Domestic well vulnerability to drought duration and unsustainable groundwater management in California's Central Valley

Millions of Californians access drinking water via domestic wells, which are vulnerable to drought and unsustainable groundwater management. Groundwater overdraft and the possibility of longer drought duration under climate change threatens domestic well reliability, yet we lack tools to assess the impact of such events. Here, we leverage 943,469 well completion reports and 20 years of groundwater elevation data to develop a spatially-explicit domestic well failure model covering California's Central Valley. Our model successfully reproduces the spatial distribution of observed domestic well failures during the severe 2012-2016 drought (n = 2,027). Next, the impact of longer drought duration (5 to 8 years) on domestic well failure is evaluated, indicating that if the 2012-2016 drought would have continued into a 6- to 8-year long drought, a total of 4,037 - 5,460 to 6,538- 8,056 wells would fail. The same drought duration scenarios with an intervening wet winter in 2017 lead to an average of 498 and 738 fewer well failures. Additionally, we map vulnerable wells at high failure risk and find that they align with clusters of predicted well failures. Lastly, we evaluate how the timing and implementation of different projected groundwater management regimes impact groundwater levels and thus domestic well failure. When historic overdraft persists until 2040, domestic well failures range from 5,966 - 10,466 (depending on the historic period considered). When sustainability is achieved progressively between 2020 and 2040, well failures range from 3,677 - 6,943, and from 1,516 - 2,513 when groundwater is not allowed to decline after 2020.