It’s common practice to use business or banking metaphors when discussing the human use of water; in both cases, the central idea is to exert control, to manage. In its natural state, after all, water tends to be as unpredictable as booms and busts. It arrives as rain or snow, melts, runs into streams or seeps into the ground, floods, evaporates. Through enormous effort and expense, people have been able to corral that irregularity into something that can be relied on, mostly. You assume that your kitchen faucet will run whether or not it has rained recently, just as you expect you can tap into your savings during a recession. Farmers in California’s Imperial Valley, where rainfall averages three inches a year and temperatures routinely exceed 100 degrees, have for a hundred years known that the irrigation water will run so they can plant and harvest the nation’s winter salad crops.
What the managers who operate the water systems are doing is operating accounts. They’re balancing income and expenses, doling out allowances, sometimes running a surplus, sometimes a deficit. And sometimes hiccups occur, just as they do in the financial system. In recent months, some of them have been pretty severe. Just consider a few scenes from the last year in water.
In Southern California, where most of the last 10 years have been drier than usual, water managers last year asked consumers in San Diego to cut back their water usage by 20 gallons a day. Some farmers, meanwhile, faced less-than-voluntary cuts. Due to a previous deal that had provided them with cheap water in exchange for agreeing to be the first to cut back in case of drought, many saw their water supply sliced by 30 percent on Jan. 1. As a result, many have fallowed fields, even cut back avocado trees, to ensure that they can grow some crops with the remaining 70 percent.
These events serve as reminders that, for all the recent hullabaloo about oil — its rising price, its environmental impact, its political volatility — it’s not the only liquid likely to be fought over. Unlike oil, water’s not a cause of recent climate change, and it isn’t in any danger of being used up; indeed, it can be recycled ad infinitum. But there is still grave doubt about whether a warming world will have enough of it.
That can be hard to remember, given that climate change raises sea levels and is suspected of helping spawn monster storms like Hurricane Katrina that dump enormous amounts of rain in a short time. But salt water isn’t potable, and a tropical storm is a blip in the overall cycling of regional climate. What worries hydrologists and climatologists, instead, is the opposite extreme and the ways in which climate change is likely to dry up regions that are already thirsty.
Driven by a newfound sense of urgency, they’re now trying to figure out how people could perhaps adapt to drier conditions with wiser use and a better understanding of how water moves through atmosphere, oceans and air. Though they’re finding that there is a lot of fresh water out there, the most potent lesson they’re learning is this: To stave off water crises in an age of climate change, humans are going to have to manage water, energy and ecosystems together in a system, undeveloped as yet, that takes into account their complex interconnection.
The small town of Orme, Tenn., ran out of water almost entirely last fall, forcing residents to emulate Third World residents in filling up any available containers during the few hours daily when the water was turned on. Low water levels fueled conflict between Georgia and its downstream neighbors, Alabama and Florida, about how much water to release from Lake Lanier, a crucial part of Atlanta’s water supply. Georgia lawmakers have even tried to change the state’s border with Tennessee to take in part of the Tennessee River, which flows tantalizingly just out of reach of the state, apparently as a result of a surveyor’s error made almost two centuries ago.
That’s a comic opera compared to the serious conflicts over water that are taking place on a regular basis in other parts of the world. Control over the vital aquifer that underlies the West Bank has been a consistent source of friction between Israelis and Palestinians. Iraq and Syria have expressed concerns over how much water Turkey extracts from the watersheds of the Tigris and Euphrates rivers, which are vital to their water supply. In 2001, ethnic conflicts and civil unrest shook Pakistan as a result of drought-caused water shortages. Recent food riots in Haiti, Indonesia and other countries have been blamed in part on severe drought that has dramatically curtailed rice production.
Worldwide, one of every five people lacks regular access to safe drinking water, and the United Nations warns that that figure could grow to one in every three by 2025. Against this backdrop, it’s easy to conclude that fights over water supplies may soon eclipse those over other resources, even oil.
“There’s a growing risk of conflict over water, and it’s not just the typical state-versus-state conflict where major rivers cross international borders,” says Peter Gleick, president of Pacific Institute, an Oakland, Calif.-based think tank that has extensively studied water shortages. “It’s going to be farmers versus farmers, farmers versus cities.” He points to Tibet’s ample supplies of fresh water as a factor in China’s interest in the region — a prize, though, whose value may decline as climate change melts its glaciers and dries up the rivers they feed.
