http://mobile.nytimes.com/2015/04/14/science/californias-history-of-drought-repeats.html
The drought,now in its fourth year,is by many measures the worst since the state began keeping records of temperature and precipitation in the 1800s. And with a population now close to 39 million and a thirsty,$50 billion agricultural industry,California has been affected more by this drought than by any previous one.
But scientists say that in the more ancient past,California and the Southwest occasionally had even worse droughts —so-called megadroughts —that lasted decades. At least in parts of California,in two cases in the last 1,200 years,these dry spells lingered for up to two centuries.
The new normal,scientists say,may in fact be an old one.