Some Droughts Are ‘Perfect.’ Here’s Why
A "perfect drought" happens when major sources of water all experience drought at the same time. It was behind California’s dry spell early last decade, and a new study shows they go back centuries.
Connie Woodhouse and David Meko, professors at the University of Arizona’s Laboratory of Tree Ring Research, found the most recent span of 100 years, when five perfect droughts hit California, was not unusual compared to past centuries.
One perfect drought in the 12th century even lasted nine years, much longer than recent instances.
“These things occurred in the past. There’s no reason that they couldn’t occur in the future, without even talking about climate change,” Woodhouse said in an interview.
The study warns that the potential for longer perfect droughts, coupled with increasing temperatures in the future, could increase the negative effects of a lack of water.
The 2012 to 2015 California drought affected three important water sources for the state: the Colorado River, the Sacramento River and the rainier western portion of Southern California.
Woodhouse said perfect droughts accompany a high pressure air system off the coast of the Pacific Northwest, which keeps storms away from those areas.
The California Department of Water Resources funded the study, as they wanted to know how often perfect droughts happened throughout history.
“They are very interested in understanding the record of the past, to use it as an additional tool in planning for the future,” Woodhouse said.
Water managers in the Colorado River basin have also come to her, wanting to know if a given drought has some echo in the past.
“The question is, ‘oh, is this a climate change drought, or is this the kind of drought that occurred in the past but we just don’t have records long enough to be able to say?’” she said.