China recently held a rain reduction drill to ensure that the opening and closing ceremonies of the Beijing [Images] Olympic Games in 2008 will not be interrupted by rain.

Three planes carrying 30 technicians flew for about three hours within a 80 km-radius area about 8,000 meters high above Hohhot, capital city of north China's Inner Mongolia Autonomous Region, spreading silver iodide and 2,800 kg of diatomite into the clouds.

Although the clouds were not as thick as expected and other weather conditions were unfavourable, the drill still collected sufficient data, an official with the Inner Mongolia weather control office, Liu Xiaolin said.

The two types of catalyser help to absorb vapour in the cloud and prevent it from forming precipitation.

Apart from the commonly-used silver iodide, the environment-friendly diatomite, a kind of white or grey-coloured mineral, was for the first time used in rain reduction in China, and its effect is yet to be further studied, Liu was quoted as saying by Xinhua news agency.

Rain reduction only works in a small area, and it would fail in thick or large-scale clouds containing large amounts of water, he said.

The drill on Wednesday, overseen by weather authorities of Beijing and Inner Mongolia, was just part of the rain reduction program to be launched if needed next August, a month when Beijing is prone to rain.

In addition to rain blocking above the venue area, cloud seeding will be made between 15 km to 120 km away to induce rainfall before it moves to the site of the event.

Rockets would be fired to disperse clouds in case of thunderstorms and other weather conditions.