin by the U.S. Department of Interior that projected longer and more severe droughts by 2060 and a 9 percent decline in the Colorado’s flows.

“The projections are spot on,” said Bradley Udall, a University of Colorado, Boulder, expert on hydrology and policy of the American West. “Everyone wondered what the next generation of models would say. Now we have a study that suggests we better take seriously the drying projections ahead.” […]

Smaller Colorado River flows predicted

By David Funkhouser
22 November 2012

The American Southwest has seen naturally induced dry spells throughout the past, but now human-induced global warming could push the region into a permanent drought in the coming decades, according to Lamont-Doherty scientist Richard Seager and others who have been studying the area’s climate.

Seager, who focuses on climate variability and climate change, began his work studying droughts by looking into the past using sea surface temperature records gathered by ships plying the oceans in the 19th century. He and colleagues used computer models to recreate a climate history that showed periodic droughts. Focusing on North America, they also used tree rings to look back as far as the Middle Ages, when the Southwest experienced a drought lasting hundreds of years.

“You begin to see that there’s a natural cycle of droughts, large and small,” says Seager, the Palisades Geophysical Institute/Lamont research professor at Lamont-Doherty Earth Observatory. “But when you add in the human effects from rising greenhouse gases, we could be pushing subtropical regions like the American Southwest into a permanent state of aridity. There are signs it’s already underway.”

In a 2007 paper, Seager and colleagues used computer models to show the Southwest is on the verge of a transition to a more arid climate. And in the December 2010 issue of Proceedings of the National Academy of Sciences, Seager and Gabriel Vecchi of NOAA pinned the drying to a drop in winter precipitation and showed how this is caused by changes in atmospheric circulation and water vapor transports induced by warming temperatures.

The warming also shortens the snow season, reduces the snow mass that serves as natural storage for water, and forces an earlier spring melt, disrupting the supply system that waters much of the Southwest—the region from the western Great Plains to the Pacific, and the Oregon border to southern Mexico.

That is ominous news for a region that has seen explosive growth in population, land use, and water demands in recent decades. A reduction in the flow of important water resources such as the Colorado River will have serious consequences.

“I’m curious how the Southwest is going to handle this,” Seager says. […]

Lamont-Doherty Researcher: Southwest Headed for Permanent Drought