The sandstorms that have swept across China over the past two weeks are the result of strong and frequent cold spells rather than desertification, according to leading meteorologists.

In contrast to widespread opinion, the number of yellow and dusty days has actually decreased overall since the 1980s, they said.

Since March 11, the country was hit by five sandstorms over 12 days.

The most serious one occurred between March 19 and 21, when most of the country was bathed in dusty air, except Northeast China, Southwest China and the western part of the area to the south of the Yangtze River.

"Beijing had two sandstorms in three days! Even though all of the windows were shut tight, you could still smell a bit of dirt in the air," Beijinger Fang Fang said.

The occurrence of five sandstorms in March is the average level, said Zhang Peiqun, director of the climate service department of the National Climate Center (NCC).

According to NCC records, an average of four to five sandstorms have occurred annually in March since 2000.

"What impressed people most is that five sandstorms shrouded the country in such a short time," Zhang said.

According to Zhang, the first sandstorm this year came later than usual - in fact, the latest since 2001 - because the weather in Northwest China and Inner Mongolia had remained cold until mid-March.

"When the weather was cold, the dust was frozen to the ground, but as temperatures began to rise in mid-March, the soil thawed. In days with gales, it can easily produce floating dust and even form sandstorms," he said.

Meteorologists have observed rapid developing cyclones in Mongolia near the deserts that are the sources of the past five sandstorms.

The deserts, including the Gobi in southern Mongolia, western China and northern China, are all major contributors to sandstorms in Asia.

"A cyclone rolls dust into a high altitude. Strong cold waves then produced high winds that blew the sands to the east and to the south," said He Lifu, chief forecaster from the National Meteorological Center.

The phenomenon, coupled with the wind direction, accounts for why the sandstorm on Saturday affected such a wide area, including Macao and Hong Kong, he said.

China News Agency cited the latest forecast by the NCC as saying that, due to strong cold spells, northern China may expect another six to nine sandstorms in April and May.

However, meteorologists stressed that desertification should not be blamed for the recent storms, since the environment has been improving in northern China.

Citing satellite monitoring results, Fang Xiang, director of the remote sensing service of the National Satellite Meteorological Center, said the environment in northern China has not deteriorated due to the country's continual efforts to expand forestation and control sand.

Starting from the mid- 1980s, dusty weather in China has generally been declining, according to meteorological records.

Supporting the data, Fang said: "While an average of 18 to 19 sandstorms occurred annually between 1971 and 2000, only an average of 12 to 13 sandstorms happened each year since the year 2000."