The Californian drought is the worst in 1,200 years

According to research carried out by Daniel Griffin from the University of Minnesota and Kevin Anchukaitis from Woods Hole Oceanographic Institution, the current drought in California is the worst in at least 1,200 years.

Here is the latest drought update for California from the US Drought Monitor, which wouldn't include the recent rain. It's for the 2 December - four days ago.

Source: US Drought Monitor

From what I read, it will take quite a bit more than this week's downpours to lift California out of its drought.


In a paper just published in Geophysical Research Letters (GRL), Drs Griffin and Anchukaitis found that this Californian drought was the most severe drought going back at least 1200 years. The abstract:

For the past three years (2012-2014), California has experienced the most severe drought conditions in its last century. But how unusual is this event? Here we use two paleoclimate reconstructions of drought and precipitation for Central and Southern California to place this current event in the context of the last millennium. We demonstrate that while 3-year periods of persistent below-average soil moisture are not uncommon, the current event is the most severe drought in the last 1200 years, with single year (2014) and accumulated moisture deficits worse than any previous continuous span of dry years. Tree-ring chronologies extended through the 2014 growing season reveal that precipitation during the drought has been anomalously low but not outside the range of natural variability. The current California drought is exceptionally severe in the context of at least the last millennium and is driven by reduced though not unprecedented precipitation and record high temperatures.

The press release is at Science Daily. Here are some excerpts:

California finally experiences the arrival of a rain-bearing Pineapple Express this week, two climate scientists from the University of Minnesota and Woods Hole Oceanographic Institution have shown that the drought of 2012-2014 has been the worst in 1,200 years...

...they wondered how it would eventually compare to other extreme droughts throughout the state's history.

To answer those questions, Griffin and Anchukaitis collected new tree-ring samples from blue oak trees in southern and central California. "California's old blue oaks are as close to nature's rain gauges as we get," says Griffin. "They thrive in some of California's driest environments." These trees are particularly sensitive to moisture changes and their tree rings display moisture fluctuations vividly.

As soon as the National Oceanic and Atmospheric Administration (NOAA) released climate data for the summer of 2014, the two scientists sprang into action. Using their blue oak data, they reconstructed rainfall back to the 13th century. They also 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 developed by scientists at Columbia University's Lamont-Doherty Earth Observatory. These resources together provided complementary data on rainfall and soil moisture over the past millennium. Griffin and Anchukaitis found that while the current period of low precipitation is not unusual in California's history, these rainfall deficits combined with sustained record high temperatures created the current multiyear severe water shortages. "While it is precipitation that sets the rhythm of California drought, temperature weighs in on the pitch," says Anchukaitis.

"We were genuinely surprised at the result," says Griffin, a NOAA Climate & Global Change Fellow and former WHOI postdoctoral scholar. "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."

While there is good evidence of past sustained, multi-decadal droughts or so-called "megadroughts"' in California, the authors say those past episodes were probably punctuated by occasional wet years, even if the cumulative effect over decades was one of overall drying. The current short-term drought appears to be worse than any previous span of consecutive years of drought without reprieve.

...So what are the implications? The research indicates that natural climate system variability is compounded by human-caused climate change and that "hot" droughts such as the current one are likely to occur again in the future. California is the world's 8th largest economy and the source of a substantial amount of U.S. produce. Surface water supply shortages there have impacts well beyond the state's borders.

With an exceptionally wet winter, parts of California might emerge from the drought this year. "But there is no doubt," cautions Anchukaitis, "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."

I didn't cut much. You can read the full press release here at ScienceDaily.com.

From the WUWT comments

Despite getting a lot of publicity in the mainstream media, this research hasn't been featured at WUWT so no comments today. It's probably too inconvenient or else Anthony hasn't got around to copying and pasting it under a "claim" headline. Anthony doesn't much like to write about climate change and his home state. However you may recall he has posted a couple of previous articles trying to downplay the severity of this most recent Californian drought, such as here and here.

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Daniel Griffin, Kevin J Anchukaitis. "How unusual is the 2012-2014 California drought?" Geophysical Research Letters, 2014; DOI: 10.1002/2014GL062433