Value of InSAR for Monitoring Land Subsidence to Support Water Management in the San Joaquin Valley, California

Land subsidence because of groundwater extraction in California’s San Joaquin Valley has been occurring for at least nine decades. Historically, in-situ monitoring of subsidence has been limited; the most comprehensive studies and monitoring were associated with construction and operation of large-scale water conveyance infrastructure. Long-term cumulative land subsidence has substantially reduced the conveyance capacity of sections of major canals. The California Department of Water Resources sought NASA’s assistance for remotely sensed satellite- and aircraft-based monitoring of subsidence during the 2012-16 drought. Use of Synthetic Aperture Radar interferometry (InSAR) was highly successful in providing first-ever synoptic measurement of land subsidence over the entire San Joaquin Valley, and in doing so cost-effectively. A key focus of the monitoring was on screening or hotspot detection of impact areas affecting critical water infrastructure. The monitoring revealed that subsidence rates observed during the drought equaled maximum historically observed rates and identified new rapidly emerging hotspots adjacent to critical water infrastructure.