California drought is worst in 500 years – study

© Lucy Nicholson
After four years of drought California is now at its driest for 500 years, scientists have found. The heat has left the Golden State with almost no snowpack in the mountains, which is critical for replenishing the state’s water reservoirs.

An analysis of blue oak tree rings in the state’s Central Valley has led scientists to “astonishing” results

Scientists have compared their measurements of tree-ring data to previous Sierra Nevada snowpack level recordings that have been recorded since the 1930’s and found that oak trees’ growth seem to accurately reflect the lowest snowpack seasons.

“We combined an extensive compilation of blue oak tree-ring series that reflects large-scale California winter precipitation anomalies with a California February-March temperature reconstruction in a reconstruction that explains 63 percent of the Sierra Nevada snow water equivalent variance over the instrumental period,” the scientists wrote.

The answer lies in the rings of Blue oaks that show high winter rain levels with wide bands in the rings, while low levels result in narrow bands.

It became clear after analysis of the new core samples and those taken in previous years that 2015 had the lowest snowpack levels in 500 years.

“The results were astonishing,” Valerie Trouet, an associate professor at the University of Arizona, a senior author for the study, told the Wall Street Journal. “We knew it was an all-time low over a historical period, but to see this as a low for the last 500 years, we didn’t expect that. There’s very little doubt about it.”

READ MORE: ‘This historic drought demands unprecedented action’: California issues 1st mandatory water restrictions

The study was prompted by this April’s measurements of snow in the Sierra Nevada Mountains. State officials announced they had found “no snow whatsoever,” for the first time in 75 years. The snow water equivalent (SWE) stayed “at only five percent of its historical average,” the team of researchers said in a statement.

“In the Mediterranean climate of California, with 80 percent of precipitation occurring during winter months, Sierra Nevada snowpack plays a critical role in the state’s water reservoir and provides 30 percent of its water supplies,” the paper’s introduction reads.

This year’s low snowpack has also coincided with “record-high” January-March temperatures in California. This, scientists warned, can impact “human and natural systems,” including urban and agricultural water supplies and increase risk of wildfires.

California has been cutting water use since April, when the governor Jerry Brown (d) issued the state’s first mandatory water restrictions. Cities and towns were ordered to reduce water usage by 25 percent over nine months hoping to save approximately 1, 5 million acre-feet of water.

This fire season alone, typically from May to January, according to the California Department of Forestry and Fire protections, California has seen about a 1,000 more wildfires compared to last year. The three huge fires currently raging in the northern part of the state have prompted evacuation of thousands of people with a state of emergency declared in the region on Sunday. So far, 400 homes have been destroyed, along with two apartment complexes and 10 businesses.

Director of the governor's Office of Emergency Services Mark Ghilarducci has said this summer's fires are the worst that he has seen in 30 years of emergency response work.

The latest study echoes another piece of research by two climate scientists from the University of Minnesota and Woods Hole Oceanographic Institution, who came to the same conclusion in December 2014. Using the same methodology – analysis of blue oak tree rings – they, however, estimated that the California drought has been the worst in 1,200 years.