UC Berkeley

Groundwater management typically relies on water-level data and spatially limited deformation measurements. While interferometric synthetic aperture radar has been used to study hydrological deformation, its limited temporal sampling can lead to biases in rapidly changing systems. Here we use 2011–2017 COSMO-SkyMed data with revisit intervals as short as 1 day to study the response of the Santa Clara Valley (SCV) aquifer in California to the unprecedented 2012–2015 drought. Cross-correlation and independent component analyses of deformation time series enable tracking water through the aquifer system. The aquifer properties are derived prior to and during the drought to assess the success of water-resource management practices. Subsidence due to groundwater withdrawal dominates during 2011–2017, limited to the confined aquifer and west of the Silver Creek Fault, similar to predrought summer periods. Minimum water levels and elevations were reached in mid-2014, but thanks to intensive groundwater management efforts the basin started to rebound in late 2014, during the deepening drought. By 2017, water levels were back to their predrought levels, while elevations had not yet fully rebounded due to the delayed poroelastic response of aquitards and their large elastic compressibility. As water levels did not reach a new lowstand, the drought led to only elastic and recoverable changes in the SCV. The SCV lost 0.09 km3 during the drought while seasonal variations amount to 0.02 km3. Analysis of surface loads due to water mass changes in the aquifer system suggests that groundwater drawdowns could influence the stress on nearby faults.