Imaging the abrupt collapse of the Sacramento Valley 1 aquifer over the 2021-2022 California drought

Ground deformation over aquifer systems reflects changes in water pressure 5 at depth and provides critical insight into groundwater management. Recov6 erable displacement implies sustainable groundwater exploitation, while irre7 versible compaction indicates permanent aquifer damage and compromised 8 long-term groundwater availability. However, the transition between these 9 regimes is not well understood. Here we use space-based and in situ measure10 ments of ground deformation and groundwater levels to capture this critical 11 transition in the Sacramento Valley over the recent California drought. While 12 deformation was primarily poroelastic during the 2016-2020 inter-drought pe13 riod, subsidence accelerated sharply in 2021, indicating significant inelastic 14 compaction and permanent loss of aquifer storage capacity of 0.2 km3/year.