All these ups and downs might be explained as the usual give-and-take of weather playing out against a backdrop of increasing human population. In some parts of northern Australia, after all, drought gave way to floods in recent months as heavy rains arrived. Much of the western and northern United States enjoyed ample rain and snow last winter; snowpacks were far above average in Colorado, raising fears of flooding in many towns.
Global warming naysayers are fond of such anecdotes. To climatologists, though, such events are transient blips. Like a good day during a bear market, they have little to do with long-term trends — trends that are, from the perspective of those concerned about water supplies, alarming.
Many scientists have been attempting to refine general models of global climate change — which conclude that the planet is getting warmer as a result of greenhouse-gas emissions — into models that predict what the results of that warming are likely to be in particular regions. In recent years, a consensus has arisen out of this work, and it holds that the Mediterranean, southern Africa and much of the Middle East are among the regions likely to end up holding the short end of the stick when it comes to water supplies.
Another is the American West, especially the Southwest.
“The places that are water-stressed are the places that tend to be pushed into a drier state,” says Chris Milly, a Princeton, N.J.-based research hydrologist with the U.S. Geological Survey. “Global warming is apparently affecting the overall circulation of the atmosphere, including patterns that govern where deserts form.”
That’s generally not because of decreases in rainfall; in fact, a number of regional models project that overall precipitation in the Colorado River basin is likely to remain about the same. Rather, it’s because increased temperatures change the way water moves. More heat means quicker evaporation from rivers, reservoirs and wet soils. In the West, where much high-elevation precipitation has historically fallen as snow, higher temperatures also mean a change in the balance between snow and rain. The former runs off slowly, the latter more quickly. In a warmer world, the same amount of water falling from the sky may result in less water lingering to nourish people, animals or crops.
“With warming temperatures, we’re quite likely in many parts of the West to see a shift from snow to rain,” says Sam Earman, a hydrologist at the Desert Research Institute in Reno, Nev. “That could have a big impact on streams.”
The most dire of recent studies, released in February, suggests that Lake Mead, the giant Colorado River reservoir that nourishes Las Vegas and much of central Arizona, could become unusable by 2021. The study, by Tim Barnett and David Pierce of the Scripps Institution of Oceanography, predicts that even a moderate warming trend could leave the Colorado River basin — which serves as a major water source for seven Southwestern states — much drier than it was during most of the 20th century.
“This water problem is not a scientific abstraction,” Barnett says, “but rather one that will impact each and every one of us who live in the Southwest.”
Though dry locales are likely to bear the heaviest burden, the American Southwest and other arid climes are by no means the only places that will have to contend with uncertain water supplies. In February, Milly and other hydrologists and climatologists published a paper in the journal Science claiming that, as the paper’s title put it, “Stationarity Is Dead.” By stationarity, the authors meant the notion that climate was once broadly reliable. Over the last century, as nations and municipalities intensively developed water supplies, the people charged with water management could readily predict long-term averages for a particular region. Sure, there were dry years and wet, hot spells and cold, but over decades it was possible to chart averages to assess roughly how much water would be available in particular areas. Reservoirs could store the runoff from wet years, making it available during drier periods. That fueled the growth of Phoenix, Las Vegas and the farming mecca of the Imperial Valley, as well as developments in many other regions that face irregular precipitation.
Now, though, the paper’s authors claim, climate change will cause — or has perhaps already caused — significant changes to the water cycle. As a result, predicting what supplies will be available in the future now requires a warning akin to the standard investor’s warning: Past performance is no guarantee of future results. The lack of a track record presents a big challenge to engineers who have to figure out how to get sufficient and consistent water supplies to cities, towns and farms, especially when human populations and water needs keep growing.
“Historically, an engineer has to tell you how big a dam you need, so he looks at the data for the last 50 years and figures out what size dam has a 99 percent probability of being big enough,” Milly says. “He can’t do that anymore because the old record isn’t representative of the future anymore. It’s kind of a daunting task: How do we take the information that we’re beginning to see about climate change and its effects on the water cycle and put it to an engineer working for a given township?
“A lot of people in responding to climate change are kind of going to be flying by the seat of their pants.”
