California's 100-year drought: Megadroughts a threat to civilization

California's 100-year drought: Megadroughts a threat to civilization:

 Megadroughts are extreme dry spells that can last for a decade or longer. They have parched the West, including present-day California, long before Europeans settled the region in the 1800s.

http://www.usatoday.com/story/weather/2014/09/02/california-megadrought/14446195/