Insights into San Joaquin Valley, California groundwater from GPS-enhanced InSAR surface displacements and in situ data

Abstract:

California’s Central Valley is one of the most productive agricultural regions in the world with an economic output in the tens of billions of dollars (USD). To sustain this level of output, water users rely on an extensive irrigation network consisting of surface water deliveries and groundwater pumping. During anomalously dry periods of time, such as the 2012-2016 drought, surface water availability is reduced which motivates an increased reliance on groundwater resources to meet the water demand. Direct observation of aquifer systems remains challenging due to the sparsity of quality in situ point measurements. However, stress changes in the aquifer related to fluctuations in groundwater levels induce surface displacements that can be observed by remote sensing techniques at much higher spatiotemporal scales.

Here, we investigate land surface displacements over the San Joaquin Valley (SJV; southern two-thirds of the Central Valley) spanning 2015-2019 from Global Positioning System (GPS) stations in the National Science Foundation’s Plate Boundary Observatory network and interferometric synthetic aperture radar (InSAR) from the European Space Agency’s Sentinel-1 missions. We use curve-fitting and multivariate decomposition-based methods to estimate changes in surface displacement patterns on a year-to-year basis. Placing these patterns and the differences in context with general water availability and in situ data where applicable, we draw inferences about groundwater recharge, extraction, and flow across dry and wet time periods. We further explore the efficacy of using surface displacements as an indicator for the timing and location of seasonal groundwater recharge and flow by exploiting periodic observations of groundwater levels from the California Department of Water Resources. We find that deformation in the SJV is complex and can vary on short time scales depending on available surface water supplies. This study provides novel insight into the SJV aquifer system that may contribute to groundwater flow modeling efforts and has relevance to groundwater management.