The study's lead author, Valerie Trouet, tells Californians to brace for more record dry years and that even the so-called "Godzilla" El Nino — a weather phenomenon expected to bring more rain and snow to the parched West this winter — won't help much.
Ironically, Arizona reservoirs probably will see gains this year because of the El Nino and long-term climate forces that are much different than California's.
Even before the study, snow pack in the Sierra Nevada was known to be exceptionally light. California's in the middle of a severe drought, and data from instrument recordings over the years show the mountains are experiencing an 80-year low in snow.
But the tree-ring findings were surprisingly bad, says Valerie Trouet, an associate professor of dendrochronology at U of A's Laboratory of Tree-Ring Research.
Trouet, Soumaya Belmecheri, and others at the Tucson university authored the report, "Multi-century evaluation of Sierra Nevada snow pack," which is available starting today for a fee at the scientific journal, Nature Climate Change.
California has been under extreme, mandatory drought restrictions since April.
Lack of the stuff isn't the only problem with water in California: It's how water is used there. Only 20 percent of California's treated water, much of it melted snow that came from the Sierra Nevada mountains, is used for urban life. Forty percent of the treated water goes to California agricultural pursuits — which in some cases means growing alfalfa that's shipped to China — while another 40 percent is released back into the state's lakes and streams to help out wildlife.
Trouet's hesitant to declare the Sierra Nevada's ultra-low snowfall in late 2014 and 2015 as definitely because of climate change. However, she's confident that high temperatures had something to do with it. California had its hottest year in 2014, and 2015 could be even hotter.
Because of human-caused global warming, she says, "These type of high temperatures are going to occur more and more frequently," which in turn means bad snow years in the Sierra Nevada could be a lot more common in the future.
To determine snow levels for the past 500 years, Trouet and her colleagues looked at information including previously published tree-ring data from 1405 to 2005, plus recorded measurements since the 1930s, according to the U of A.
So is Arizona up the same dry creek? Not necessarily.
Arizona's water supply is relatively abundant now despite the long-running drought, but it won't be in a few decades after the predicted influx of millions of new and thirsty residents. A naturally occurring drought cycle made worse by climate change has reduced the flow of the Colorado River, which supplies about 40 percent of Metro Phoenix's water but an even higher percentage in drier cities like Tucson.
Yet a tree-ring study conducted by the U of A for the Salt River Project a few years ago showed that a wet year for Arizona has occurred every five years going back 800 years. Trouet says there's no telling whether California's experience this year means Arizona's patterns are due for disruption.
In fact, the likelihood that this year will see a "Godzilla" El Nino effect could help Arizona's drought but leave central and northern California without much relief, she says.
That's because El Nino, the name given to the periodic global weather pattern tied to a rise of temperatures in the Pacific Ocean, usually means more rainfall in Arizona than California, Trouet says.
Experts say this means a good chance of snow pack in the White Mountains, which supply the SRP system and about half the needs of greater Phoenix.
Rainfall is just about average so far this year, says Mark O'Malley, a meteorologist with the National Weather Service in Phoenix. Counting Sunday Night's sprinkling, the Valley's official rainfall total this year is 5.51 inches, a few drops below the average for this time of year of 5.61 inches.
Arizona monsoon storms help make the difference between the droughts in California and Arizona, O'Malley says. While California, which gets almost all of its water from winter storms, has suffered from overly dry weather in the past three years, Arizona "had decent monsoon thunderstorms" during the same period.