Abu Dhabi, capital of the United Arab Emirates, is known for its extreme heat and aridness, which is why locals were extremely grateful — and awfully surprised — when it rained 52 times over two months last summer in the surrounding desert.
The highly unusual downpours — replete with hail, lightning and powerful winds — blew through eastern Abu Dhabi in July and August 2010, soaking desert flora that typically survives on the morning dew.
But the rain was neither a freak accident of nature nor the result of global warming, scientists say. It stemmed from a program, funded by the UAE, aimed at increasing rainfall in the water-poor Middle East to create more arable land and fresh water.
As part of the multimillion-dollar project, scientists set up devices in the desert called ionizers that look like big steel lampshades. The ionizers produce negatively charged particles that attract dust, ever-present in the desert air. Hot air on the ground rises and pushes the particles up and away from the devices. When the particles reach the height where clouds tend to form, their negative charge attracts vaporized water molecules, forming small clouds. As an increasing number of particles make their way up, rain results. Because the clouds are full of charged particles, they tend to generate not only rain but also significant lightning and thunder.
Efforts to create rain in arid regions are not new. In the western United States, for example, scientists have for years been successfully “seeding” clouds — a process in which chemicals, including silver iodide and particles of carbon dioxide, or dry ice, are sprayed into clouds from the air or ground, acting as nuclei around which rain drops form.
“Most of the operational programs are being done in areas where water is scarce, like the western United States,” says Arlen Huggins, associate research scientist at the Desert Research Institute in Reno, Nev., and a cloud-seeding expert. “What they're looking for is additional water in their watersheds.”
California, Nevada, Idaho, Utah, Colorado and Wyoming all have winter cloud-seeding programs, Huggins says. There are summer programs in North Dakota, Kansas and Texas, but no projects east of these Great Plains states, mainly because the amount of precipitation in the eastern part of the country is usually sufficient to support agriculture and municipal water supplies.
“Of course, any of these wetter areas can still have droughts, but that's the worst time to decide to start cloud seeding because there is a lack of clouds, and the traditional methods of cloud seeding require clouds,” Huggins says.
Most of the seeding projects under way in the United States are sponsored by water agencies or power companies seeking increased water to generate electricity. These efforts, Huggins says, have often proved successful.
Cloud seeding in the United States is generally governed by state regulations, and projects must abide by clean-air and -water laws. If a project is done on federal land, an environmental assessment is typically required, taking into account impacts on land, vegetation and wildlife.
“To date, every assessment I'm aware of has indicated the [negative] environmental effects of cloud seeding are negligible or have no significant impact,” Huggins says.
There's plenty of water in the pool of a hotel in the Liwa Desert near Abu Dhabi. A new ionization program helps create summer rain in the bone-dry region. (AFP/Getty Images/Karim Sahib)
The ionizing technique used in Abu Dhabi is relatively new and, Huggins says, untested. Indeed, he says, ionizers have not yet been shown to do what scientists like those working on the Abu Dhabi project say they can — and their reported successes may be just happenstance.
“It's like a lot of the early experiments in cloud seeding,” he says. “You can still have an occasion where, by coincidence, you'll have rain. Without a pretty rigid scientific experiment, you may or may not have a scientific correlation” between the ionizers and the rainfall.
Huggins says it remains “way too early” to tell what the ionizers’ impact might be. “Published results of any of their experiments are almost nonexistent,” he says.
Or, as Time.com put it in a story about Abu Dhabi's efforts: “How controllable the weather can be is still in doubt, and the consequences of meddling with nature at this level are yet to be seen.”
Other countries do more cloud seeding than the United States. There are projects in Australia, Argentina, Greece, France, India and China, as well as in the Middle East, where the interest has been more recent.
China's program is the largest in the world, Huggins says. Famously, one such effort went awry. After seeding clouds over Beijing to ease a drought in 2009, temperatures plummeted unexpectedly. The result: snowfall in November, the earliest snow Beijing had seen in a decade. It fell for half the day, coating streets and delaying air travel.
This wouldn't have surprised Huggins, who says that in the United States cloud seeding has proved successful in creating winter snowfalls.
“That's primarily being done in the Western states in the mountainous areas,” he says. “The result of that would be increased runoffs in the reservoirs or streams.”
— Chanan Tigay