Downscaling GRACE data in the Central Valley aquifer in California

Map showing an example of GRACE TWS.

GRACE TWS example.



Team Location: NASA Ames Research Center, Mountain View, California

Authors: Amber Kuss, University of California, Santa Cruz; Michelle Newcomer, University of California, Berkeley; Wei-Chen Hsu, University of California, Berkeley; Abdelwahab Bourai, Carnegie Mellon University; Abhijit Puranam, St. Francis High School.

Advisors/Mentors: Cindy Schmidt, NASA Ames Research Center, Bay Area Environmental Research Institute; Felix Landerer,, NASA Jet Propulsion Laboratory.

Other Acknowledgements: William Ty Brandt, University of California, Santa Barbara; Joshua Randall, Arizona State University; Bridget Floyd, University of California, Berkeley; Andrew Nguyen, San Jose State University; California Department of Water Resources: Mary Scruggs, Abdul Kahn, Bill Brewster, Charlie Brush; Environmental Protection Agency: Vance Fong.

Abstract: Recent estimates of groundwater (GW) availability in California have indicated declines in GW levels that may pose a threat to the sustainability of this region. The Gravity Recovery and Climate Experiment (GRACE) can be used to estimate variations in total water storage (TWS) and GW storage changes. However, using GRACE data in the Central Valley aquifer (CVA) can be challenging due to the coarse spatial resolution. Climate variability also alters precipitation, GW recharge, and pumping practices. In this study, we used a statistical downscaling approach applied to GRACE data at the sub-region level and then applied the downscaled GRACE estimates to investigate the influence of climate variability, such as from the El Niño Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO). Understanding the effects of climate variability on GW storage changes may improve GRACE-derived estimates of GW availability during periods of increased rain or droughts. Downscaling GRACE-derived GW storage estimates using C2VSim data was successful using linear models at the sub-region level. ENSO and PDO effects on GW elevations and storage in the CVA were assessed using singular spectral analysis (SSA). Results indicated variations in water availability similar to the PDO periodicity. The incorporation of these new methods for estimating variations in GW storage in highly productive aquifers may improve water management techniques in California.

Summer VPS > Water Resources and Oceans