cloud seeeding:china controlling the weather

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In the­ lead-up to the 2008 Summer Olympics, the People's Republic of China garnered a lot of press for all its housecleaning efforts. The country made strides toward cleaning up pollution, revamping public transportation and generally tidying up the city of Beijing. After all, the event promised to be the biggest party of the year, with the entire world invited to tune in. Authorities deterred potential party crashers by making it harder to visit the city and, yes, even requiring the visiting Luchadores to carry permits for their trademark Mexican wrestling masks.
­If you've ever thrown a party, you too may have fretted over every detail concerning the evening. Will the guests think you're cheap if you don't use the good china? Will your kids be on their best behavior, or should you banish them to their rooms? Chinese officials faced similar worries heading into the summer games, only they took their micro planning to unheard of levels. See, the Aug. 8 opening ceremony happened to fall during a traditionally wet season for Beijing. To avoid any crimp in their plans, they decided to shoot down any cloud that looked as though it might try to enter the city uninvited.


That may sound extreme, but Chinese authorities didn't become such meteorological control freaks overnight. Chinese research into weather control dates back to 1958. Forty years later, the government-run Weather Modification Program launches thousands of specially designed rockets and artillery shells into the sky every year in an attempt to manipulate weather conditions.
Run by the Weather Modification Department, a division of the Chinese Academy of Meteorological Sciences, the program employs and trains 32,000 to 35,000 people across China, some of them farmers, who are paid to handle anti-aircraft guns and rocket launchers [source: Aiyar]. These heavy-duty weapons launch pellets containin­g silver iodide into clouds. Silver iodide is thought to concentrate moisture and cause rain, a process known as cloud seeding. China has invested heavily in this technology, using more than 12,000 anti-aircraft guns and rocket launchers in addition to about 30 planes [source: Aiyar].
With a population of more than 1.3 billion, China requires vast amounts of water. The government practices cloud seeding to try to produce rain for farmers, stave off drought, clear away air pollution and smog, fill water basins and, of course, produce a picture-perfect opening Olympic ceremony.
­Were Chinese authorities successful in keeping their atmospheric gatecrashers at bay? And how does cloud seeding actually work? Read on to find out.
Cloud Seeding Methods
The Beijing Weather Modification Office spent a lot of time researching how to prevent rain in the city during the Aug. 8 opening ceremony of the 2008 Summer Olympics. The government even guaranteed clear skies for the event -- a promise it managed to deliver on. The feat only took the launch of 1,104 rain dispersal rockets from 21 sites in the city to pull off [source: O'Neill.
Even in areas with very low humidity, there's at least some water in the sky and clouds. A rainstorm happens after moisture collects around naturally occurring particles in the air, causing the air to reach a level of saturation at which point it can no longer hold in that moisture. Cloud seeding essentially helps that process along, providing additional "nuclei" around which water condenses. These nuclei can be salts, calcium chloride, dry ice or silver iodide, which the Chinese use. Silver iodide is effective because its form is similar to ice crystals. Calcium chloride is often used in warm or tropical areas.
Northern China, where Beijing is located, doesn't receive much rain -- its rainfall levels are 35 percent below the world average, and some of its water supplies are significantly polluted. The area relies heavily on cloud seeding. Zhiang Qiang, who runs the Beijing Weather Modification Office, told the Asia Times that water levels in Beijing's water basins have increased up to 13 percent due to cloud seeding [source: Aiyar. Cloud seeding also has been used to cool Beijing on hot days.
There are three cloud seeding methods: static, dynamic and hygroscopic.
Static cloud seeding involves spreading a chemical like silver iodide into clouds. The silver iodide provides a crystal around which moisture can condense. The moisture is already present in the clouds, but silver iodide essentially makes rain clouds more effective at dispensing their water.
Dynamic cloud seeding aims to boost vertical air currents, which encourages more water to pass through the clouds, translating into more rain [source: Cotton. Up to 100 times more ice crystals are used in dynamic cloud seeding than in the static method. The process is considered more complex than static clouding seeding because it depends on a sequence of events working properly. Dr. William R. Cotton, a professor of atmospheric science at Colorado State University, and other researchers break down dynamic cloud seeding into 11 separate stages. An unexpected outcome in one stage could ruin the entire process, making the technique less dependable than static cloud seeding.
Hygroscopic cloud seeding disperses salts through flares or explosives in the lower portions of clouds. The salts grow in size as water joins with them. In his report on cloud seeding, Cotton says that hygroscopic cloud seeding holds much promise, but requires further research.
­China has a reputation for launching ambitious projects, from the Great Wall in ancient times­ to the highest railroad in the world, connecting Qinghai to Tibet. But is the investment in cloud seeding worth it, and can the government really make it rain whenever it sees the need? On the next page, we'll look at some of the criticism surrounding cloud seeding.