Cloud seeding could help solve water shortage
Cloud seeding should not – as some would have us believe – be put in the same category as a ‘rain dance’. Many countries are having varying degrees of success with the technique to encourage the skies to open up.
The science of cloud seeding is not new. People been investigating ways of getting rain clouds to part with their moisture bounty for more than 50 years.
Alex Nazarov is principal scientific officer for Hydro Tasmania (Australia) and has been working mostly in the field of hydrology since 1979 – the past three years full-time with Hydro Tasmania.
“Successful cloud seeding needs a special ingredient – clouds,” he says. “More specifically, clouds with a large water vapor content and a low temperature.”
Hydro Tasmania has a 100-year history in power generation engineering and dam construction and has 29 hydropower stations and more than 50 large dams. Hence, good rainfall is paramount for its business. Its total generating capacity is 2568MW and its assets are valued at more than US$2 billion.
In the natural rain-making process warm, moist air rises into the atmosphere, begins to cool and forms droplets of water. Cloud droplets form around cloud nuclei – tiny particles of dust, salt, or soil that are constantly present in the atmosphere.
Cloud droplets then group together in to clouds (it takes millions of cloud droplets to form one raindrop), which can precipitate in one of two ways.
In higher temperatures, droplets in the clouds merge with countless other droplets and become heavy enough to fall as rain. In lower temperatures, the droplets form ice crystals. Other droplets freeze onto these ice crystals, which grow larger and heavier until gravity takes charge and they fall to the ground as rain, snow, or hail, depending on how much they have warmed in the process.
Cloud seeding is not as basic as it sounds – in fact, it’s a complex process. In the simplest terms, it means introducing other particles into a cloud to serve as cloud condensation nuclei and help in the formation of precipitation.
When considering the science of cloud seeding, many people visualise small aircraft flying through clouds dropping magic rain-making ‘bombs’. The process can involve aircraft, but these planes often have special burning flares attached to their wingtips that douse the cloud with hydroscopic particles of silver iodide or dry-ice pellets. Or the aircraft can spray the chemical from beneath their wings. This is the most expensive method of making rain but it can cover a wide area.
Another method is to fire large shells containing silver iodide from old anti-aircraft guns or rocket launchers – the current practice in many parts of China. Another alternative is to burn silver iodide flares on hilltops where convection currents in the air can carry the payload upwards. Moisture in clouds collects around the chemical particles until it is heavy enough to fall. Of course, using the best method to suit local weather patterns is crucial to success.
Nazarov says cloud seeding has several applications, including precipitation enhancement, reduction in hailstorm damage, fog dispersal and even firefighting. More than 30 countries including the United States, Australia, Morocco, Burkina Faso (West Africa), Thailand, Indonesia and China are using or trialing cloud seeding for a variety of reasons.
Most countries are investigating cloud seeding to help fill storages for irrigation, potable water supply and electricity generation, but there are other purposes.
China has several reasons for its cloud seeding activities. One is to fill its newly created US$25 billion Three Gorges Dam, said to be the biggest construction project in China since the Great Wall.
The dam is one-and-a-half miles (2.4km) wide and more than 600 feet (180m) high. It will create a reservoir nearly 400 miles (640km) long. Apart from allowing access six months of the year to large ocean-going freighters, which will be able to sail directly into the nation’s interior, the dam’s hydropower turbines are expected to generate enough electricity to equal 18 nuclear power plants.
Added to the electricity generation – which China needs desperately to keep pace with consumption and growth – the project is expected to help pacify the Yangzi River (the third-longest river in the world), which has claimed more than a million lives in the past 100 years through flooding.
Exactly how serious is China about wringing the most water out of its clouds? The country has created the Weather Modification Bureau and has more than 3000 weather modification programs in operation, with about 35,000 people – many of them peasant farmers – helping with its efforts. Beijing’s weather modification budget is about US$50 million a year.
China says it wants to create an additional 48 billion to 60 billion cubic meters of rain annually through artificial methods. Like many other parts of the world, it is experiencing rain shortfalls. Parts of North China were in drought in 1998, and Beijing got less than 80% of its usual rainfall last year.
On top of its drought-breaking efforts, China has another motivation for increased cloud seeding – that is, to encourage the world to look favorably on Beijing at the 2008 Olympic Games. The phrase ‘don’t rain on my parade’ is an apt one.
In 2000, Russia held huge celebrations to mark the 55th anniversary of the end of World War II. Chinese officials who attended the ceremony brought back news that Russia had deployed cloud seeding to induce rain before the event, thus ensuring a dry spectacle.
It should be noted that heavy rain is not typical in August when the 2008 Games will be held, but Chinese officials don’t want to leave things to chance.
Rain is also a good atmospheric cleanser, and Beijing officials hope a good dousing before the event will clear the air for athletes and show off a sparkling city to hundreds of millions of spectators around the world.
The city will call on a veritable arsenal of rockets, artillery and aircraft in an attempt to blast the clouds out of the sky through cloud seeding, according to one meteorologist.
The Chinese Government has enlisted 37,000 peasants who have at their disposal 7000 cannon and almost 5000 rocket launchers to coax more rain from clouds across China’s parched areas. The ‘rain army’ has been used successfully to water crops, break up damaging hailstorms and even put out forest fires. The remnants of a sandstorm that blew through Beijing was washed away with rain attributed to cloud seeding.
The State-run news agency Xinhua reports that cloud seeding created enough rain in the past five years to fill the Yellow River, the nation’s second-largest, four times over.
Between 2001 and 2005, nearly 3000 flights triggered 210 billion cubic meters of water over areas making up almost a third of China’s territory, a National Meteorological Bureau official told Xinhua. But establishing the effectiveness of cloud seeding is practically impossible, because no one can know how much rain would fall without it.
In its latest five-year plan, China’s meteorological office announced it wanted to produce more rain in the future, but not over Beijing in August 2008.