U.S. residents get their drinking water from an aging welter of pipelines, canals and reservoirs, many of them subject to leaks and outright failure because they’re a century or more old. Simply carrying out needed repairs on that network is projected to cost $250 billion over the next couple of decades, according to the American Water Works Association. Worldwide, maintaining and expanding humanity’s freshwater infrastructure is estimated to cost more than $500 billion a year. What happens if a good part of that investment is rendered superfluous by a changing climate — if, say, runoff from the Sierra Nevada or the Tibetan Plateau doesn’t arrive to fill all those expensive reservoirs and canals?
Politicians and water managers have been responding to the double whammy of greater unpredictability and greater need with a number of strategies, not excluding divine intervention; last fall, Georgia Gov. Sonny Perdue convened an hourlong session outside the state capitol to “pray up a storm.” More cold-eyed, there is the old engineer’s strategy: If you’re not sure something is going to work, make it beefier. If runoff is going to become more unpredictable, build higher dams and bigger reservoirs to get you through longer drought periods.
That’s being tried in some places. California officials want to increase the size of a number of dams that store Sierra Nevada runoff. A proposed pipeline in Utah would carry Colorado River water from Lake Powell to fast-growing cities and towns in the southwestern part of the state. Planners in north Georgia are considering converting old reservoirs built to prevent the flooding of agricultural lands into sources of drinking water.
There are a couple of problems associated with these old-school solutions, though, and not just that developing new sources of water these days, when all the best sources have already been taken, lends water agencies the faintly desperate air of a commuter reaching between the cushions, looking for quarters at the tollbooth. One problem is expense. The plan to convert Georgia reservoirs is projected to cost $100 million per lake; the Lake Powell pipeline, more than $800 million. Another is that new or larger dams provoke a lot of resistance from environmentalists and others who don’t want to see such projects built. And a third is that in an era of climate change, there’s simply no guarantee that such projects will have water to fill them.
“If runoff in the Colorado decreases a bit, it doesn’t matter how big your reservoirs are,” Gleick says. “They could be the size of bathtubs or as big as Lake Mead. They eventually run out of water.”
Fine, some engineers say. If all the good freshwater sources are taken, let’s look at some supply of water that hardly anyone thought of using until recently because it’s too salty or too polluted. With modern reverse-osmosis technology, it’s possible to purify just about any water source. That’s how the U.S. military provides fresh water for troops in Iraq.
It’s also what El Paso, Texas, does; last year, the city opened what is believed to be the world’s largest desalination plant that isn’t alongside an ocean. The Kay Bailey Hutchison Desalination Plant has the capacity to produce more than 25 million gallons of drinking water a day from brackish groundwater that was previously considered unusable. A couple of North Carolina counties rich in brackish water have begun constructing similar, though smaller, plants. Water engineers in other arid regions, such as Australia and the Middle East, have also embraced desalination in a big way.
But it’s unlikely to be a panacea. Running a desalination plant produces a lot of extremely salty brine that needs to be discarded somewhere. A plant running on ocean water kills aquatic animals caught in the intake pipes. Perhaps worst of all, desalination takes energy. In an era when the greenhouse-gas emissions fossil fuels produce are getting intense scrutiny, the energy cost of water treatment may outweigh the benefits of using otherwise untapped sources.
Kathy Jacobs directs the Arizona Water Institute, a university consortium that works toward sustainable use of the state’s waters, and she points out that it takes so much energy to deliver and treat water that these two sorts of infrastructure issues can’t be assessed in isolation from one another. “Water and energy are essentially the same thing,” she says. “It requires so much energy to move water, and it requires so much water to create energy, that they are essentially the same resource.”
Another source of low-quality water flows right under your nose any time you drive by a sewage treatment plant. Historically, most observers have placed the emphasis on the first syllable in the word “wastewater,” but that’s changing. The same reverse-osmosis technology that can squeeze salts of out water can squeeze out pathogens and contaminants; in fact, it’s probably the best way to remove the pharmaceuticals and other synthetic contaminants that have been making headlines recently because of their persistence in many water sources.
A number of communities, especially in California, have begun injecting treated wastewater back into aquifers for later withdrawal through wells. Some are even planning to treat wastewater intensively and put it directly into the drinking water supply. But many potential users don’t like the idea of such programs, some of which have been derisively labeled “toilet-to-tap,” even in such water-stressed communities as Tucson, Ariz., and San Diego.
