Western U.S. droughts caused by humans

Water shortages in the western U.S. are not likely to wane any time soon, according to new research that finds human activities are responsible for recent droughts.

Human effects on the climate are causing shrinking snowpack and warmer springs with earlier runoff in the western U.S. River flow CT: “center of timing”, or the day that marks half of the year’s total water flow through the river.

The West has been getting drier for decades. Mountain snowpack is smaller in winter, melts earlier in spring, and leaves rivers running dry in summer. As levels of greenhouse gases increase and warm the climate, these problems will become worse, according to the study, published online January 31 in Science (DOI: 10.1126/science.1152538).

“It’s a train wreck waiting to happen,” says lead author Tim Barnett of Scripps Institution of Oceanography at the University of California San Diego. Changes to water infrastructure in the western U.S. may be “a virtual necessity” to deal with coming shortages in fast-growing dry states, the researchers write.

Barnett and his colleagues examined climate changes in the West during the past 50 years. With computer models that simulate climate for 1600 years, they looked at whether the recent trends could be explained by natural cycles and events alone, such as solar activity and volcanoes. Only by including the human “fingerprint” of rising CO2 levels could the researchers match real-life patterns.

“All of the usual suspects [that can change climate] have been corralled,” Barnett says. “They’ve all been fingerprinted.” The analysis showed that up to 60% of the changes in river flow, snowpack, and winter temperatures from 1950 to 1999 were caused by human activities, such as driving, that produce greenhouse gases.

It’s been clear for many years that the West is getting drier. “But no one had explained why,” Barnett says. If only Mother Nature were to blame, Westerners could wait for the cycle to swing back to a wetter state, he notes. “But it’s us, and it’s going in one direction. And it will only continue to intensify with time.” —ERIKA ENGELHAUPT

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