PNAS study: Groundwater over-pumping passes irreversible tipping point in Sacramento Valley

A July 2026 PNAS study identifies a nonlinear threshold where land subsidence from groundwater over-pumping becomes permanent, overturning the assumption that sinking reverses when aquifers recover. Parts of California's Sacramento Valley may have crossed that threshold by 2021, with some areas sinking up to 50 centimeters.