Groundwater is a precious and limited resource that is used in meeting the needs of California’s large and small urban areas, rural groundwater users, irrigated agriculture, and the environment. Since the last California’s Groundwater (CalGW) Update in 2003, there has been significant changes to land use, water use, water application practices, and water allocations. In addition, the effects of climate change have affected California’s reliance on groundwater. It is expected that there will be additional changes in land use, water use, adjustments in water allocations, and that climate change will continue to affect the environment, thus elevating the importance of the reporting in CalGW Updates.
According to the last comprehensive report, California’s Groundwater Update 2003 (CalGW Update 2003), California’s reliance on groundwater was approximately 30 percent during a wet-to-average precipitation water year and approximately 40 percent during dry periods. Since then, the percentage of groundwater reliance has increased to between 30 and 40 percent during above normal to-wet years and to as much as 58 percent during dry periods (California Department of Water Resources 2018).