This week, southern California received a rare and welcome gift: Rain. An atmospheric phenomenon known colloquially as a “Pineapple Express” channeled Hawaiian precipitation over the continental west coast – by up to ten inches in some places. Yet for all that, the state remains locked in severe drought.

In fact, according to a new study published in the journal Geophysical Research Letters, California’s current drought is the worst it has experienced in the last 1,200 years.

What makes it the worst? Other three-year periods have been drier – similar periods in the late nineteenth and early sixteenth centuries had less rainfall – but the current drought’s combination of dry conditions, low rainfall and high temperatures lend it the “cumulative severity” that makes the 2012-2014 period “stan[d] out in the context of the last millennium.”

The study was co-authored by Daniel Griffin and Kevin J. Anchukaitis, assistant professor in the University of Minnesota’s department of geography and paleoclimatologist at the Woods Hole Oceanographic Institution respectively. The two measured historic precipitation levels by studying the rings of blue oak trees in both central and southern California. These trees’ growth cycles have a particularly strong correlation with rainfall, making them ideal for analyzing past droughts.

By cross-referencing the tree data with soil moisture conditions recorded in the North American Drought Atlas, the scientists arrived at the conclusion that California’s current drought is exceptional in its severity.

“It was a surprise,” Anchukaitis told the Los Angeles Times. “I don’t think we expected to see that at all.”

Given the current temperature trends in California, the finding is perhaps less surprising. Last month, the National Weather Service stated that there is a 99 percent chance that 2014 will be the hottest year in California’s history. Globally, too, all indications point to this year being the hottest since authorities began keeping temperature records.

Unfortunately, one week of rainfall is not enough to change these facts. Jan Null, of Golden Gate Weather Services, recently said that the Pineapple Express precipitation was just “two drops” in the bucket. The past three rainy seasons in San Francisco have been two feet short of the city’s average rainfall.

“The bottom line is we need to make up at least some of the deficit from the past three years,” she told USA Today. “It’s not enough to just pay off this year’s credit card debt, you have to at least pay down some of the previous debt!”

Yet, whenever the current drought finally breaks, Griffin promises it will not be the last.

“One thing is clear,” Griffin told the LA Times. “Drought is going to continue to happen. This is the kind of thing we get to see in the future.”


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