California is currently experiencing a drought and the state’s water-rights system, which is more than 100 years old, is struggling to cope. Theodore Grantham and Joshua Viers have for the first time identified where, and to what extent, water has been dedicated to human uses relative to natural supplies.

The pair found that some river water basins have been over-allocated by as much as eight times.

“California’s water-rights system has worked in its own dysfunctional way in the past, but it is now struggling to adapt to 21st century realities of increasing water stress, changing climate and societal demands for water-supply security,” Grantham told environmentalresearchweb. “We don’t need major policy reform, we just need to enhance the capacity of California’s State Water Resources Control Board to enforce the laws that already exist.”

California’s water-rights system relies on self-reporting. The amount of water actually used by water-rights holders is poorly tracked and highly uncertain. “You can’t manage what you don’t measure,” said Grantham. “There is an urgent need to increase staffing at the State Water Resources Control Board so that more auditing and enforcement can be carried out.”

Grantham and Viers analysed the state’s water-rights database to estimate the degree of water appropriation in approximately 4000 catchments in California by comparing water-rights allocation volumes with modelled predictions of unimpaired, surface-water availability. They found that water allocated through the state appropriative water-rights system exceeded overall mean water supplies by approximately five times.

The work also highlighted which rivers had the highest levels of over-allocation and found that allocation volumes are greatest for the Sacramento and San Joaquin Rivers and their major tributaries. “This is very worrying because this river helps support a region that grows around 40% of America’s fruit and vegetables,” said Grantham. “The gross over-allocation of water rights, coupled with uncertainty on how water rights are exercised, makes it difficult for water users to know how much water will be available for irrigation, municipal water supply and the environment.”

Water rights are still being issued in many small watersheds, such as the Russian River in northern California, an important region for vineyards and salmon, Grantham says. “But here the Water Board has also recently increased enforcement staff, which we hope will lead to more accurate reporting and improved compliance with water-right terms.”

The researchers were also surprised to find that that the top 1% of water-rights owners account for more than 80% of the total water volume allocated.

“While 78% of water rights are held by private entities, when we looked at the volume of water allocated, we found that 80% was allocated to large public organisations,” said Grantham. “Monitoring these larger organisations should be more straightforward than monitoring many smaller individual water rights holders.”

Grantham and Viers believe their work has highlighted deficiencies in the water-rights system that should be addressed as part of state water-management reforms, and can be used to identify river basins where inaccuracies in water-rights records may impede local efforts to manage water resources efficiently and sustainably.

“With this drought that we are experiencing, it is within everyone’s interest to increase the accuracy of water rights and implement more effective monitoring and reporting systems,” said Grantham.

Grantham and Viers reported their findings in Environmental Research Letters (ERL).

Related links

Related stories