California’s state-run water rights allocation system has given away five times more in volumes than the average annual surface water supplies available through natural runoff, according to California researchers.

In a report published Tuesday in Environmental Research Letters, two researchers with the University of California system said the situation had led to a significant over-allocation of water rights in the state. Recent curtailments of water ordered by the California Water Resources Control Board (WRCB) could have been avoided if the board had an accurate program for allocating surface water supplies, according to authors Theodore Grantham and Joshua Viers. Grantham, now with the U.S. Geological Survey, formerly worked for the Center for Watershed Sciences at the University of California (UC), Davis, and Viers is with the engineering school at UC, Merced.

The “results show that water rights allocations total 400 billion cubic meters, approximately five times the state’s mean annual runoff,” they said in their report, “100 Years of California’s Water Rights System: Patterns, Trends and Uncertainty.”

The authors said the mismatch is not unique to California as recent droughts and “increasing hydroclimatic volatility” throughout the western United States are testing water managers’ ability “to meet diverse and growing demands for supply reliability, improved quality, and healthy ecosystems.” They said the situation has been documented since 1999.

Researchers concluded that all of the emerging water management challenges in semi-arid regions of the world are typified by California, which represents the world’s 10th largest economy with 38 million people. The state has a $40 billion agricultural economy and freshwater ecosystems, according to the WRCB.

In typical non-drought years, California has about 70 million acre-feet of water available in its rivers, reservoirs and other surface resources, the report noted. Water users in the state during those times have the right to withdraw 370 million acre-feet. That’s a 300 million-acre-feet shortfall.

Another anomaly for water managers and industries, such as the oil and natural gas sector, deals with California’s water laws, which are divided into pre- and post-1914 water rights. The WRCB’s unit dealing with water rights said it is “receptive to learning from other parties’ findings regarding allocation of water in post-1914 water rights and ideas on how to improve our processes.” At present, California is not properly enforcing its water rights, the researchers said.

The law also allows for “evolving societal needs and changing environmental conditions,” something that the oil and gas industry may take advantage of over time if unconventional drilling were to increase in the state.

“Improving the scope and implementation of the state’s water rights system is one of many challenges that California must overcome to adapt its water management system to 21st Century conditions,” the report said, drawing on a 2011 study by the Public Policy Institute of California.