An evaluation of remotely sensed and in-situ data sufficiency for SGMA-scale groundwater studies in the Central Valley, California

California’s Central Valley aquifer represents a critical freshwater resource for the state, providing drinking water to 6.5 million residents and irrigation water for the nation. As a partially non-renewable resource, increasing demands have led to a steady decline of aquifer water levels, leading to irreversible compaction and land subsidence. The Sustainable Groundwater Management Act of California (SGMA), instituted in 2014, requires high-priority regions to establish sustainability plans by 2020-2022 that mitigate groundwater depletion. Here we describe the various in situ and satellite data sets available to support the analysis of SGMA compliance. Many regions within the Central Valley lack groundwater monitoring wells or continuous well data, rendering in-situ monitoring approaches challenging. NASA’s Gravity Recovery and Climate Experiment (GRACE) mission can yield valuable information about groundwater storage changes at sub-basin scale. Interferometric Surface Aperture Radar (InSAR) measurements can map land subsidence, and Global Positioning System (GPS) measurements can describe crustal uplift. Yet, all of these measurements have differences in resolution, coverage, discretization and record length. Here we detail the various datasets useful for Central Valley sub-basins and provide an analysis of gaps and other issues in their sufficiency in the context of SGMA-related analysis. Finally, we offer next steps or recommendations on data treatment and integration.