Humans to blame for California drought, say Stanford researchers | Science| In-depth reporting on science and technology | DW | 03.03.2015
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Humans to blame for California drought, say Stanford researchers

California has been suffering an epic water shortage for the past three years. Leading scientists think the worst is yet to come. The culprit: man-made climate change.

For the past three years, California has been weathering the worst drought it has seen in a century. Now scientists at Stanford University in Palo Alto say they have proof that man-made climate change is the cause of the atypical conditions.

Since 2012, traditionally high winter precipitation levels have been down in the Central Valley, the "land of the billion vegetables," where most of California's - and the US's - fruit and vegetables are grown. This will have drastic consequences, the researchers say: Water reservoirs are shrinking at an enormous speed, and the whole valley is literally drying up.

Water conservation signs along Shasta Dam Boulevard in Shasta Lake City, California (Foto: dpa).

Water conservation signs along Shasta Dam Boulevard in Shasta Lake City, California

As a consequence, a quarter of Central Valley fields were crop-free last year, and that cost California's farm industry up to $2 billion (1.8 billion euros). And the dismal news doesn't end there: January 2015 was the driest month on record. Some researchers predict the droughts will continue for the next 200 years, developing into what's known in meteorological parlance as mega droughts.

Noah Diffenbaugh, an associate professor of earth system science at Stanford, has looked at historic climate data and claims that man-made climate change is behind the drought.

"We found that over the course of history low precipitation is important for creating drought, but it's not sufficient," Diffenbaugh said in an interview with DW. "The risk of drought is twice as high when the low precipitations coincide with high temperatures."

Climate change causes the higher temperatures that lead to the drought, the researchers have argued in their study that was published in the US journal Proceedings of the National Academy of Sciences (PNAS). Over the past two decades, there have been more drought years than in the preceding century, they say.

"We know with very high statistical confidence that this warming is very likely due to the human emission of green house gases", Diffenbaugh said.

If the drought continues as Diffenbaugh and his team predict, California will face a summer with severe water shortage that could result in drastic restrictions for its 39 million inhabitants and potentially devastating forest fires.

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