Subsidence – the gradual caving in or sinking of land – is significantly limiting California’s water delivery capabilities. A recent technical report confirms that this land collapse, primarily driven by groundwater over-pumping impacts, already affects deliveries and could drastically reduce them without immediate, substantial action.
This subsidence occurs when excessive groundwater is withdrawn from aquifers, causing the overlying land to compact. While a known issue, the report quantifies its accelerating effect on the State Water Project (SWP). The SWP is California’s critical water network, serving millions of residents and vast agricultural areas.
Current data indicate subsidence has already reduced the SWP’s annual water delivery capacity by 3%. Projections for 2043 are stark: without intervention, continued subsidence combined with climate change could diminish SWP deliveries by an unprecedented 87%. This presents a fundamental challenge to California’s long-term water reliability.
The 2024 Delivery Capability Report (DCR) had previously noted that climate change could reduce SWP reliability by 23% in 20 years. This new addendum specifically details how subsidence damages major SWP canals. Groundwater over-pumping creates depressions or “bowls” along these canals, impeding water flow and restricting volume. SWP operators have adapted for years, but operational limits have been reached; water now runs dangerously close to canal liner tops in affected areas.
The long-term outlook for the future of the State Water Project is critical. Under moderate to extreme conditions, annual deliveries could fall by 400,000 to 1.5 million acre-feet. These figures indicate that unaddressed subsidence will hinder the state’s ability to store water during wet periods and diminish supplies for drought resilience, impacting overall water infrastructure resilience.
The report underscores the critical role of the Sustainable Groundwater Management Act (SGMA) and the urgent need for basins to achieve sustainable management.
The Department of Water Resources (DWR) is actively implementing solutions. These include projects to restore SWP capacity, collaboration with Groundwater Sustainability Agencies (GSAs) to halt subsidence through effective management, and efforts to secure vital funding for these initiatives. These strategies are essential for strengthening water infrastructure resilience and safeguarding California’s water future.
