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Human-generated climate change has probably made California's historic drought 15 to 20 percent more severe, said scientists from Columbia University's Lamont-Doherty Earth Observatory, NASA's Goddard Institute for Space Studies, and the University of Idaho.
Naturally occurring variations in temperature and rainfall patterns are still the main factors behind the drought, they said. But as climate change pushes temperatures higher, soil, plants, rivers, and lakes require more and more rainfall to compensate for the increased evaporation brought about by the rising mercury.
"A lot of people think that the amount of rain that falls out the sky is the only thing that matters," lead study author Park Williams, a bioclimatologist at Lamont-Doherty said. "But warming changes the baseline amount of water that's available to us, because it sends water back into the sky."
The drought, which according to one study is the worst to hit the region in 1,200 years, is believed to have been caused by a ridge of high-pressure air over the northeast Pacific. The ridge, nicknamed the "Ridiculously Resilient Ridge" by some scientists because of its persistence, is blocking moisture-laden ocean air from making landfall. Scientists remain unsure about the exact cause for the ridge, but a study conducted by Stanford scientists last year found that climate change is likely to make such conditions more frequent.
But even if the ridge is just a whimsy of nature and not a result of climate change, the drought could still be exacerbated by warming global temperatures.
"The timing of wet and dry years is still caused by natural climate variations, but having this underlying trend towards a warmer atmosphere makes the dry years feel worse and the drought effects worse," Williams told VICE News.
The report says that by around the 2060s, more or less permanent drought conditions in California will set in that are likely to be interrupted only by the rainiest years.
The findings, published in the journal Geophysical Research Letters, come at a very crucial time in international climate change discussions. Diplomats will meet in Paris this December to hash out an agreement to curb global greenhouse gas emissions and keep warming to 2 degrees Celsius above pre-industrial levels.
A UC Davis study estimates the drought has brought $1.84 billion of damages to the state's agricultural sector in 2015 and wiped out over 10,000 seasonal jobs. Wildfires have consumed about 144,253 acres of land in California this year, compared to an average of 61,348 acres during the same period over the past five years, according to the California Department of Forestry and Fire Protection.
The states reservoirs are severely depleted and Governor Jerry Brown took the extraordinary step of imposing severe water cuts across the state.
"It's time for Republicans, foot-dragging corporations, and other deniers to wake up and take sensible action before it's too late," Brown said in a statement following the release of the report.
Brown's concerns highlight the plight of California, where some cities rolling out innovative strategies to conserve water. The city of Los Angeles dropped black plastic balls into some of its drinking water reservoirs, the idea being that the floating "shade balls" would shield the water from sunlight, which low evaporation rates.
The study also comes on the heels of NASA report that found continuous pumping of groundwater in response to the drought is making land in California's San Joaquin Valley sink nearly two inches per month in some locations.
Robert Mera, a climate researcher at the Union of Concerned Scientists, told VICE News the situation shows that climate change isn't a far-off threat.
"We are starting to see the impacts," he said.
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