California is a semi-arid state in which the availability of water determines land use, and in turn shapes the economy.

That, in a nutshell, explains why Californians have been jousting over water for the state’s entire 174-year history.

The decades of what some have dubbed “water wars” may be approaching a climactic point as climate change, economic evolution, stagnant population growth and environmental consciousness compel decisions on California’s water future.

A new study, conducted by researchers at three University of California campuses, projects that a combination of factors will reduce California’s water supply by up to 9 million acre-feet a year – roughly the equivalent of all non-agricultural human use. They include effects of climate change, new regulations to stem the overdraft of underground water, reducing Colorado River diversions and increasing environmental flows, especially those through the Sacramento-San Joaquin Delta.

In an average year, around 200 million acre-feet of water fall on the state as rain or snow. Evaporation and percolation take most of it, leaving about 80 million acre-feet to be divvied up among three major uses. Agricultural irrigation and environmental flows to the ocean are roughly equal at around 35 million acre-feet while residential, commercial and industrial users take the remainder.

The latter is not only the smallest of the three uses but has been remarkably stable – even declining somewhat, despite decades of high population growth – thanks to intensive conservation programs.

Although water officials constantly beseech Californians to limit their personal consumption of water, the real conflict in recent years, particularly during periods of drought, has pitted agricultural interests against environmentalists over the flows needed to nurture fish and other wildlife.

Environmentalists have pressed state water officials, particularly the Water Resources Control Board, to compel farmers to reduce diversions from rivers to enhance flows. Agriculture is also being squeezed by new restrictions on tapping aquifers via wells. Moreover, California’s largest-in-the-nation agricultural sector has also been shifting from seasonal crops to nuts, grapes and other permanent, high-value products, which need year-round watering.

“Good management and policy for this situation requires organized serious attention and consistent long-term policy, without complacency or panic,” the UC study concludes.

The new study bolsters a 2022 policy paper issued by the Newsom administration calling for 4 million acre-feet of new water storage, another 1.3 million in savings through conservation and reuse of wastewater, and new supplies from desalination and other processes.

The study also arrives as legislation that would set new targets for increased water supply, Senate Bill 366, makes its way through the Capitol with broad support from water interests of all varieties.

It’s one thing to point out that California faces a potential water supply crisis and should be earnestly trying to avoid the effects, but actually doing something confronts two steep hurdles: the glacial pace of water projects of any kind, and unresolved conflict over water rights, some of which date back to the state’s founding in 1850.

The Sites Reservoir exemplifies the former. The western Sacramento Valley project, which would add 1.5 million acre-feet of off-stream storage, has moved closer to reality in recent years after seven decades of sitting on the shelf. Ditto for the long-planned canal or tunnel that would bypass the Sacramento-San Joaquin Delta.

The notion of a comprehensive, long-range program making California’s uncertain water supply more resilient sounds great, and the clock is ticking. However, it assumes that officialdom has the legal authority to make it happen.

Until and unless the issue of water rights is resolved, the much-discussed reallocation of supplies – more for environmental flows and less for agriculture – will remain stalled.

Dan Walters is one of most decorated and widely syndicated columnists in California history, authoring a column four times a week that offers his view and analysis of the state’s political, economic,...