In recent years, drought has spread across California like a lengthening shadow, sapping farms and fish, fueling wildfires and forcing towns to scramble for extra water supplies lest taps run dry. It's not the first time, nor will it be the last.

In the coming decades, the situation may become even grimmer. If current models of climate change are borne out, the spring snowpack in the Sierra, a water source for tens of millions of Californians, likely will have dwindled to a shimmering semblance of its former self. Some of the massive aquifers that underlie the bountiful Central Valley croplands may falter from continued overuse. At the same time, California's population, now 38 million, is projected to swell to 46 million by 2035 and then to more than 50 million by 2050.

The Golden State, like much of the parched yet booming West, has reached a crossroads.

"In the past, we have developed a water system that does a great job of meeting our needs—the needs of growing cities, the needs of growing agricultural areas," says Barton "Buzz" Thompson, a Stanford law professor and Perry L. McCarty co-director of the Stanford Woods Institute for the Environment who has become one of the West's foremost authorities on water issues. "But the approaches that we used were not sustainable, and they are at risk of much more extreme drought conditions than we have today."

California has myriad natural advantages, and a few unnatural ones, when it comes to water. The long, high Sierra range serves as a vast reservoir for snow, and beneath much of the state lie rich repositories of groundwater—"drought insurance," as Thompson puts it. And due to sharp historical negotiating, California has first dibs on some of the water from the Colorado River, one of the West's greatest (and most contested) resources.

The state also enjoys the ability to move water around via a comprehensive network of rivers and reservoirs. "The plumbing system of California is incredible," says Terry Anderson, a Hoover Institution senior fellow focused on applying market concepts to environmental issues. "You can almost sit in an office and look at a board with lights flashing or a computer screen and, say, click that valve down three units and that one up three, and move water from Shasta to L.A."

Still, the problems of California and the West have become too pressing to brush aside. Last year was the driest since at least the Gold Rush era, when record keeping began. Even though desperately needed spring rains arrived, they could not make up the deficit. The Sierra snowpack, which comprises a third of the state's water supply, ended the season at just 18 percent of its average level.

More than a dozen small, mostly rural communities nearly ran out of drinking water. In some cases state and local governments had to intervene to help dig new wells or lengthen pipelines. Elsewhere, rivers used by migrating salmon shrank and scientists used boats to ferry struggling young fish to the ocean.

Farmers, who account for about 80 percent of the state's water usage, felt the drought just as acutely. Barred by the state and federal governments from drawing as large a portion of their customary allotment of surface water, many scrambled to salvage long-term investments in valuable crops like almonds and pistachios by pumping water from aquifers. Even so, California's Central Valley, the nation's most prolific producer of fruits, vegetables and nuts, was projected to lose about 6 percent of its irrigated cropland; the financial toll could exceed $1 billion.

Dramatic as this drought has been, with angry Central Valley billboards accusing Congress of creating a new Dust Bowl by favoring endangered species' water needs over farmers', it may merely be a prelude of battles in a future with more people and less water to go around. Across California and the West, "we have very high confidence that continued global warming will increase the likelihood of severely low snow years," says Noah Diffenbaugh, an associate professor in earth sciences and a Woods senior fellow. That is true, he says, even if the world's warming is held to 1 additional degree Celsius, the target agreed to by the United Nations.

Essentially, although precipitation is variable across the Western United States and has actually increased in recent decades in the Southern Sierra, in the coming decades the higher average temperatures predicted by even conservative climate models are likely to turn a larger portion of that snow into rain, as well as hastening melting and evaporation. A smaller snowpack means less of that water will make it into reservoirs and, ultimately, to taps.

The supply situation is worse when aquifers are taken into account. Most years, groundwater accounts for 40 percent of the state's water usage, much of that for agriculture, but in a drought the figure often rises to 60 percent. "We talk about bank accounts for a rainy day; groundwater is our bank account for a dry day," Thompson says. "And we're using up that bank account."

In contrast to most other Western states, groundwater use in California is essentially unregulated at the state level, and local restrictions are a patchwork. Landowners are entitled to draw water that flows beneath their property, but the collective drain can have far-reaching consequences. Overpumping depletes stores faster than they can recharge and can cause the ground to sink. If current practices continue, some experts have warned that California could run out of groundwater in just a few decades. What's more, as the aquifers are depleted, water quality could suffer due to saltwater intrusion.

