Groundwater provides approximately one third of fresh water used by humans on the planet, but can be vulnerable to depletion during drought-particularly in large, regional aquifers that support irrigated agriculture (Aeschbach-Hertig & Gleeson, 2012;Taylor et al., 2013). Aquifer overdraft occurs where net outflows due to pumping exceed inflows from precipitation, surface-water recharge, and lateral flow, causing declines in groundwater levels and, in some extreme cases, land subsidence (Scanlon et al., 2012;Whittemore et al., 2016). Although physical relationships between pumping and groundwater-level decline have been observed and modeled in a variety of hydrogeologic settings (Butler et al., 2016;Faunt, 2009), effects of aquifer exploitation on water quality are often highly localized, difficult to extrapolate on regional scales, and have only been addressed in a handful of studies (e.g., Blaszyk & Gorski, 1981;Lambrakis & Kallergis, 2001;Nunes et al., 2021). California's Central Valley is a large (51,800 km 2 ), agricultural region that maintains high primary productivity under a semi-arid climate by irrigation from extensive surface-water diversions and groundwater pumpage (Faunt, 2009). Long-term groundwater depletion rates on the order of 2 km 3 yr −1 over the latter part of the 20th century can double during drought as pumpage increases to meet demand shortfalls from diminished surface-water flows (Famiglietti et al., 2011;Faunt et al., 2016). Drought-induced pumpage has precipitated dramatic groundwater-level declines and land subsidence in critically overdrafted groundwater basins within the San Joaquin Valley (SJV) subregion over the past 30 yr (Figure 1a; DWR, 2016DWR, , 2020. Recent work in the Central Valley has focused on vulnerability of shallow, domestic wells to supply failure during drought (Jasechko & Perrone, 2020;Pauloo et al., 2020), but little has been done to connect