“Technology is a crucial part of future water management,” says Brent Haddad, director of the Center for Integrated Water Research at the University of California, Santa Cruz. “But the trouble is that the technology is way out in front of the social science, policy and regulation. The disgust response isn’t irrational, but it stands in the way of making good decisions about water management.”
That will change, Haddad suggests, as local water crises and costs mount. He says that deliberate reuse of wastewater — as opposed to the sort of inadvertent reuse that takes place when a city dumps its wastewater into a river or lake from which other users take their water — is rising at about 15 percent a year in the U.S.
Conservation, too, is growing, but it remains an elusive goal, in large part because water remains very cheap in most communities in the United States. A Pacific Institute study of Las Vegas’ water use recently concluded that the city could cut its Colorado River withdrawals by 10 percent by implementing simple conservation measures. But the Southern Nevada Water Authority is planning a $2 billion pipeline system to import groundwater from eastern Nevada to the growing city. At a time when Las Vegas has the money and political clout to ship water from elsewhere, there’s simply not that much incentive to conserve.
“The technology exists to do all the things we want with less water,” Gleick says, “but no one is doing it entirely right because the pressure isn’t there.”
Given this uncertainty, it’s no surprise that some managers might be tempted to look down — into the ground, that is, which has been one of the greatest and most reliable sources of water in places where rainfall is irregular.
There’s something like 20 times as much fresh water stored below ground as exists in all the world’s lakes, rivers and streams. A lot of it is hard to get to, but historically that groundwater has made agriculture and development possible in regions where precipitation and rivers can’t be relied on, including the Great Plains, the inland West and northern China. Whether it’s a lonesome ranch windmill filling a single stock tank or a series of giant pumps quenching the thirst of half a million people — as was the case in Tucson until recently — groundwater has often been viewed as the capital that doesn’t diminish, a conservative investment that will pay dividends even in the lean years.
That’s an understandable view. Groundwater doesn’t evaporate, so its behavior isn’t going to change as temperatures increase. And it is buffered from short-term changes in weather patterns; in most places, well levels are roughly the same whether it has rained in the last week or not. As a result, it’s no surprise that some observers think that heavier use of groundwater may help some regions weather climate change. The National Ground Water Association said as much in a position statement issued last year: “Groundwater, the nation’s subsurface reservoir, will be relied on more in the future to help balance the larger swings in precipitation and associated increased demands caused by heat and drought.”
Yet the research the Desert Research Institute’s Earman conducted to earn his Ph.D. at the New Mexico Institute of Mining and Technology makes him doubt how reliable groundwater will be in the face of climate change. He wanted to know how much of the groundwater at four sites in the basin-and-range country of Arizona and New Mexico originated as snow. To do that, he took advantage of an arcane fact: Snow and rain are composed of water with different proportions of hydrogen and oxygen isotopes. He knew that between a quarter and a half of the average annual precipitation fell as snow at his study sites, yet the chemical signatures of the groundwater showed that between 40 and 70 percent of it originated as snow. Snow, it turned out, plays a disproportionately important role in feeding those aquifers.
“The snowpack is like a bank account,” Earman says. “Even though a single snowstorm won’t produce more water than a single rainfall, it adds up in the snowpack into an account that could be made up of snow from 10 to 20 storms. That makes it a much more efficient agent of groundwater recharge than rain.”
As a result, he says, a large-scale shift from snow to rain could cause large decreases in the recharge of aquifers — which would mean that wells have to be drilled deeper and could cause springs and streams to go dry. There are ample examples across the West where excessive groundwater pumping has caused entire rivers to dry up; Earman points to the Republican River in Kansas, where agricultural wells caused a decline of only 3 to 5 percent in groundwater storage — and a 50 percent decline in the river’s flow.
“Western groundwater,” says Mike Dettinger, a hydrologist with the U.S. Geological Survey who collaborated with Earman, “may in fact be very vulnerable to global warming in ways that no one really thought about before.”
Historically, hydrologists have spent a lot more time studying what comes out of the ground than what goes in. They know a lot about how pumping can lower water tables and dry up surface waters and a lot less about how precipitation migrates into the ground. Earman and Dettinger are advocates for a national monitoring network that would meet that need by measuring recharge rates, but it is not in place yet and would not yield any data for quite a while.
