Sandstorms hitting north China have not increased in intensity or frequency since the 1950s, said Zhang Guocai, director of the National Meteorological Center. "Serious ones like today's have been quite rare in recent years," he added.

The unpleasant weather phenomenon began two weeks later this year than in previous years. The city was already affected by sandstorms during the New Year's Day holiday in 2001.

Not keeping with their regular timetable, the sandstorms fortunately did not hit Beijing during the two-week annual annual sessions of China's top legislative and political advisory bodies, which lasted until mid-March.

Windy and dusty weather is quite common in Beijing, and some people may have confused flying dust with sandstorms, said Liu Shu, a senior expert for sand control.

"The minute dust particles that sometimes float around do not necessarily constitute a sandstorm," he explained, "This dust mainly comes from infertile farm land and exposed pastures."

Sandstorms that do sometimes hit Beijing are usually moderate not severe, Liu said.

Dusty weather comes from the interaction of strong wind and existing sand blown off deserts and desertified grassland, which, in turn, is the result of excessive cultivation and grazing, said Zhang Guocai.

Though the reducing acreage of pasture land is the main reason for floating dust and sandstorms in north China, the weather is another deciding factor for their occurrence, frequency and intensity, Zhang said.

According to Zhang, stable weather conditions and the absence of strong winds explain the late arrival of dust storms this year, but other experts disagree.

Ma Wenyuan, an expert in counter-desertification studies, attributes the late coming sandstorms to the warm winter.

"Sandstorms used to arrive in north China in February, when cold winds met with an early spring thaw," he explained.

The past warm winter meant an early thaw, he said, "And there were no cold currents to produce dusty weather this February."

The strong wind that blew on March 15 and 16 brought the year's first dusty weather in north China, but the chill factor was not strong enough to cause a serious sandstorm, he added.

However, experts do not exclude the possibility that severe sandstorms will come again in April. "Actually, sandstorms cannot possibly be avoided as a 200,000-square-kilometer desert extends from Hebei Province to Inner Mongolia," said Ma.

Forestation is by far the most effective means to prevent or reduce their occurrence, say experts. China has a plan to curb desertification in ten years by reining in sands, planting trees, reclaiming more farming land and preserving pastures in north China.

Beijing has also decided to speed up construction of more "green screens" to fend off sands coming from the northwest. This year, the Chinese capital plans to green 24,300 hectares of its land, say sources from the municipal landscaping committee.

"By 2007, 50 percent of Beijing will be covered in plants and the per capita greenland will reach 50 square meters," says a Beijing landscaping official.

(Xinhua News Agency March 22, 2002)