Heavy snow hit Beijing on Monday night. Meteorological departments forecast that the snowy weather will last about four days. [Fu Zengka/CFP]

With weather modification no longer a strange concept to most Chinese, some experts think that the governments and people depend too much on the weather control.

Beijing's unusually heavy snow, which brought a traffic paralysis to the capital yesterday, again highlighted the controversial use of weather modification.

The snow fell amid lightning and thunder in the capital late Monday to early yesterday, making it the second snowfall in eight days.

"The occurrence was rather unusual for early November," said Sun Jisong, chief forecaster of the Beijing Meteorological Bureau.

An official from the capital weather modification office who refused to be identified told China Daily yesterday that the second snow in Beijing was also artificially induced but refused to reveal further information.

On Oct 31, the first snow in the capital city this winter was partly induced by 186 doses of silver iodide, a compound used in cloud seeding. More than 16 million tons of snow fell on the city, Zhang Qiang, director of the municipal weather modification office, said earlier.

Without advance notice, the weather manipulation led to another big mess yesterday in Beijing, with traffic and flight delays.

The snow brought traffic to a crawl in the morning rush hour. Municipal transport authorities used more than 6,000 tons of thawing agent to clear the roads to ease congestion.

The snow also caused a four-hour shutdown of the Beijing Capital International Airport, with nearly 200 flights cancelled.

Beijing's first artificially induced snow on Oct 31 also caused hundreds of flight delays and cancellations, triggering complaints from the public.

Data from the National Meteorological Center (NMC) suggested yesterday's snowfall in most downtown areas of the city exceeded 10 mm, the index for a snowstorm.

Haidian district in northwest Beijing recorded 18.5 mm of snowfall, the heaviest in the city, according to the NMC.

The NMC said on its website on Monday that the local weather departments are taking the opportunity to manipulate the weather with rain and snow induction, relieving the drought in the south and water shortage in the north.

"No one can tell how much weather manipulation will change the sky. Past experiments showed that it can bring about 10 percent to 20 percent of additional rain or snow," Xiao Gang, professor from the Institute of Atmospheric Physics in the Chinese Academy of Sciences, told China Daily.

"We should not depend too much on artificial measures to get rain or snow, because there are too many uncertainties up in the sky," Xiao said.

Heavy snow also swept other parts of North China yesterday, causing air travel delays and highway closures.

Taiyuan airport in Shanxi province was closed yesterday morning, leaving almost 1,000 passengers stranded.

All highways in Shanxi were closed, officials from the provincial transport bureau said. They gave no timetable for reopening as the snow was predicted to last till tomorrow.

Transport authorities in Hebei province had reopened sections of the Beijing-Shenyang and Tangshan-Tianjin highways by noon yesterday. Six other highways are still closed as of yesterday.

He Lifu, chief forecaster of the NMC, said yesterday that in the coming three days heavy snow will hit Inner Mongolia, Shaanxi, Shanxi, Hebei and Shandong with the temperature drop of as much as 20 C.

Shijiazhuang Meteorological Bureau in Hebei province issued a yellow alert for snowstorm yesterday morning, predicting that the highest temperature will be minus 1 C.

The strong cold air has trapped thousands of travelers on the road or at the airport due to the frozen streets and heavy fog in many cities.

More than 10,000 passengers had to stay in the Chengdu Shuangliu International Airport, which was shut down for more than 8 hours because of the dense fog. Another 200 flights were cancelled in Shanghai.