PNAS study finds groundwater over-pumping crosses irreversible tipping point in Sacramento Valley

A peer-reviewed PNAS study published July 28, 2026 identifies an abrupt, nonlinear tipping point at which land subsidence from groundwater over-pumping becomes permanent — overturning the assumption that subsidence reverses when water levels recover. Parts of California's Sacramento Valley may have crossed that threshold as early as 2021, with some areas sinking up to 50 centimeters.