Monitoring subsidence with InSAR and inference of groundwater change

Groundwater use is increasing in many parts of the world due to population pressure and reduced availability of surface water and rainfall. California’s Central Valley and southern Arizona in particular have experienced subsidence in many groundwater basins in recent years due to groundwater overdraft. In order to make informed decisions for adaptation, water resource managers need to know the extent of groundwater depletion, both spatially and volumetrically, and to be able to monitor it over long periods. Water wells provide one solution, but owing to remoteness, funding limitations, a lack of wells, and the difficulty of mandating government monitoring of private wells, less direct methods are necessary. Mapping and monitoring subsidence and rebound from orbit with interferometric synthetic aperture radar (InSAR) may provide important indicators of groundwater state and dynamics for water resource managers as well as warnings of potential damage to infrastructure.

We are working with water resource managers at the California Department of Water Resources to produce and update maps of subsidence ‘hot-spots’ where subsidence threatens to cause irreversible aquifer compaction and loss of groundwater storage capacity.

In the future, Germany’s TerraSAR-X, Italy’s Cosmo SkyMed, Japan’s PALSAR-2, Europe’s Sentinels, and NASA’s NISAR offer the promise of extending the time series of observations and expanding this capability to regions of the world with no effective means to monitor the state of their groundwater. This would provide societal benefits to large segments of the global population dependent on groundwater to bridge gaps in surface and rain water supply. As Earth’s climate changes, monitoring of this critical resource will help reduce conflicts over water.

* Work performed under contract to NASA