Groundwater & Land Subsidence — Antelope Valley
Lancaster · the basin that pioneered InSAR subsidence measurementAs groundwater is pumped faster than it recharges, the water table falls and the fine-grained clays compact — sinking the land surface. When heads drop below their historical low, that compaction is permanent. Below: groundwater elevation (blue, left axis) against land subsidence measured by satellite radar (orange, right axis).
Reading the chart
- Groundwater has fallen for decades — the historical well (dashed) dropped ~150 ft from the 1940s, and the current well shows the decline continuing through today.
- The land is now measurably sinking — Sentinel-1 InSAR records steady subsidence since 2015 (a few inches), each interferogram the phase difference between two radar passes, GPS-referenced by DWR.
- Subsidence is only partly recoverable. The seasonal elastic "breathing" rebounds when water levels recover; the inelastic compaction — once heads pass their historical low — is permanent, and so is the lost storage capacity.
The Antelope Valley is where this was first proven: Galloway et al. (1998) used ERS radar interferometry here, validated against a borehole extensometer and well levels — the founding study for satellite groundwater-subsidence monitoring. GRACE gravity satellites are too coarse to resolve this basin; InSAR + wells are the right tools.
- Subsidence — CA DWR / TRE Altamira, Sentinel-1 InSAR (2015–present)
- Groundwater — CA DWR periodic groundwater-level measurements
Provisional data subject to revision. Public agency observations only — no causal or policy interpretation.