For decades China has been a rainmaker for its northern regions, where winds from the Gobi desert leave farmers high and dry and coat the parched capital of 15 million people with frequent sand storms.

But the Weather Modification Office is charged with among other things, dousing the city with rain to get rid of pollution, sandstorms, hail and fires and getting water to arid areas.

Just last Thursday the office said it has opened the heavens by firing off 163 cigarette-sized sticks and seven rockets into the sky, bringing as much as 11.2 millimeters of water to a parched, dusty and polluted Beijing, in the heaviest rainfall so far this spring.

The United States started making rain in the 1950s, but later gave up because they could not work out whether the seeding produced more rain, Chan said. China now boasts it is the world's leading rainmaker.

It has created enough rain during the past five years to fill the Yellow River, China's second largest, four times over, Xinhua news agency says.

Between 2001 and 2005, nearly 3,000 flights triggered 210 billion cubic meters of water over an area making up nearly a third of China's territory, an official from the National Meteorological Bureau told Xinhua.

An army of more than 3,000 rainmakers have at their disposal 7,000 cannons and 4,687 rocket launchers to coax more rain from clouds across China.

Chan warns the science for cloud seeding is difficult to prove scientifically, because experts don't know how much rain would have fallen without it.

"The problem is you don't have two identical clouds, where you seed one and not seed the other to compare the result," he says.

But he adds, if you do want rain, you might as well try to get it.

The meteorological office has announced in the latest five-year plan it wants to produce more rain in the future.

And if all goes to plan, none of it will be falling when the Olympics will be held two years from now.