This is a dreary prognosis, but such outcomes are not inevitable. Thompson, Anderson and other Stanford scholars across a range of disciplines have outlined a series of measures that California can take now to ensure that the water needs of cities, farms and wildlife are met.

The first step toward forestalling future droughts is to gather as much information as possible about water. This may sound obvious, but our knowledge of this invaluable resource has some significant gaps.

Cities are among the fastest-growing users of water, yet some can't accurately measure usage by individual customers. Statewide, some 255,000 homes and businesses in 42 communities lack water meters, according to an investigation of Department of Water Resources records by the San Jose Mercury News. (The newspaper also found that those areas use significantly more water per person than the state average.) In Sacramento, for example, where state lawmakers fret perpetually about water, only about half the homes and businesses have meters. In January, when local officials asked everyone to reduce their water usage by 20 percent, the city couldn't actually tell whether some residents were complying.

Back in 2004, then-Gov. Arnold Schwarzenegger signed a law mandating that all California cities must have meters fully installed by 2025. The intensifying drought has increased the sense of urgency, and some experts have called for accelerating the deadline.

Most farmers in California do not have meters on their groundwater wells, either—a situation mirrored in other large agricultural states like Texas, where meters are seen as not only expensive (costing a few thousand dollars each) but also a slippery slope to regulation. Apart from pumping costs, groundwater is generally free to farms, and lack of data on its use is a serious concern, says Leon Szeptycki, an attorney specializing in water use and management, and executive director of Water in the West, a joint program of the Stanford Woods Institute and the Bill Lane Center for the American West.

Meters could help remedy that. Among other things, they would help with dispute resolution. "If everybody had a meter on their well, and you knew how much everybody was using, and you knew what the aquifer levels are, you could sort of calculate everybody's contribution to aquifer depletion," Szeptycki says. "But if you don't know any of those things, those just become things to fight about."

Farmers counter that they use other means, such as the amount of energy used for pumping, to estimate water use. "Contrary to popular belief, most farms do have some sort of measurement on the water supply," says Mike Wade, executive director of the California Farm Water Coalition. California farms also have been "very proactive in adopting high-efficiency irrigation systems over the last few decades," he adds.

Currently, the state delegates management of groundwater to local authorities, and few of the local bodies have taken aggressive measures to counter aquifers' decline. So despite its reputation as a regulatory minefield, California actually lags behind the rest of the West when it comes to groundwater management. "Most states have taken some action to deal with their most extreme groundwater overdraft," Thompson says. "California is probably the worst. We've probably done the least so far."

That could change, however, as legislation is gathering momentum in Sacramento to increase state oversight of aquifers—a notion that is gaining support even from farmers during this worryingly dry year. Tighter regulations could edge out marginal croplands, Thompson says, but he does not believe it will kill California's farming industry.

Even more basically, California and other states have only limited knowledge about the aquifers themselves. Whereas water in rivers and reservoirs can be measured with reasonable accuracy, we have only a vague idea of how much water lies beneath the Earth's surface, and where it is clean and where it is salty. If this information existed, California could construct a comprehensive map of groundwater resources just as it maps river systems and mountain snowpacks.

The lack of information about the water stored in the state's aquifer system is a problem that Rosemary Knight, PhD '85, a professor of geophysics and Woods senior fellow, by courtesy, has been working on for almost 30 years. Extending Thompson's bank metaphor, she says that our current pump-friendly system "would be like me saying, 'OK, I'm going to retire next week and live off my savings account.' And to see if that's viable, I go to the bank five days in a row and pull out $100—no problem. So I say, 'I'm going to retire and pull out $100 once a week for the rest of my life,' without any knowledge of where the bottom of my savings account is."

Several methods exist for taking the pulse of major aquifers like the Midwest's Ogallala. They range from the low-tech but highly accurate method of sticking a chalked surveyor's tape down a well to aerial surveying of the land's changing mass or physical depression to gauge roughly how much water has been lost in a given region over time. But Knight wants to create an understanding of groundwater system dynamics that is more detailed than the aerial surveys and less labor-intensive and localized than the tape method.

