Water securityDroughts caused permanent loss to major California groundwater source

Published 20 March 2019

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’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.

According to new research, the San Joaquin Valley aquifer in the Central Valley shrank permanently by up to 3 percent due to excess pumping during the sustained dry spell. Combined with the loss from the 2007 to 2009 drought, the aquifer may have lost up to 5 percent of its storage capacity during the first two decades of the 21st Century, according to Manoochehr Shirzaei, an assistant professor of earth sciences at Arizona State University in Tempe and one of the co-authors of a new study published in AGU’s Journal of Geophysical Research: Solid Earth.

AGU notes that groundwater exists in the pore spaces between grains of soil and rocks. When fluids are extracted from aquifers, the pore spaces close. There is a range for which these spaces can shrink and expand elastically. But if the pore spaces close too much, they start to collapse, causing the land to shrink irreversibly.

Figuring out how much the aquifer shrank permanently could help water managers prepare for future droughts, according to the study’s authors. The San Joaquin Valley aquifer supplies freshwater to the Central Valley – a major hub that produces more than 250 different crops valued at $17 billion per year, according to the U.S. Geological Survey.

“If we have even one drought per decade, our aquifers could shrink a bit more each time and permanently lose more than a quarter of their storage capacity this century,” said Susanna Werth, a research assistant professor of earth sciences at Arizona State University, and a co-author of the new study.