2023 storms refilled LA reservoirs but deep aquifers recovered only a quarter of lost water

Early 2023 brought a series of powerful atmospheric-river storms that dumped unprecedented rain on Southern California, dramatically raising reservoir levels and reviving shallow groundwater near the surface. However, a Science paper reports that deeper groundwater reserves, located more than about 50 metres underground, stayed significantly depleted, recovering merely 25% of the volume lost since 2006. The research team combined conventional groundwater observations with seismic ambient-field interferometry, analyzing decades of seismic recordings to create hydrographs of subsurface water changes.

Their analysis revealed a persistent downward trend in deep aquifer storage despite the wet year, highlighting the slow infiltration process and urban runoff that limit recharge. Lead author Shujuan Mao cautioned that many additional wet years will be required to fully restore these deep reserves. The study warns that surface water recovery can mask ongoing underground deficits, a critical concern for the millions who depend on groundwater in the Los Angeles region.