Using a combination of computer simulations and statistical techniques, researchers have established a strong link between California’s persistent drought and man-made climate change.
The root of California’s drought is a region of high atmospheric pressure, known as a “blocking ridge,” that has stubbornly lingered over the northeastern Pacific. Stanford University’s Daniel Swain has dubbed this phenomenon the “Ridiculously Resilient Ridge.”
“At its peak in January 2014, the Triple R extended from the subtropical Pacific between California and Hawaii to the coast of the Arctic Ocean north of Alaska,” says Swain.
The ridge diverts high-speed air currents that would normally flow over California, Oregon and Washington up into Alaska and the Arctic circle. The ridge dissipated during the summer of 2013 but returned in the fall, batting away the snow and rain that the west coast would traditionally receive.
As its name suggests, the Triple R is more resilient than meteorologists believe it ought to be. To test this, climate scientist Noah Diffenbaugh of Stanford University organized a team to look at the historical precedent.
Comprehensive atmospheric data is available only from 1948, but no ridges equaled the tenacity of the RRR.
Diffenbaugh’s team then consulted Stanford’s Bala Rajaratnam, who created two climate model simulations – one which utilizes current atmospheric levels of carbon and other greenhouse gases, and one which approximates the atmosphere of a pre-Industrial Earth.
The resulting data shows that the RRR as it appeared at its 2013 height was three times more likely to occur in present atmospheric conditions compared to pre-industrial ones.
According to Diffenbaugh, “Our research finds that extreme atmospheric high pressure in this region – which is strongly linked to unusually low precipitation in California – is much more likely to occur today than prior to the emission of greenhouse gases that began during the Industrial Revolution in the 1800s.”
In August, the U.S. Drought Monitor confirmed that California is officially experiencing its worst drought on record. This has led to mandatory restrictions on home water use and is projected to cost the state’s massive agricultural industry $2.2 billion in direct and indirect losses (plus 17,000 seasonal and part-time jobs).
Nearly half of all U.S.-grown fruits, nuts and vegetables come from California’s central valley, where surface waters have run dry. Farmers are pumping an estimated 62 percent more groundwater to irrigate their crops than in average years, but 410,000 acres have already been lost. The dry conditions have also reduced honey production in the state, leading to a 65 percent increase in retail prices around the country.
Most of the state is suffering what the U.S. Drought Monitor terms “severe” levels of drought, with over 58 percent of the state now in “exceptional” (the highest) drought conditions.
Graphic artist Alvaro Valiño created a gif of the state’s progressive waterlessness for the Los Angeles Times:
California has lost so much water that geologists have actually measured minute changes in the earth’s surface. Without the groundwater that weighed down California’s subsurface rocks, the earth is rising – and putting more pressure on the San Andreas fault.
The Diffenbaugh team’s findings establish a strong correlation between this drought and man-made emissions.
“We’ve demonstrated with high statistical confidence that large-scale atmospheric conditions similar to those of the Triple R are far more likely to occur now than in the climate before we emitted large amounts of greenhouse gases,” says Rajaratnam.
“This isn’t a projection of 100 years in the future,” adds Diffenbaugh. “This is an event that is more extreme than any in the observed record, and our research suggests that global warming is playing a role right now.”
Their research has recently been published in the Bulletin of the American Meteorological Society.