A bill that’s been introduced in the Senate, the SECURE Water Act, calls for just such a network. SECURE stands for a mouthful: Science and Engineering to Comprehensively Understand and Responsibly Enhance. But the extent to which comprehensive understanding of groundwater flows would responsibly enhance management strategies is highly uncertain. In most states, streams and groundwater are like a longtime unmarried couple: They’re profoundly linked, yet the legal system doesn’t necessarily recognize a formal connection between them. And the laws governing water use are a confusing amalgam of federal, state, tribal and local regulations and legal rulings. Altering the existing system to reflect new scientific findings, no matter how trenchant, is a daunting task.
“Once you have a huge amount of economic infrastructure based on a particular interpretation, making massive institutional changes becomes very difficult,” says the Arizona Water Institute’s Jacobs. “To the extent that changes in groundwater management would affect existing water rights, there would be legal challenges, and the effort would be unlikely to survive.”
Jacobs worked for the Arizona Department of Water Resources from 1980 through 2000, when the agency implemented a progressive water policy that designates so-called Active Management Areas in the state. In those, municipalities and private developers have to prove that new construction — and the new water uses it brings — will not impinge on the sustainability of groundwater supplies; management debates in one AMA have even explicitly acknowledged links between groundwater and surface water. Jacobs is proud of that accomplishment yet recognizes that if stationarity is dead, even a progressive policy may not suffice.
“In the case of the AMAs, we built into the system a likelihood of failure,” she says, “because we predicted inflows that are higher than what they’re likely to be in the future. We assumed the hydrology is constant. Our water management system can simply no longer be based on assumptions that came out of the past.”
One of the most detailed of recent studies involving a region’s water balance is being carried out along the San Pedro River in southeast Arizona. Using spidery, solar-powered sensors that look like something NASA would send to Mars, researchers from the University of Arizona and other institutions are measuring with great precision how riparian vegetation uses groundwater.
The San Pedro isn’t much to look at as a river, but it supports a stately gallery forest of cottonwood trees that attract birds that, in turn, make this one of the most popular birding destinations in the U.S. It’s also connected to a lot of groundwater in an aquifer that is the sole source of the water used by the fast-growing city of Sierra Vista, Ariz., the Army’s Fort Huachuca and many other human users. As a result, the river is stressed; in 2005, a previously perennial stretch dried up for the first time.
The results of the University of Arizona monitoring project have quantified what scientists had suspected for a long time: namely, that the locally abundant mesquite trees use a lot of water. Mesquites have deep, deep taproots, wells in miniature that can provide them with water even during severe drought, thereby lending them an edge over such competitors as grasses. And they’ve been spreading — because of changes in wildfire regimes, livestock grazing or climate change or because woody plants are generally benefited by higher levels of atmospheric carbon dioxide. No one’s entirely sure why.
Mesquite trees enrich the soil under them, and they furnish good wildlife food and habitat, but in an era of climate change, another service they provide may prove to be more important: They’re long-lived and effective at sequestering carbon. If residents of the arid Southwest decide to get serious about doing what they can to limit concentrations of carbon dioxide in the atmosphere, encouraging the growth of mesquite trees wouldn’t be a bad way to go.
Except for this rub: A mesquite woodland uses a lot of groundwater — more than twice as much as the grasslands that are native to the same terrain.
“We could manage these ecosystems to be very productive, but then they lose a lot of water,” says Travis Huxman, the University of Arizona hydrologist in charge of the project.
At a time when a growing human population is placing more demands on the San Pedro, dedicating more water to plant growth might be a tough sell. What’s going to be more important, regulating the atmosphere or stretching water supplies?
Here’s the final equation to consider, then, in the complex calculations required to manage water supplies: Society’s water balance — and, for that matter, nature’s — can’t be assessed in isolation from its carbon budget. That’s why Huxman, who also directs research at the University of Arizona’s Biosphere 2 facility, has been working with ecologists and hydrologists to design experiments there to better understand plant-groundwater dynamics. And that’s why almost any hydrologist you talk to these days is apt to stress how important it is for water managers to talk to climate scientists, and vice versa. Only through a holistic lens, they say, is there any chance of finding sustainable ways to live with both a changing climate and unpredictable water supplies.
“The problem is that people have been looking at issues sequentially,” Jacobs says. “At least when you start looking at them together you can figure out how to manage both. For example, you can try to optimize both water supply and carbon sequestration. It’s better than trying to manage them as separate problems.”
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