MODELING FUTURE GROUNDWATER DEPLETION TO EVALUATE SUSTAINABILITY GOALS SET BY SGMA IN THE CENTRAL VALLEY, CALIFORNIA, USA (2020-2070)

In 2014, the Sustainable Groundwater Management Act (SGMA) was passed into law with the intention of achieving long-term viability of California’s groundwater resources. Under SGMA, local groundwater sustainability agencies were tasked with creating Groundwater Sustainability Plans (GSPs) that would begin implementation in 2020. These GPSs aim to give transparency into how local groundwater managers propose to achieve long-term sustainability of California’s groundwater basins. To evaluate sustainability goals in these plans, we extracted data from GSPs, focusing on the critically overdrafted basins in California’s Central Valley, to create a database of sustainability indicator wells from these GSPs and their associated groundwater elevation targets for 2040. The resulting database consists of 936 wells from the upper and lower portions of the Central Valley aquifer with groundwater elevation targets ranging from ~60 meters above 2020 water levels to ~80 meters below 2020 water levels. Areas of heterogeneity in elevation targets within and between groundwater subbasins are identified and evaluated in relationship to the GSPs goals against future groundwater depletion scenarios using a regional groundwater model for the Central Valley aquifer system. Simulated scenarios of increased demand result in between 60% and 70% of indicator wells failing to meet groundwater elevation targets by 2040. In simulations with 50% reduction in demand from 2020 demand, close to 40% of wells still fail to meet 2040 elevation goals in the shallow and deep portions of the aquifer. Baseline simulations result in large-scale, transboundary groundwater depletion between groundwater subbasins by 2070 with 70% of wells failing to meet groundwater elevation objectives.