California’s Central Valley aquifer, the major source of groundwater in the region, suffered permanent loss of capacity during the drought experienced in the area from 2012 to 2015. California has been afflicted by a number of droughts in recent decades, including one between 2007 and 2009, and the millennium drought that plagued the state from 2012 to 2015. Due to lack of water resources, the state drew heavily on its underground aquifer reserves during these periods.