A recent study published in Environmental Research Letters by University of California researchers shows that California’s State Water Resources Control Board has over-allocated to users the amount of surface water available. The board has allowed for withdrawals of 370 million acre-feet, although only 70 million acre-feet are available in the state’s river basins. The researchers analyzed California’s water rights database and compared allocation volumes with modeled predictions of surface water availability. The database includes water rights granted after 1914, which is when the regulatory system currently in use in California began.
The study provides what is described as the first “comprehensive evaluation of appropriative water rights” in California and indicates that approximately five times the state’s mean annual runoff has been allocated to human use. Specifically, the study illustrates that in 16 of California’s 27 major river basins, water allocations are more than 100 percent of natural flows, making it difficult to determine whose supplies to curtail during drought.
The authors state that California’s current framework for managing water rights is likely sufficient to address the need for reform of the system, but any strategy to address these challenges requires an improved ability for the state to account for water availability, movement and use. “To date, the state simply does not have accurate knowledge of how much water is being used by most water rights holders,” the authors state.