California is in the third year of one of the state's worst droughts in the past century, one that's led to fierce wildfires, water shortages and restrictions, and potentially staggering agricultural losses.
The dryness in California is only part of a longer-term, 15-year drought across most of the Western USA, one that bioclimatologist Park Williams said is notable because "more area in the West has persistently been in drought during the past 15 years than in any other 15-year period since the 1150s and 1160s" — that's more than 850 years ago.
"When considering the West as a whole,
we are currently in the midst of a historically relevant megadrought," said Williams, a professor at the Lamont-Doherty Earth Observatory of Columbia University in New York.
Megadroughts are what Cornell University scientist Toby Ault calls the "great white sharks of climate: powerful, dangerous and hard to detect before it's too late. They have happened in the past, and they are still out there, lurking in what is possible for the future, even without climate change." Ault goes so far as to call megadroughts "a threat to civilization."
WHAT IS A MEGADROUGHT?
Megadroughts are defined more by their duration than their severity. They are extreme dry spells that can last for a decade or longer, according to research meteorologist Martin Hoerling of the National Oceanic and Atmospheric Administration.
Megadroughts have parched the West, including present-day California, long before Europeans settled the region in the 1800s.
Most of the USA's droughts of the past century, even the infamous 1930s Dust Bowl that forced migrations of Oklahomans and others from the Plains, "were exceeded in severity and duration multiple times by droughts during the preceding 2,000 years," the National Climate Assessment reported this year.
The difference now, of course, is the Western USA is home to more than 70 million people who weren't here for previous megadroughts. The implications are far more daunting.
Overall, "the nature of the beast is that drought is cyclical, and these long periods of drought have been commonplace in the past," according to Mark Svoboda, a climatologist at the National Drought Mitigation Center in Lincoln, Neb. "We are simply much more vulnerable today than at any time in the past. People can't just pick up and leave to the degree they did in the past."
Ault agrees that this long-term Western dry spell could be classified as a megadrought. "But this is not as bad as it could get," he warned.
How do scientists know how wet or dry it was centuries ago? Though no weather records exist before the late 1800s, scientists can examine paleoclimatic "proxy data," such as tree rings and lake sediment, to find out how much — or little — rain fell hundreds or even thousands of years ago.
At the most simplistic level, tree rings are wider during wet years and narrower during dry years.
"Prolonged droughts — some of which lasted more than a century — brought thriving civilizations, such as the ancestral Pueblo (Native Americans) of the Four Corners region, to starvation, migration and finally collapse, " Lynn Ingram, a geologist at the University of California-Berkeley, wrote in her recent book The West Without Water.
Ault says decade-long droughts happen once or twice a century in the Western USA, but much worse droughts, ones that last for multiple decades, occur once or twice per millennium.
Has California reached megadrought status? Not yet: "This one wouldn't stand out as a megadrought," Hoerling said. Even so, "this is the state's worst consecutive three years for precipitation in 119 years of records," he said.
As of Aug. 28, 100% of the state of California was considered to be in a drought, according to the U.S. Drought Monitor. More than 58% is in "exceptional" drought, the worst level. Record warmth has fueled the drought as the state sees its hottest year since records began in 1895, the National Climatic Data Center reports.
Because of the dryness, Calif. Gov. Jerry Brown declared a statewide drought emergency this year. Since then, reservoir storage levels have continued to drop, and as of late August, they were down to about 59% of the historical average.
Regulations restricting outdoor water use were put in place in late July for the entire state. People aren't allowed to hose down driveways and sidewalks, nor are they allowed to water lawns and landscapes (if there is excess runoff). There are reports of wells running dry in central California.
About 1,000 more wildfires than usual have charred the state, including some unusual ones in the spring.
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