Post-drought groundwater storage recovery in California's Central Valley

This paper explores the extent of groundwater depletion in California's Central Valley, which poses a major threat to agricultural and municipal water supply. Recent droughts during 2007–2009 and 2012–2016 exacerbated chronic groundwater depletion. However, it is unclear how much groundwater storage recovered from drought-related overdrafts during post-drought years, and how climatic conditions and water management affected recovery times. This research groundwater storage change in the Central Valley for April 2002 through September 2019 using four methods: GRACE satellite data, a water balance approach, a hydrologic simulation model, and monitoring wells. The research also evaluates the sensitivity of drought recovery to different climate scenarios using water balance method and statistical sampling of historical climate data.

This study finds that estimated Central Valley groundwater loss during the two droughts ranged from 19 km³ (2007–2009) to 28 km³ (2012–2016). Median aquifer storage recovery was 34% and 19% of the overdraft during the 2010–2011 and 2017–2019 post-drought years, respectively. Numerical experiments show that recovery times are sensitive to climate forcing, with longer recovery times for a future climate scenario that replicate historical climatology relative to historical forcing with no droughts. Overdraft recovery times decrease by around two times with implementation of pumping restrictions to constrain groundwater depletion relative to no restrictions with a no-drought future climatology.