| Dust storm is a severe weather induced by a large-scale circulation or a synoptic system, under a given geographic environment or underlying surface condition. It mainly appears in deserts, or in the adjacent arid and semi-arid areas. The frequent occurrence of dust storms makes an indicator, an accelerator, and a catalyst of pastureland degradation and land desertification. It is also a major warning marker indicating the magnitude of ecological environment deterioration. In the global context, dust storms are mainly seen in Central Asia, North America, Central Africa, and Australia. China's dust storms, mostly appeared in the northwest and northern part of the country, constitute a part of the dust storm process in Central Asia. It also makes China one of regions in the world having the most occurrences of dust storms.Studying dust storms and associated disasters in a systematic manner is extremely important to understanding a range of other issues, including ecological environment reconstruction, sustainable development, disaster prevention and preparedness, and climate change. In this context, the paper makes a systematic review of the latest progresses achieved in studying the dust storms both at home and abroad, before defining the subjects and objectives for the study. Author studies the spatial and temporal distribution of dust storms in North China, and analyzes the major factors that have an impact on the occurrence and development of dust storms and associated interactions, based on the surface, remote sensing, and other selected data, and the results of numerical modeling. Author also discusses the mechanisms that contribute to the occurrence and development of dust storms and associated internal variations, and examines the approaches that may result in an improved numerical dust storm modeling. In addition, author unveils the disadvantages of the existing approaches and policies dealing with dust storm control, analyzes China's dust storm control system, and proposes new strategies for dust storm control and prevention. The study has produced the following main conclusions:1. Dust storm is a man-made disaster, an environmental disaster (ecological disaster), as well as a natural disaster. The northern part of China is notorious for the frequent attacks of large winds, especially in the spring, which creates the needed momentum for the generation and development of dust storms and associated intensity enhancement The long lasting droughts and vulnerable natural ecological environment, the vast sandy surface, and unique terrains have built up an environment desirable for breeding out dust storms. The increased population and irrational utilization of land and water resources has beefed up the occurrence of dust storms like adding insult to injury. As a result, human activities have become a major factor contributing to the frequent occurrence of dust storms. Apparently, dust storms and enhanced intensity are the combined results of climate elements (wind), environmental factors, and human activities.2. Southwest-northeast spatial distribution pattern. The northwest part of China is a major region featured with the frequent occurrence and development of dust storms, mostly in the southern part of Xinjiang, the northern part of Tibet, the middle and west part of Qinghai, the middle and west part of Inner Mongolia, Gansu, Ningxia, the northern part of Shan'xi, the northern part of Shanxi, the northern part of Hebei, and some part of Henan. In China, the years having the most or least occurrences of dust storms and the associated multi-year average have show a basically agreed distribution pattern in line with the affected regions, though different in magnitude.The regions having most occurrences of dust storms have registered an extended cycle from this November to the following June-July. The inter-annual variations can be grouped into three categories and two transitional belts. 14 provinces, municipalities, and autonomous regions have been hit hard by dust storms, with an affected area reaching 6.24 million square kilometers, or 65% of China's territories. Tibet, Xinjiang, Inner Mongolia, Gansu, Qinghai, and Ningxia are the hard-hit areas.In the last four or five decades, the northern part of China has witnessed a basically declining trend for dust storms, though with an ascending trend for four regions: the west part of northern Xinjiang, with Zhaosu as the center; the northwest part of Qinghai, with Mangyan as the core, the east part of Qinghai, with Xinghai as the kernel; and the middle part of Inner Mongolia, with Zhuri as the center. Recent years have witnessed an increasingly enhanced intensity of dust storms, though the frequency is on the down side.The desert areas in Inner Mongolia have a higher frequency of dust storm attacks, compared with pastureland and farming areas in the same region. Farming areas have a noticeably low occurrence of dust storms, with a large annual variation of dust storm attacks for the area mixed with fanning and animal raising activities, indicating that the frequency of dust storm attacks is affected by the ecological environment of underlying surface. Zhurihe is an area frequently attacked by dust storms in Inner Mongolia.3. Dust storm disasters in the northern part of China are the combined results of meteorological conditions, ecological environment, and human activities. Study shows that the number of days and duration of dust storms are well correlated with rainfall, temperature, vegetation coverage, and days of large winds in different seasons. Specifically, the number of days and the duration of dust storms are negatively correlated with rainfall and vegetation coverage, but positively correlated with the days of large winds and temperature. The correlation is most noticeable in the context of the rainfall of last summer and this spring, the vegetation coverage of last summer, and the temperature of this spring. Both rainfall and temperature bear on the occurrence and duration of dust storms by affecting vegetation coverage. The frequent occurrence of dust storms is mainly associated