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In addition, hail and heavy fog occur frequently. Official statistics estimate that abnormal meteorological phenomenon have incurred more than 70 percent of all losses caused by natural disasters.
As early as in the 17th century, Chinese people attempted to suppress hail by firing gunpowder from cannons into yellow clouds floating from mountains during the months of May and June, for such clouds were believed to carry hail, according to Yu.
The first successful cloud seeding operation in China took place in 1958 when a plane was used to spread dry ice into clouds to quench a severe drought in northeastern Jilin Province. Thereafter, weather modification technology has developed fast in the country.
During the 2008 Summer Olympic Games in Beijing, weather modification technology was used to deliver a rain-free opening ceremony on August 8.
Historical data indicated a 41-percent possibility of precipitation on that date in Beijing. To prevent rain from ruining the ceremony, the Beijing Meteorological Bureau set up 26 weather control stations in Beijing's vicinity, hired 32,000 people, and deployed aircraft, rockets and artillery to spread silver iodide crystals and dry ice in clouds 50 km upwind of Beijing, according to the Xinhua News Agency.
Finally, rain-bearing clouds were eliminated before reaching the Bird's Nest, the nickname for the roofless National Stadium, where the Olympic opening ceremony was staged.
Cloud seeding has also been used before major events to induce a cheerful mood among the population. Beijing was shrouded in cloud and smog in the three days before October 1, 2009, the 60th anniversary of the founding of the People's Republic of China when a grand military review was scheduled. The weather was depressing. Artificial rain was made in Beijing and neighboring provinces, then on the anniversary day, the parade was held under an exceptionally clear sky.
"Since rain cannot be created from nowhere, accurate weather forecasts and understanding of the clouds' conditions are required for successful weather modification. Meteorological equipment such as digital radar and microwave radiometer is needed," Yu said.
China has made steady progress in weather modification technology in the past decades, yet it still lags behind leading countries in the field.
Yu said that so far, the country still imports a significant portion of equipment, and Chinese engineers would like to develop its own advanced equipment to reduce the technology gap between China and leading countries.
With the rising use of weather modification, people are concerned with whether the catalysts added to the clouds will do harm to the environment. Zheng said that the environmental impacts of weather modification are negligible, adding that some of the most common catalysts such as dry ice and liquid nitrogen are naturally present in the air and are not at all harmful.
"Even though silver iodide is used to seed cloud, every shell only contains 1 gram of the chemical, so less than 1 ton of silver iodide is used in a year over a total area of about 5 million square km," Zheng said.
Artificial rain making has been carried out frequently near Miyun Reservoir, a major drinking water source in suburban Beijing. The office in charge of weather modification under the Beijing Metrological Bureau analyzed the silver iodide level in Beijing's rainwater and found it too far below the national standard and the standard set by the World Health Organization.
As to whether such operations may impact the global climate, Wang said that the impacts of weather modification are local and limited, and are not powerful enough to change climate.
"Artificial precipitation enhancement can only be carried out under the right weather conditions, and may increase the amount of rainfall or snowfall by 15 to 25 percent," he said.
Some scientists remain highly skeptical of the effectiveness of weather modification in increasing rainfall. A meteorologist who refused to be named told Caixin.com, a leading Chinese business news website, "The present technology is incapable of ensuring how much artificial rainfall will be produced. In addition to this, it could be a huge waste of resources if rainfall can't be consistently maintained."
Wang said that the cost-benefit ratio of artificial precipitation enhancement is usually around 1:20, and the ratio may vary depending on the type of crop to be protected from drought.
Zhang Peiqun, a researcher with the National Climate Center under the CMA, believes that weather modification is humanity's way of fine-tuning nature to our own advantage. "Without weather modification, rain might fall in a place without cultivated land or without pressing need for water, whereas with weather modification, clouds can be made to rain over cultivated land that thirsts for rainwater."
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