Depth-dependent seismic sensing of groundwater recovery from the atmospheric-river storms of 2023.

In early 2023, a series of intense atmospheric-river storms eased California's historic drought, yet the spatiotemporal extent of groundwater recovery remains poorly understood. We tracked two-decadal changes in groundwater in Greater Los Angeles using seismic ambient-field interferometry. The derived seismic hydrographs reveal distinct expressions of groundwater and surficial water droughts: Whereas surface and near-surface water storage nearly fully recovered in the epic wet season of 2023, only about 25% of the groundwater lost since 2006 was restored. On a decadal scale, we find substantial depletion in aquifers below 50-meter depth, with only limited storm-related recovery. Our analysis underscores the need to monitor deep aquifers for a more complete assessment of total water deficits, using high-resolution tools such as seismic sensing.