with the dry surface and reduced vegetation coverage caused by the sustained decrease of rainfall.Of the elements affecting the number of dust storm days in the spring and in a year, and the duration of annual dust storms, the cyclic variation of vegetation coverage is a major factor determining the frequency of dust storms, followed by the days of large winds and rainfall. Temperature has the least impact on the occurrence of dust storms, though it remains an element that cannot be ignored.The days of large winds and temperature constitute the momentum to blow up a dust storm, while vegetation coverage and rainfall makes an obstacle blocking the formation and transport of dust storms. Momentum is much weaker than the obstacle. In this context, momentum is an internal cause for the occurrence of dust storms. On the other hand, momentum is an external factor. It becomes a dominant factor in inducing a dust storm, and in beefing up the needed transport, when vegetation coverage and rainfall are reduced to such a threshold that it will trigger up the occurrence of a dust storm. It is apparent that the increase of vegetation coverage in arid and semi-arid areas and the restoration of ecological environment in the north offers a key to curbing the occurrence and development of dust storms.4. Dust origins affecting dust storms in China and associated tracks. China's dust storms have the sand and dust supply mainly from the Gobi deserts in Mongolia, though also picking up sand and dust when traveling through the deserts or sandy land in the northern part of China. The domestic sand and dust sources likewise contribute to the occurrence and development of dust storms in the country, though to a lesser degree. China's dust storms move mainly in three directions: west, northwest, and north.The dust storms affecting the Beijing area either travel along a northerly track, or a northwest track. When moving in the north direction, it travels in the following tracks: Wulanchabumeng and the west part of Xilinguolemeng in Inner Mongolia - Hunshandake Desert - Zhangjiakou - Beijing. In the northwest direction, it goes from the northeast part of Xinjiang to the northern part of Alashanmeng in Inner Mongolia, to the Hexi Corridor, and further to Helanshan Mount. where it diverts in the south and north, to Maowusu Desert and to Wulanbuhe Desert respectively, before heading for Baotou, Hohhot, Zhangjiakou, and Beijing. Beijing's dust storms are fed with a sand and dust supply mainly from the northeast part of Xinjiang, Alashan Plateau, E'erduosi, the northern slope of Yinshan, Hunshandake Desert, and Bashang Plateau. One has to improve the ecological environment of these areas in the first place, if attempting to ease the impacts of dust storms on North China.5. Land degradation and grassland desertification. The reduced vegetation coverage makes an indicator, an accelerator, and a catalyst for the occurrence and development of dust storms. The change of land use/cover patterns, and the reduced vegetation coverage caused by land degradation and desertification, has resulted in a compromised ecological security, which in turn becomes an indicator, an accelerator, and a catalyst for the occurrence and development of dust storms. Study results show that the change of land use/cover patterns and vegetation coverage is noticeably coupled with the variations of dust storm frequency and intensity. In this context, the fundamental approach of curbing dust storms has to be addressing the social causes that contribute to land degradation and reduced ecological safety in the first place, rather than controlling dust storms. One has to handle the relationship between the development and the ecological reconstruction in a proper manner.6. Comparative analysis of four dust emission scenarios. Comparison results show that the modeling made by Shao (1996), and Marticorena and Bergametti (1995) has produced a dust storm hit area that is noticeably larger than the observed one. The results derived from the modeling of Marticorena and Bergametti (1995), in particular, have an emission that is much higher than the observed one. On the contrary, the modeling results presented by Lu and Shao (1999) have shown an affected area noticeably smaller than the observed one. Shao (2001) has worked out a simulated emission area that is quite close to the real situation, with the prediction products basically in line with the observational data, indicating that the said dust emission scenario yields fine predictions for the occurrence and development of dust storms in China.7. Impacts of human activities on the desertification in North China. In the past several thousand years, especially in the contemporary time, the population boom has resulted in increased human activities, which in turn accelerates the desertification in the north. It has also become a major cause for the increasingly expanded desertification in the region. Human activities worsen the desertification in North China mainly by affecting water resources, vegetation, soil, and climate. 8. Establish a North China desertification control modality with industry as the key player, supported by the market mechanism and private sectors. Author proposes that at the present stage, China shall strengthen the collaborations between industry and government agencies, introducing the PPP mechanism in desertification control, so as to address a range of related issues, including fund shortage, outdated management modality, and low efficiency. To curb the desertification in an effective manner, the Chinese government shall turn itself into a service oriented government, formulating favorable policies on fund raising, ownership, and ecological compensation, and paving the way for the introduction of market mechanism. Efforts shall also be made to enhance the legislations on desertification control, define the terms of reference of government at all levels for the purpose, protect the control results by punishing the criminal act in the area, and keep up a long lasting public awareness raising and education campaign.
|
PDF Full Text Request