Around the world and across the centuries, people have tried to coax more rain from the heavens, through rituals like sacrifices or rain dances or prayer. Rainmaking has become more scientific in the last 50 years,and somewhat more successful, through "cloud seeding." These modern rainmakers send microscopic particles into the air expecting that moisture in the clouds will concentrate around them, then grow heavy enough to fall as rain or snow. This technique can sometimes reduce the intensity of a hailstorm, and it can increase the precipitation that a passing cloud delivers, so many countries are experimenting with cloud seeding.
It's hard to miss Paul DeMott's wind tunnel facility as you came toward the laboratory. It towers above his cloud seeding laboratory at Colorado State University in Fort Collins.
Of course, the equipment inside the lab is just as impressive: there are two metal chambers, each the size of a small truck, designed to create clouds then supercool them to mimic conditions over the mountains. What look like hand-held rocket launchers stand along one wall, ready to blast out flares full of gunpowder and silver iodide, the cloud-seeders' "magic bullets." The giant wind tunnel, which is wide enough to hold a dozen people, allows researchers to monitor how air currents affect cloud formation. To show off his 15-meter-high tunnel, Mr. DeMott invites me to join him as he climbs a very steep ladder.
While I clutch the ladder, knees shaking, Mr. DeMott zips through a trap door to the roof of his lab, revealing the top of the wind tunnel, plus a spectacular view of the snow-covered Rocky Mountains, about 80 kilometers away. He says clouds passing over those craggy heights are a dream come true for cloud seeders.
"There's very often excess cloud water flowing over the tops of mountains. It covers structures close to the peaks. You can see it," he said. "It freezes onto structures. And I know if you were to point a generator making these types of nuclei from silver iodide into that region, it would turn a lot of that water into ice, and if conditions were right, you would get it on the ground."
Getting moisture to the ground is the focus of people concerned about changing weather patterns. At Paul DeMott's lab, climatologists study how wind-born dust from deserts in China generates rain-making clouds in Colorado by attracting moisture as they're blown across the Pacific. In some experiments, these scientists actually use Chinese desert dust, but their more common rainmaking potion is silver iodide, a butter-yellow powder that attracts water droplets.
Man-made rain is getting more attention in Colorado, because the state is facing its most severe drought in over a century. A lack of snow last year meant half-empty reservoirs and a tough winter season for ski resorts. On Colorado's slopes this year, skiers are happier with the snow conditions.
"It's wonderful, it's powdery, it's soft. It's perfect. Perfect. I like it," said a woman skier. "Very soft, there was no ice out there. Packed powder. No complaints," adds a male skier. "There's snow and I can ski," said a child.
Most of this season's snow is thanks to Mother Nature. Most, but not all. This winter resort also creates snow by blasting air and water through a pressurized hose, a costly method that's often criticized for pulling water from already low reservoirs. Then there's cloud seeding, which, according to some experts, boosts natural snowfall by 15 percent.
"So here we are, sliding down a catwalk in Beaver Creek, Colorado, on some of our generated snow from our snow makers in the heavens," said Jimmy Roberts, director of operations for Beaver Creek Ski Resort, which accommodates 10,000 skiers a day.
To view those cloud seeding devices, I ski alongside Mr. Roberts. We dodge a group of snowboarders, then head for a stationary cloud seeding generator managed by Western Weather Consultants. When people first hear about cloud seeding, they often envision an airplane, zooming through the sky, trailing a mist of rainmaking chemicals. In reality, most cloud-seeding generators are ground-based because they're cheaper and safer. I'm hoping they'll still be dramatic, for instance, shooting silver iodide flares from a giant cannon. So I eagerly wait for the Western Weather technician to buzz in on his snowmobile.
He swaggers through the snow to a waist-high metal barrel topped by a small but ominous looking metal ignition chamber. Next, he reaches for the switch that will ignite the propane from a nearby tank, and flips it.
The ski resort's cloud seeding generator is just a big trashcan that burns silver iodide in a golden orange flame.
"The flame's about a foot tall, and it's just burning the solution in the flame, and once it's ignited, it carries it off into the atmosphere, using the wind currents and the heat from the flame," explained a technician.
There are fancier cloud seeding generators, but they all operate basically this way. Western Weather Consultants has positioned roughly 50 computer-monitored generators throughout this valley. They can be fired into action at just the right moment to squeeze an extra 10 to 20 percent of moisture from passing clouds.
Some people worry that cloud seeding might pollute the atmosphere with silver iodide, or 'steal' rain from another community downwind.
But back at his lab in Fort Collins, Professor DeMott dismisses those concerns. He says that cloud seeding is practiced in so few places worldwide, there's not enough of the chemical to affect the environment. And he explains that since clouds are like an enormous sponge, seeding affects just one tiny piece of them.
"You're squeezing out the very tip of the corner of the sponge, but the atmosphere is a tremendous reserve for moisture compared to what you're doing, and the little hole you might have created over that local little area is easily filled by moisture from the atmosphere," said Mr. DeMott.
While ski resorts have worked with cloud seeding experts for decades, this year, many Colorado water districts are also turning to those 'magic bullets,' according to the manager of Denver Water, Chips Barry.
"Denver Water's undertaking cloud seeding operations for the first time since 1977, because the current drought is worse than any drought on record, and the only cure for a drought is precipitation," he said.
It's an expensive cure. Denver Water's cloud seeding efforts could cost up to $700,000, if there are clouds worth seeding. after all, you can't seed a blue sky. They'll continue through March, in hopes of boosting spring snow that will feed reservoirs throughout the summer. But Mr. Barry says his water district will stop using this method once the current drought is over.
"I don't think we ought to be doing it every year, because I don't want to become reliant on it. But in a year like this, we need to do everything we can do, and cloud seeding falls into that category," he explained.
There are no guarantees, but if the cloud-seeders can increase snowfall by 10 to 15 percent, as most experts predict, Mr. Barry says the water produced artificially will cost 80 percent less than water bought on the open market.
