The Central Valley, and particularly the San Joaquin Valley, has a long history of land subsidence caused by groundwater development. The extensive withdrawal of groundwater from the unconsolidated deposits of the San Joaquin Valley lowered groundwater levels and caused widespread land subsidence—reaching 9 meters by 1981. More than half of the thickness of the aquifer system is composed of fine-grained sediments, including clays, silts, and sandy or silty clays that are susceptible to compaction. In an effort to aid water managers in understanding how water moves through the aquifer system, predicting water-supply scenarios, and addressing issues related to water competition, the United States Geological Survey (USGS) developed a new hydrologic modeling tool, the Central Valley Hydrologic Model (CVHM; Faunt and others 2009). For a more detailed description of satellite-based InSAR methods, please see Sneed and others (2013; 2018). For a more detailed description of UAVSAR, please see https://uavsar.jpl.nasa.gov/education/what-is-uavsar.html.
The data presented in this data release was provided by Sneed and others (2013; 2018) and will be used to facilitate updates from CVHM to CVHM2 and represent subsidence observations (measurements) using satellite and airborne Interferometric Synthetic Aperture Radar (InSAR) data during 2003–2016. In the context of this report, subsidence is defined as the lowering of the land-surface elevation as a result of aquifer-system compaction and is calculated by differencing repeated elevation measurements. InSAR methods have been used to monitor land subsidence in the Central Valley and are discussed in more detail in the following sections.