Farming the Atmosphere for Water

Beyond the astonishing bird’s nest featured at the recent Beijing Olympics was perhaps a more spectacular accomplishment: large-scaled cloud seeding. Chinese film and Olympic opening ceremony director Zhang Yimou cited rain as the largest threat to the opening ceremonies. To ensure a rain-free performance, 1104 rocket’s filled with silver iodide were fired into the smoggy skies of 21 sites surrounding Beijing. These rockets dispersed cloud cover and prompted rain to occur before the clouds could disturb the Olympic site. Baoding city, located southwest of Beijing, absorbed 100mm of rainfall during the opening ceremonies, effectively keeping the bird’s nest dry.

Cloud seeding is one of the oldest and simplest weather modification technologies that, after many years of unsuccessful attempts, have incurred a recent resurgence of research. Given the complexity of dynamic atmospheric changes, the results of cloud seeding are difficult to prove. This doesn’t seem to be discouraging China, however, which has set up The Beijing Weather Modification Office (a unit of the Beijing Meteorological Bureau ) that employs over 37,000 peasants that aid in rain production. In a water-deprived nation like China, every drop in the atmosphere goes a long way.

Cloud seeding operates on the water vapor within clouds. Water vapor is typically converted to water droplets through impurities known as condensation nuclei. What seeding does is inject impurities into the clouds that allow water vapors to coalesce on, creating droplets around the nuclei. Gravity can now pull these droplets from the sky to produce rain. Cloud seeding typically occurs with the injection of silver iodide or dry ice that is either fired in missiles from land, or dropped by air via small planes. It is important to note that seeding cannot make clouds but rather promotes rain production in existing clouds.

Beyond the drying of the skies employed during the opening ceremonies, cloud seeding has several other functions. It has been used to help put out forest fires, reduce hail that often attack crops, cool temperatures to reduce electricity loads, and promote rain for agriculture in drought-stricken land. With such potential benefits, it is not surprising that India and the United Arab Emirates are following China’s lead and employing cloud seeding tests. reports that scientists are predicting increased drought, flooding and forest fires due to global warming in the next two hundred years. Reduced freshwater and more intense droughts will encourage desertification that impacts the amount of vegetative density. With less vegetation, increased runoff will also instigate flooding. Already highly valued freshwater is on its way to becoming one of the world’s most precious resources.

What is promising about the nascent research on cloud seeding is that it can promote rainfall in drought-stricken land as well as reduce flooding by dispersing rainfall over a larger landmass. As weather-monitoring devices increase in precision and can more accurately predict and map the complex network of atmospheric changes, perhaps we will develop an acupunctural approach to fertilizing the atmosphere to cultivate water and reduce the environmental impacts of global warming. Without more research and understanding of our atmosphere, however, cloud seeding could do more harm than good.

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