NASA Satellites Detect Changes in California’s Central Valley Groundwater

Change in groundwater elevation for the Sacramento hydrological region, in the Central Valley, California. Groundwater elevations were derived from in-situ well-data collected beginning in 2003 by the California Department of Water Resources (DWR). This map displays the changes in groundwater elevation from 2003-2009 derived from the collection of these in-situ measurements. Green areas show groundwater elevation gain and red areas show groundwater elevation loss during this time period.

Change in groundwater elevation for the Sacramento hydrological region, in the Central Valley, California. Groundwater elevations were derived from in-situ well-data collected beginning in 2003 by the California Department of Water Resources (DWR). This map displays the changes in groundwater elevation from 2003-2009 derived from the collection of these in-situ measurements. Green areas show groundwater elevation gain and red areas show groundwater elevation loss during this time period.

Team Location: NASA Ames Research Center

Authors: Amber Kuss, Bridget Floyd, William Brandt, Joshua Randall, Abdelwahab Bourai, Michelle Newcomer

Advisors/Science Mentors: Dr. Jay Skiles, Cyndi Schmidt

Abstract: The Gravity Recovery and Climate Experiment (GRACE) can remotely measure changes in total water storage (TWS) and may minimize the need for well-based data in California’s agriculturally productive Central Valley region. Under California law, land owners are protected from releasing groundwater extraction rates, making monitoring difficult and necessitating the use of other groundwater change detection techniques. From October 2002 to September 2009, GRACE was used to map changes in TWS for the three hydrological regions (the Sacramento River Basin, the San Joaquin River Basin, and the Tulare Basin) encompassing the Central Valley aquifer. Net groundwater changes were calculated from the change in TWS for each hydrological region and by incorporating values for additional components of the hydrological budget including precipitation, evapotranspiration, soil moisture, snow pack, and surface water storage. The calculated change in groundwater storage was then compared to estimates from the Department of Water Resource’s Central Valley Groundwater-Surface Water Simulation Model (C2VISM) and its Water Data Library (WDL) Geographic Information System (GIS) change in storage tool. All three methods produced comparable results. Downscaling GRACE data into the 21 smaller Central Valley groundwater sub-regions, however, produced unreasonable errors for use in decision-making. As a result, the GRACE satellite is a useful tool for characterization of groundwater storage change in large aquifer systems such as the three hydrological regions of the Central Valley aquifer, but not suitable for smaller basins and sub-basins. This work will improve California’s groundwater resource management and use of existing hydrological models for the Central Valley.

Video transcript available here.