California: Indications for continued groundwater depletion after drought and causes of drought variety

Ongoing (2015) severe drought has played a major role in the depletion of groundwater in the state of California. Within California's Central Valley, home to one of the world's most productive agricultural regions, groundwater is being pumped out of aquifers at a rate far greater than the natural rate of replenishment. In general, drought and increased groundwater depletion in the Central Valley occurs almost hand-in-hand but this relationship has changed over the last decade. Data derived from 497 wells and the Gravity Recovery and Climate Experiment (GRACE) have revealed an enhanced depletion of groundwater storage 1-2 years after drought. Possible causes include (a) lengthening of drought associated with amplification in the 4-7-year drought frequency after 2000, and (b) warming trend and increased pumping that enhances depletion. Altogether, the implication is that groundwater resources in the Central Valley will likely continue to diminish even further in 2016, regardless of the drought status.