Severe California Drought was the Worst It's Been in Over 1200 Years

It turns out that the drought that has ravaged California is the worst to have occurred in 1,200 years. Now that rain has finally fallen on the dry areas of the state, researchers have shown that the 2012 to 2014 drought was almost unprecedented.

Researchers have watched the severity of the California drought intensify since last autumn. As they did so, they wondered how it would eventually compare to other extreme droughts throughout the state's history. That's why they began to collect new tree-ring samples from blue oak trees in southern and central California.

Blue oak trees are perfect for examining water shortages. They thrive in some of California's driest environments, and are particularly sensitive to moisture changes. More specifically, the tree rings display moisture fluctuations vividly.

Once the NOAA released climate data for the summer of 2014, the researchers used their blue oak data to reconstruct rainfall back to the 13^th century. In addition, they calculated the severity of the drought by combining NOAA's estimates of the Palmer Drought Severity Index (PDSI), an index of soil moisture variability, with the existing North American Drought Atlas, a spatial tree-ring based reconstruction of drought.

"We were genuinely surprised by the result, said Daniel Griffin, one of the researchers, in a news release. "This is California-drought happens. Time and again, the most common result in tree-ring studies is that drought episodes in the past were more extreme than those of more recent eras. This time, however, the result was different."

In particular, researchers found that while there's good evidence of past sustained, multi-decadal droughts, called "megadroughts," these are usually punctuated by occasional wet years. Yet the current short-term drought seems to be worse than any previous span of consecutive drought years without reprieve.

The findings reveal that human-caused climate change could be exacerbating droughts. In addition, the findings may have implications for climate conditions in the future.

"But there is no doubt that we are entering a new era where human-wrought changes to the climate system will become important for determining the severity of droughts and their consequences for coupled human and natural systems," said Kevin Anchukaitis, one of the researchers.

The findings are published in the journal Geophysical Research Letters.