"I often wonder why we all care what the Dow Jones or whatever is doing," she says. "Why don't we talk about what's left in the groundwater aquifers in California?"

To that end, she is working to devise new geophysical methods for probing up to several hundred feet below the surface. Some of the methods involve sending electrical currents or electromagnetic energy into the ground to produce images and get information about porosity, permeability or hydraulic conductivity. The technology Knight is most excited about measures nuclear magnetic resonance—the response of the hydrogen atoms in water molecules to perturbations in the background magnetic field—using equipment laid on the ground or lowered down a well.

In addition to providing vital information about existing groundwater stores, the technology could enable water managers to artificially restock aquifers. The idea, already in limited use nationwide, is to store more rainwater and snowmelt underground, rather than building additional aboveground reservoirs. Conventional reservoirs are difficult to build because they inevitably encounter resistance from landowners who do not want their property flooded. The aboveground lakes are also expensive and lose water to evaporation. Plus, "if you're in earthquake country, there's always the threat of dam failure," Thompson notes.

Underground reservoirs avoid these problems, but they are susceptible to the same common dilemmas that natural aquifers have: There's nothing to keep nearby landowners from simply drilling down and draining water that migrates beneath their property. To prevent this situation, geophysics can help determine where the water in these artificially recharged reservoirs will go, says Knight.

The next inconrovertible step in mitigating the West's water woes is reducing consumption. In practice, though, simply asking people to curtail their water use may not be enough.

"One of the problems right now is water is so cheap throughout the United States that it really doesn't send people the right signals to conserve," says Thompson. The average cost for a gallon of tap water is a fraction of a penny, less than one one-thousandth the cost of the same quantity of milk or gasoline. And the price consumers pay generally reflects the cost of infrastructure—pumping and cleaning the water and maintaining the pipes—rather than the commodity itself.

Yet raising rates raises political hackles, since plenty of Americans take their access to abundant clean water for granted. "The way I like to think about water generally, and droughts particularly," says Anderson of the Hoover Institution, "is that we're not running out of water, we're running out of cheap water."

One remedy, advocated by Thompson, Anderson, Szeptycki and others, is a tiered pricing system in which homes and businesses pay increasing rates the more water they use. The idea is to avoid penalizing modest users, who simply need water for cooking, washing and showering, while discouraging excessive use for luxuries such as lawns, which can easily account for half a household's water consumption.

Such systems are already in place in communities throughout the state and around the country. Thompson points to Irvine Ranch Water District, which serves 340,000 customers over an area of 181 square miles in Southern California, as having an effective tiered pricing system. Since its implementation in 1991, average daily water use by residential customers has decreased by about 50 percent, according to the district.

Anderson and Thompson see universal tiered pricing as part of a broader market-oriented vision that includes buying or trading rights to water. The practice goes back at least to the controversial purchase of water rights in the Owens Valley by the city of Los Angeles in the early 1900s—a transaction that Thompson's grandfather, then a farmer, tried in vain to resist. As yet, trading water rights is not commonplace, but it has been successfully piloted in Oregon and elsewhere.

Anderson believes that it may become an increasingly important tool in the future. It could, for example, allow environmentalists who want to protect salmon runs to pay farmers to leave water in the river. "A market is an institution that links up suppliers with demanders" to help allocate that supply more efficiently, he says. In California, the state can help jump-start markets by making ownership rights to water "clear and more readily transparent and available," and also by smoothing out some of the legal tangles that inhibit water transfers.

In addition to using economic forces to change people's behavior, significantly reducing water consumption in California will require a shift in mind-set, says Szeptycki. He notes that cities in Arizona and New Mexico, having reconciled to surviving in a desert climate, tend to have "much stricter" requirements for making sure that fixtures such as toilets and showers sip water rather than guzzle it. Phoenix also requires developers who want to build new subdivisions to offset the projected water use with a fee to fund new supplies.

"So they're acting appropriately for human beings living in a desert, which in California we're not doing yet."

(This story originally ran in Stanford Magazine.)

The Stanford Woods Institute is finding practical ways to meet growing demand for freshwater, both in developed and developing nations, including the use of recycled water and water resources. Learn more about Woods-sponsored freshwater research.