When the conditions are just right – winds blowing in the correct direction, temperatures of -5 degrees Celsius aloft and clouds filled with subfreezing water droplets – the generators southwest of Nevada’s Spring Mountains come to life. Burners ignite, sending skyward particles of silver iodide. As they rise into the clouds passing over the Pahrump Valley, those particles can act as what scientists call “ice-forming nuclei,” causing the suspended droplets to freeze into crystals, which are then able to grow into snowflakes big enough to tumble to earth in the nearby mountains.

Cloud-seeding may evoke science fiction, but as a technology it predates the jet age. American chemists and defence scientists began attempting to wring more moisture from the heavens soon after the end of the Second World War.

Now, drought has brought it back to the fore. In the Spring Mountains, local water authorities hope they can prove that cloud-seeding works well enough to provide a dependable new source of water.

Silver iodide particles

provide an additional

surface for cloud moisture

Advertisement

to freeze, causing ice

crystals to form at

high altitudes

-20 to -5˚C

Advertisement

cloud region

The ice crystals

become large and

dense, falling as

Advertisement

snow, hail, or rain

depending on

conditions

Silver iodide is

Advertisement

released from

cloud-seeding

generators in

updrafts below

cloud base

Advertisement

john sopinski/the globe and mail, Source: desert research institute;

open snow; comptroller.texas.gov

Advertisement

Silver iodide particles

provide an additional

surface for cloud moisture

to freeze, causing ice

Advertisement

crystals to form at

high altitudes

-20 to -5˚C

cloud region

Advertisement

The ice crystals

become large and

dense, falling as

snow, hail, or rain

Advertisement

depending on

conditions

Silver iodide is

released from

Advertisement

cloud-seeding

generators in

updrafts below

cloud base

Advertisement

john sopinski/the globe and mail, Source: desert research institute;

open snow; comptroller.texas.gov

Advertisement

Silver iodide particles

provide an additional

surface for cloud moisture

to freeze, causing ice

crystals to form at

Advertisement

high altitudes

-20 to -5˚C

cloud region

Advertisement

The ice crystals

become large and

dense, falling as

snow, hail, or rain

depending on

Advertisement

conditions

Silver iodide is

released from

cloud-seeding

Advertisement

generators in

updrafts below

cloud base

john sopinski/the globe and mail, Source: desert research institute;

Advertisement

open snow; comptroller.texas.gov

Water scarcity threatens livability and livelihoods across the southwestern U.S., an area with a vital agricultural sector that is home to tens of millions. A drought contingency plan for states in the upper Colorado River basin – Colorado, New Mexico, Utah and Wyoming – lists weather modification as one of its three main responses to the rapidly declining water levels in key reservoirs such as Lake Mead.

The effectiveness of such efforts remains a matter of considerable debate – one scientist has ridiculed “ersatz” successes in the field, while Israel recently abandoned cloud seeding because of its poor results.

But it’s a technology that has crossed the globe: China, its most active practitioner, has boasted construction of a system to generate artificial rain and snow over an area four times the size of Quebec.

The four generators in the shadows of the Spring Mountains form a considerably smaller installation.

Elsewhere in the southwest, water authorities have overseen sophisticated programs to dramatically cut water use.

Nye County, where the Pahrump Valley is situated, has chosen a different path. It has set out to prove that cloud seeding works well enough that the county can be credited with finding a reliable new supply and ultimately secure permission to use more water.

“If this community is going to keep growing, we’re going to have to find more water,” says Dann Weeks, general manager of the Nye County Water District, which includes the Pahrump Valley.

The Pahrump Valley occupies a closed basin bereft of rivers to deliver water or carry it away. Instead, some of the precipitation that falls on the area’s fractured rocks percolates down into underground aquifers.

Underground water levels in some parts of the valley have fallen by nearly five metres since 2004, a source of anxiety in an area where life and livelihoods depend on 11,000 domestic wells. Water rights in the area have been issued for three times what can be sustainably used.

The county, with a population of 52,000, has few options to secure more. It cannot rely on hydroelectric dams. A water pipeline could not be built without regulatory resistance and great cost.

So the county’s board of commissioners agreed to spend US$260,000 to extract new water from the sky.

“This is a test program to see what kind of increase can be generated into our groundwater basin,” said Helene Williams, who chairs the county water district governing board.

Cloud seeding is “probably the quickest, easiest solution that any community can look to,” she said.

The Pahrump Valley has never been short on ambition. Natural springs in the area drew humans for thousands of years; settlers irrigated cotton fields on the arid flatlands before the valley bottom was carved into tens of thousands of lots in the 1970s by a Florida development corporation. It employed boiler-room hucksters to lure buyers with free slot machine spins. They made gilded promises of life in a desert “breadbasket” that would one day become the third-largest city in the state, complete with a golf course. The pitch: “This is going to be an oasis in the middle of the desert,” said Mr. Weeks, a former journalist.

“None of that ever happened.”

A half-century later, the unincorporated town of Pahrump has yet to crack the state’s top 10 population centres, although it has continued to grow. It’s the place where voters in 2018 elected brothel owner Dennis Hof to the state legislature with 63 per cent of the vote, despite Mr. Hof being dead. A casino stands where cotton was once ginned.

For its cloud-seeding program, the county turned to Nevada’s Desert Research Institute, which has worked in cloud seeding since the 1960s. At the institute, meteorologists work around the clock from November until the end of winter, monitoring local weather stations, satellite radar and computer models to determine the right time to initiate the generators.

