The Central Valley is prone to excessive flooding due to snowmelt from the surrounding Sierra Nevada mountain range in the spring.
A controlled system of dams and canals have been built by state and federal agencies to ensure a steady flow of water into the valley primarily to support agriculture.
Drought years accelerate land subsidence in the Central Valley due to a collective effort of increased groundwater pumping without replenishing underground aquifers.
Land subsides most rapidly during drought years due to the increased pumping and lack of sufficient groundwater recharge.
As the water table falls, competition may occur between farmers to drill deeper underground in order to avoid their well going dry.
During peak demand, the cost of drilling inflates and clients may be put on waiting lists for lengths of time which exceed growing seasons.
The data also revealed that southern El Nido and Corcoran, California were experiencing the most rapid sinking in a bowl shaped manner.
They use InSAR data from NASA's Jet Propulsion Laboratory in conjunction with interferograms to interpret the topographic change captured by satellite imagery.
Continuous Global Positioning Survey station data from UNAVCO, Scripps Orbit and Permanent Array Center, Caltrans, and others are obtained for topography changes over a large region.
Spirit Leveling data from the DWR, Delta-Mendota Water Authority, the Central California Irrigation District, and others are used to measure elevation change in a smaller area.
The USGS uses the data from borehole extensometers provided by the DWR, and also utilizes information from piezometers to track changes in groundwater.
[11] As of 2018, the USGS has been using large hexagonal-shaped sensor rigged to a helicopter to measure groundwater salinity and map underground aquifers in the San Joaquin Valley.
The CVHM considers surface level water supply to estimate groundwater use, as well as monitoring recharge rates.
Infrastructure damage caused by accelerated land subsidence threatens the effectiveness of many dams and canals sourcing surface water to the central valley.
In a 2019 study, researchers found that stretches of the California Aqueduct had sunk in a way that have caused up to 20% loss in carrying capacity of water.