In an effort to understand the Asian dust storms hitting China, a research team headed by Prof. Zhang Xiaoye of the CAS Institute of Earth Environment launched two research projects in 2000 and 2001 with the financial support from CAS, the Ministry of Science and Technology, and the assistance from China Meteorological Administration, respectively. Recently, the scientists announced that their work has made encouraging progress.
With an objective to make clear the formative mechanism of the dust storms, and their relationship with climate change and the desertification, the team carried out studies by integrating network observations with the numerical simulations in 2001 and 2002, and analyzed the data of dust storms that has occurred since 1960 when complete dust storm reports on the basis of visibility observations were started in China. The work leads to the most comprehensive data set of crucial materials ever obtained from hyper-arid, semi-arid, urban and rural areas of China during such a long periods, (including parameterization and validation of its numerical simulation). Besides, it achieves substantial progress in locating the sources of Asian dust storms, the overriding factors for its formative course, transport paths and heights.
On the basis of studies on the dust aerosol emission flux, scientists have found the dust storms coming from 10 major source areas, including the sources beyond Chinese boundaries, which contribute about 40% of the total Asian dust ejection, says Prof. Zhang.
After a subsidence lasting nearly 20 years, the sandy dust from Mongolia and northern China has eye-witnessed another rise in recent three years, which may mean the advent of another 20-year-long peak period in the Asian dust storm' s evolution.
The researchers believe that all the past and current evidence available suggests that, instead of the factor of desertification, the climate factors can also be held responsible for the mounting aggravation and increased occurrence of the dust storms both in Asia and China. Among the influencing factors in climate, the wind speed on the ground surface at the source regions seem to play a critical role in the damage caused by the storm.
Scientists told reporter that it is possible for some desertified regions, those areas with 200-400 mm in annual precipitation in particular, to resume their original appearance of arid steppes. However, as for the possible influence of the rehabilitation of desert-invaded lands on China' s big cities, especially on Beijing, an detailed and in-depth study is under way.
Through air-mass back-trajectories analyses of dusty days in 2001, the researchers have located five main transport paths for the redelivery of the sandy dust and the impact on Chinese cities, in particular on Beijing. One of the key and effective countermeasures to reduce the wind speed and associated dust storms, suggests the team, maybe the construction of wind-driven power plants at these passageways and at the mountain passes.
Their studies on the spatial distribution of the Asian dust storm show that the peak value of the dust-laden aerosol concentration in the vicinity of a source area is located less than 1,000 meters in elevation. The peak value is somewhere between 1,000 and 3,000 meters above the sea level in Beijing, Xi' an and other major Chinese cities of this sort. At present, the major measure against sandstorm adopted by China is afforestation, like wind break forests to be planted at the municipal periphery of Beijing. Scientists think people should be prudent to act in this regard because it is unclear whether it will be effective in preventing the occurrence of the storms, which passes by at a high elevation.