Nevada, the driest state in the U.S., has dozens of mountain areas that could be cloud-seeded, said Frank McDonough, a scientist at the research institute, and a growing number of places desperate for water. Among them are rural areas dependent on irrigation, where water withdrawals are exceeding resupply.

“Some of these basins are hitting the point where they’re pulling more than they’re recharging,” he said.

Colorado, Wyoming and Utah all have active winter cloud-seeding programs, too (programs distinct from hail suppression that uses similar technology in places like southern Alberta). Utah, which spends US$5-million a year on cloud-seeding, boasts extracting five to 15 per cent more precipitation over seeded areas.

Last year, the state of Nevada agreed to provide US$1.2-million to the Desert Research Institute for two years of cloud-seeding work.

Cloud seeding, Mr. McDonough said, tends to yield “on the order of 10 per cent more precipitation seasonally.” A preliminary report he submitted to the Nye County last year, after its first winter in operation, showed that 156 hours of seeding in the first year of the program had secured an estimated 6,653 acre-feet (8.1 million square metres) of additional precipitation.

That’s equivalent to fully one-third of the total allowable water use in the Pahrump Valley basin – and a figure large enough to support a considerable increase in population.

“In a subdivision, for every acre-foot of water I can build three houses,” said Mr. Weeks, the Nye County water district general manager. With the cost of operating the program, that works out to less than $70 an acre-foot, a tenth the price in other parts of the state.

“You can’t find cheaper water,” he said.

But there is reason for skepticism.

Israel, too, was an early adopter of cloud seeding, although it abandoned its program after 38 years of operations when researchers found it increased precipitation by just 1.8 per cent.

Cloud seeding can show results in certain times and places, but many “projects around the world are carried out under the (essentially untested) assumption that the cloud-seeding method is efficacious,” said Michael Manton, an emeritus professor of mathematical sciences at Monash University in Australia who specializes in cloud physics.

Even after seven decades of operational cloud seeding, the scientific community remains deeply conflicted about how well it works. Arthur Rangno devoted part of his career as a research scientist at the University of Washington to questioning studies of the technology.

“The problem throughout this field’s murky history is this: ‘No one ever got a job saying cloud seeding doesn’t work,’” he said in an e-mail.

That is not to say that cloud-seeding is a chimera invented by the thirsty. Wintertime seeding, like that being used by Nye County, can produce a 2 to 3 per cent increase in precipitation, said William Cotton, a professor emeritus of meteorology at Colorado State University.

Studies that tracked an airplane scattering silver iodide particles through the right clouds have yielded “eye-catching” results, with a vivid radar signature as crystals form, said Bart Geerts, an atmospheric scientist at the University of Wyoming.

In perfect conditions, seeding can double the snowfall from a particular storm, he said. But such conditions are hard to find, and other storms will show no impact whatsoever. Assessing overall results requires “an average of wildly varying numbers,” he said.

Natural precipitation is fickle, too, making it difficult to assess whether higher snowfall in one area is due to technological intervention or merely the vagaries of weather. Prof. Geerts calls cloud seeding, despite its long history, “exploratory.”

Still, water in dry places is so costly that even a 1 per cent increase in snowfall can be economically attractive. Take the Pahrump Valley, where the alternative is a water pipeline that would cost well over $100-million.

Nye County set out to find new water, instead, and with cloud seeding “we did,” said Debra Strickland, who chairs the county’s board of commissioners.

“Now we have to prove it with the science.”

What the county hopes to do is deliver that proof to the Nevada Division of Water Resources, which determines how much water the county can withdraw. First, though, it will have to convince Adam Sullivan, the Nevada state engineer who is administrator of water resources division.

“It’s a real long shot,” he said in an interview. “I don’t see it as something that’s even on my horizon.”

Never before has the state considered whether it can credit weather modification with bringing more water. Mr. Sullivan is a hydrologist, and says the question goes beyond how much snow cloud-seeding can deliver. More importantly, it’s whether that snow can meaningfully help water supplies.

In Nevada, “the vast majority of snow up in the mountains either sublimates or it’s lost or consumed through evapotranspiration.” On average, just 5 per cent of snowfall recharges water supplies.

There are, Mr. Sullivan said, far more reliable ways to boost water supplies.

“If you’ve got the money, you’re probably better off investing in conservation – in ways that we know work,” he said. “Just use less and live within your means.”

But conservation has proven difficult even in the face of drought, not least in the Pahrump Valley, a deeply conservative rural area whose rules provide few constraints to water use. Per capita water use is nearly three times higher than it is in an hour’s drive away in Las Vegas, where water managers have used a combination of fines and incentives to dramatically cut use.

Not so in Nye County, which only recently launched a rebate program to encourage the adoption of low-flow toilets. Its budget: US$10,000, a fraction of the cloud-seeding budget.

Decorative ponds in the county cannot exceed 400 square feet, but “there’s no limitation on your swimming pool,” said Mr. Weeks. Lawns can be maintained at any size. “There are no restrictions,” Mr. Weeks said.

“Some people think that’s crazy,” he acknowledges. “Some people ask me, ‘why aren’t you doing something about that?’”

His response: “We’re working on it.”

Water and climate change: More from The Globe and Mail

Meet the young Canadian farmers adapting agriculture to climate change

To save Great Salt Lake, Utah explores radical options – and other water-starved states are taking notes

Dominican Republic’s cocoa farmers race to adapt to drying jungles

Scientists’ quests to save the all-American front lawn from climate change