Beijing is preparing to manipulate the weather to ensure that it does not rain on its National Day parade on Oct 1.

Zhang Qiang, deputy director of the Beijing Weather Modification Office, told China Daily that "artificial rain reduction" measures were in place for the National Day celebration, during which President Hu Jintao will give a speech and the military will parade past the Tian'anmen Square.

Similar moves were taken during the Beijing Olympic Games last year, when meteorological workers fired 1,104 rain dispersal rockets from 21 sites in the capital on the eve of the opening ceremony, which prevented a rain belt from moving toward the stadium.

"From weather records for the National Day in Beijing in the past three decades, we see a 30 percent chance of rainfall, mostly drizzle," Guo Hu, head of the Beijing meteorological bureau (BMB), told China Daily.

The weather modification office will only attempt to modify the weather if it forecasts rain in the days leading up to Oct 1.

Zhang said that experience shows that artificial rain reduction can influence regional weather, like the successful experiences in dispersing rain clouds during the Olympic Games, but it cannot prevent large-scale weather trends.

He did not provide details on the rain reduction measures planned for the National Day parade, which will mark the 60th anniversary of the founding of the People's Republic of China.

Despite the weather modification success during the Games, experts have felt uncertain about technologically preventing rain.

Ye Qian, assistant president of the Chinese Academy of Meteorological Sciences, said Monday that humans haven't found an effective way to change weather.

"Artificial rain reduction is like boiling water. If you want to stop the boiling, you must turn off the fire before it reaches the boiling point. But we just cannot find the point," Ye said.

The common way for artificial rain reduction is cloud seeding -- dispersing substances like silver iodide into the air to alter the microphysical processes within the cloud. The chemical can cause temporary incapacitation or possible residual injury to humans and mammals if intensively exposed.

But the amount used in rain reduction is small, which causes no harm to the environment or humans, Ye said.

The United Nations Environment Program said on its website that there are no expected environmental effects associated with cloud seeding, except some limited harm caused by the chemicals.

The bureau records show that the average temperature on Oct 1 ranges from 16 C to 23 C and the average wind speed is 2 m per second, which is suitable for outdoor celebrations.

(China Daily August 25, 2009)