California mega-drought is the worst in 1,200 years

A new study published by the American Geophysical Union concludes that the historic record in tree rings and soil shows that the current drought gripping California is the most severe in 1,200 years — and that 2014 was the worst year of all. Researchers at the University of Minnesota and the Woods Hole Oceanographic Institute say it's the combination of sparse snow and rainfall and higher temperatures that makes this drought worse than others. There have been periods in history with less free water falling out of the sky. And with temperatures rising — well, the droughts in California and the arid West could get measurably worse. This one included.

From a Washington Post Capital Weather Gang story posted this afternoon:

Hidden in this millennium of data they found as many as 66 dry periods of at least three to nine years. In the entire 1,200 year period they studied, there were only three droughts that were similar in nature to the current drought.

Though none have been as severe as what California has seen in the three years since 2012. Not even the historic droughts of the late 1970s, nor the late 1980s. The study also found that 2014 was the worst single drought year in the past 1,200 years, and that approximately 44 percent of California’s 3-year droughts have gone on to last another year, or longer.

The study also found that the current three-year drought, while bad, has not lasted very long historically speaking. In other words, with the Earth's temperature rising, the worst could be yet to come.

A return to normal rainfall levels may partially relieve some of the immediate water resources pressures imposed by the current drought, perhaps through an El Nin ̃o event or a series of landfalling atmospheric rivers. However, the blue oak precipitation reconstruction reveals that the climate system is capable of natural precipitation deficits of even greater duration and severity than has so far been witnessed during the comparatively brief 2012-2014 drought episode….

Future rainfall patterns in California remain unclear, due both to climate model differences and internal climate system variability. However, projections for a continued trend toward higher mean and extreme temperatures are robust and will play an increasingly important role in 21st century hydroclimate, driven by increasing temperatures due to anthropogenic emissions of greenhouse gases and enhanced evaporative demand, are assured and will be a substantial influence on future water resources supply and management in the western United States.