California’s Central Valley Climate, Groundwater, and Their Interrelated Future – The role of California’s Sustainable Groundwater Management Act (SGMA)

Dr. Claudia Faunt wearing a black shirt smiling

Dr. Claudia Faunt – USGS
Host: Dr. Matthew Weingarten

Wednesday, November 9, 2022
1 pm CLS 422 – or via zoom

Management to ensure the sustainability of California’s water resources is critical. Groundwater is a crucial buffer against land-use change effects, water restrictions, drought, and the impacts of climate change, including the depletion of mountain snowpack that is relied on for part of California’s water supply.  Despite its essential role, the state’s groundwater system is under considerable strain and until recently has been largely unregulated. California’s Sustainable Groundwater Management Act of 2014 (SGMA) provides a framework to comprehensively measure and manage groundwater and empowers local agencies to assess hydrologic issues that may cause “undesirable results.” California’s Central Valley has many basins with “undesirable results,” and most of these are considered “critically overdrafted basins.” The Central Valley covers about 20,000 mi2 and is one of the most productive agricultural regions in the world. Because the valley is semi-arid, surface-water availability varies substantially. Agricultural demand for irrigation is heavily reliant on surface water and groundwater, and in parts of the valley, groundwater pumping has caused severe groundwater-level declines, resulting in land subsidence of up to 30 feet. Starting in the 1950s, state and federal water distribution systems eased reliance on groundwater as dependence shifted to diverted surface water. As a result, groundwater levels recovered, and subsidence virtually ceased for a few decades. In the last 20 years, however, land-use changes and limitations to surface-water availability—including drought and environmental flows—have increased pumping, causing groundwater-level and groundwater-storage declines, renewed subsidence, decreased stream flows, and changes to ecosystems. As these recent trends continue, monitoring and modelling are critical to understanding the dynamics of groundwater use and developing management strategies.  Modeling tools, such as the USGS’s Central Valley Hydrologic Model, enable: (1) Groundwater Sustainability Agencies (GSAs) to have a head start in meeting requirements for key elements of their Groundwater Sustainability Plans, including a hydrogeologic conceptual model, water budgets (past & projected), development of measurable objectives and minimum thresholds, and monitoring network design; and (2) GSAs and state agencies to develop management strategies to mitigate adverse impacts while also optimizing water availability. Such capabilities are critical for successful implementation of SGMA.