ANTHEM, Arizona, June 7 (Thomson Reuters Foundation) - Carlee Rogers' children run around Anthem Community Park, as she relishes the sunshine. The family moved here from Long Beach eight years ago to escape the rising cost of living, bumper-to-bumper traffic and air pollution in the California port city.
"We wanted a more stable environment for our children to grow up in," said the mother of two.
Twenty years ago, Anthem blossomed from untouched desert land in Maricopa County, 35 miles (56 km) north of downtown Phoenix. Nestled amid clean streets and emerald-green golf courses, rows of sand-colored villas house some 30,000 people.
Anthem follows the model of the low-density, family-friendly suburbs that have sprouted around Phoenix since the 1950s to accommodate the region's surging population.
But further rapid expansion could prove challenging at a time when water supplies are dwindling, as warming temperatures increasingly affect the western United States, scientists warn.
Phoenix is the fifth-largest U.S. city, with nearly 1.63 million people, set to rise to 2.2 million by 2030, according to the U.S. Census Bureau. Residents of the wider metropolitan area are projected to reach 6.3 million by that date, with the highest growth rate in the nation.
To accommodate newcomers, planners and developers are relying on the same method they have used since Phoenix began to grow - targeting large parcels of desert land on its outer ring to build master-plan communities like Anthem.
Belmont, for example, is a development planned for the westernmost fringe of metro Phoenix. Here Cascade Investment LLC, a wealth management firm that counts tech billionaire Bill Gates among its clients, aims to build 80,000 residential units.
And in neighbouring Douglas Ranch, a proposed 34,000-acre (13,759-hectare) community, the master plan allows for 104,000 homes.
Drew Beckwith, water policy manager at Western Resource Advocates, a Boulder-based conservation group, warned such large developments could face problems in the future.
"They may be very risky from a water-supply security perspective," he said.
Located in the western reaches of the scorching Sonoran Desert, Phoenix receives only about 8 inches (20 cm) of rainfall a year.
To supply its citizens, it draws on the Salt and Verde rivers to the east, groundwater aquifers, and the Lake Mead reservoir on the Colorado River.
Last year, scientists at Colorado State University and the University of Arizona said a failure to curb climate change would worsen droughts and bring a very high risk of the Colorado River basin continuing to dry into the future.
Meanwhile, aquifers are being depleted faster than they can replenish naturally, local conservationists have warned, even as some lawmakers push for deregulation of their use.
The Arizona Department of Water Resources requires developers to prove the existence of a 100-year water supply, so that home buyers are assured of adequate water and the new communities do not deplete shared resources.
But finding that evidence is getting tougher.
In Arizona's Pinal County, for instance, at least 15 planned developments hit a roadblock last year after the state cautioned there might not be enough groundwater to support the new housing units, local newspaper The Republic reported.
Jeff Gibbs, a former planning commissioner for the city of Litchfield Park who now writes for The Republic, said state water laws are far-reaching and enforcement is tight.
But the mechanism that compels developers to demonstrate sufficient water supplies will need to be reviewed as the situation evolves, he believes. "Many things impacting water availability can happen in a century," he said by email.
Lake Mead, a mammoth manmade reservoir on the Colorado River that provides about 40 percent of Phoenix's water, is shrinking so fast it is now dangerously close to the level Arizona, California and Nevada - all of which rely on it - consider an official shortage.
In early June, the lake stood at 1,079 feet (329 m) above sea level. By law, mandatory usage cutbacks take effect if it falls below 1,075 feet, which federal forecasters have said could happen as early as 2019.
If the lake's water breaches the alert level, Arizona will be forced to give up 11 percent of its total water allocation, according to the Department of Water Resources.
"The first water users to take a cut... will be from the agricultural community, so the cities will not be affected in the first round of reductions," said Ken Waters, a National Weather Service meteorologist in Phoenix.
Greater Phoenix has yet to declare restrictions on water. Kathryn Sorensen, director of Phoenix Water Services, said the agency was focused on changing behavior in the longer term.
"We encourage customers to embrace a desert lifestyle of wise water use, and give them the information and tools necessary to do so," she explained.
A drought contingency plan is under negotiation between Arizona, California and Nevada, but it is a hard task as everyone affected by its measures must agree, Sorensen said.
"You can imagine it is difficult to convince those that will give up water under the plan to do so for the good of the system," she added.
The city has built up diverse sources of water supplies, which exceed current demand, providing a buffer during dry spells, Sorensen said.
But in the future, severe drought projections and rapid population growth suggest demand will outstrip supply.
Options under consideration include drilling new wells, moving water supplies to where they are needed using transmission mains, and leasing water rights from Native American tribes.
More remote possibilities could be building desalinization plants or piping Great Lakes water west.
Over time, Phoenix has already become more enterprising with its water. "We have been reclaiming and reusing our wastewater for decades," Sorensen said.
And education has pushed residents to embrace a more water-conscious lifestyle.
Water consumption rates have dropped 30 percent in the last 20 years, enabling the city to serve 400,000 more people with the same amount of water, Sorensen said.
"Our advantage in the face of climate change is that (we) understand the value of water in the desert," she said. "Phoenix will stand the test of time."
Reporting by Marcello Rossi; editing by Megan Rowling.
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