Large-Scale Sandstorm Disasters--Their Causes and Prevention

　English　　Technical-paper

Large-Scale Sandstorm Disasters
--Their Causes and Prevention Measures

Vice-President of the Chinese Academy of Forestry Since the spring of 2000, Beijing and northwest China have experienced several sandstorms affecting a large area. The scope and intensity of these sandstorms were the worst since "muddy rain" resulted from sandstorm hitting Beijing in the spring of 1998. The sandstorms are now becoming more and more intense, covering about half of China from west to east and bringing about large-scale natural disasters across the territory. Characteristics of the Sandstorms In recent years, sandstorms have been occurring more frequently, with enhanced intensity and expanded scale. This is, to some degree, related to the frequent spells of unusual weather and the global climatic changes over the past century. However, the intensifying sandstorm threat has certain connections with land desertification. Distribution Characteristics of Severe Sandstorms in Different Areas: Northwest China is a region where severe sandstorms occur frequently and bring about serious damage. Two routes allow cold high pressure systems to initiate severe sandstorms. 1) The Western Route: Affected by anticyclones from Siberia and the Inner Mongolia Autonomous Region of China, the sandstorms on this route move rapidly, intensify quickly, have a wide influence and bring severe disasters. The route passes through: --The Tarim Basin and Tulu-Bishan-Toksun Basin, through Gansu Province to northern Shaanxi. The center of cold high pressure after the front is in the Xinjiang Uygur Autonomous Region or west of Inner Mongolia. --The Kalpin, Hotan, Minfeng and Geermu route in Xinjiang. Severe sandstorms continue for long periods in this area. --The route through Dunhuang and Minqin which moves eastward. 2) The Northern Route: Cold air goes southward from Lake Baikal through central Mongolia to northern Shaanxi Province, which influences the Inner Mongolia, Ordos and Alxa plateaus, Bayinmaodao and Yulin. Distribution Characteristics of Strong Sandstorms in Time Severe sandstorms started to occur frequently after the 13th century, and increased rapidly after the 18th century. The number of severe sandstorms grew rapidly after the founding of the People‘s Republic of China. There were five in the 1950s, eight in the 1960s, 13 in the 1970s, 14 in the 1980s and 20 in the 1990s. The frequency is rising. Severe and widespread sandstorms mainly occur in the period from March to May, especially in April. The Damages They Caused Severe sandstorms are major disasters in arid and semi-arid areas. They occur suddenly and affect large areas causing great losses to the national economy and the people. One example was an especially severe sandstorm on the Western Route, affected by cold air from Siberia. It moved quickly southward from May 4 to 6, 1993, affecting a total area of 1.1 million sq km, from northern Xinjiang to the Hexi area of Gansu, western Inner Mongolia and most of the Ningxia Hui Autonomous Region. The wind speed reached 37.9 m/s (greater than a Force 12 wind). The average wind speed was 21m/s (equal to a Force 8 wind), and the visibility was less than 50 m. The sandstorm caused great losses. In Xinjiang, Gansu, Inner Mongolia and Ningxia, 85 persons died and 264 were injured, 4,412 houses were destroyed, and 120,000 animals died or went missing. About 373,333 million hectares of crops were destroyed, over 2,000 km of ditches were buried, and transportation and telecommunications facilities were severed in some areas. The direct economic losses hit 550 million yuan, which further damaged the ecological environment and economic development. Another example is the sandstorm which raged from April 16 to 18, 1998. Blowing from west to east, it even reached the lower reaches of the Yangtze River. This was almost unprecedented in history. A severe sandstorm meeting rain over Beijing formed "muddy rain" there. In the city of Nanjing, Jiangsu Province, the suspended solids in the air were eight times the normal index. Floating dust afflicted the Inner Mongolia Autonomous Region, Beijing, Jinan of Shandong Province and Nanjing. Cause of Severe Sandstorms Severe sandstorms are caused by both natural and artificial factors, that is, climatic, geographical, social and human factors. Natural Factors in the Formation of Severe Sandstorms As mentioned above, the severe sandstorms in northwest China are closely related with the atmospheric, topographical and vegetation conditions. Sandstorms often occur in and mainly affect arid and semi-arid areas in the middle latitudes, which are also endangered by desertification. These areas are the most sensitive to global climate change and exert a negative effect on it. Landforms and landscapes play a leading role in the formation of sandstorms. In northwest China, mountains alternate with basins, and plateaus are connected with plains. For example, the Zhunge‘er Basin is located between the Tianshan and Altai mountains; and the Tarim Basin is situated between the Tianshan and Kunlunshan mountains. To the south of Gansu are the Qilianshan and Aerjin mountains, and to its north is the bulge region of the Alxa Plateau-Northern Mountains flatlands. The plain of Gansu is situated between them. The landforms, which may increase gradients of air pressure and temperature, play a leading and strengthening role in the formation of sandstorms. Sandstorms often take place in inland desert areas. The Taklimakan, Badanjilin and Tenggeli deserts often experience sandstorms. In arid and barren areas, large stretches of desertified land and sandy land provide rich sources for sandstorms. In areas under the protection of shelterbelts, sparse forests can protect an area 24-38 times that of the height of the trees, which can reduce the wind speed by 34 to 41 percent on average. The preventive force of shelterbelts is obvious. In 1961, for instance, an especially severe sandstorm hit Turpan County, in the Xinjiang Uygur Autonomous Region. The Force 12 wind lasted for 13 hours, sweeping 85 percent of the crops of the county. Over 6,700 hectare of wheat ready to be harvested, which had a per-unit output of only 4.5 kg, and 2,667 hectare of cotton and 4,000 hectare of sorghum were blown away. However, when the same sandstorms and extremely arid winds hit the area in April 1975, it underwent a much smaller disaster. After 1961, Turpan County put great efforts into building shelterbelts, planting grass to fix sand and constructing water conservancy projects. By 1975, 3,100 shelterbelts to protect farm land had been set up and 5,333 hectare of grassland had been constructed. Seventy percent of the farmland had been put under the protection of shelterbelts, and the ability to resist sandstorms was greatly improved. As a result, only 8 percent of the seeded areas were hit by sandstorm disasters. Here is another example: An especially severe sandstorm hit the Xinjiang Uygur Autonomous Region in 1998, causing an economic loss of over 900 million yuan. The Shihezi area, however, escaped damage from the worst sandstorm for 40 years, for it had put great efforts into afforestation and the vegetation coverage rate had reached 40 percent. Artificial factors in the formation of severe sandstorms Human activities play an important role in the formation of severe sandstorms. There are two main aspects: One is the improper use of land. An analysis by the United Nations Environment Program shows that of all the degraded land in general, 34.5 percent has been caused by over-grazing, 29.5 percent by the destruction of forests, 28.1 percent by the inappropriate use of agricultural land, and 7.95 percent resulted from improper use of water resources, industrial and mineral production and transportation. The situation in China is similar to this. The other factor is population growth and the rapid spread of urbanization, which increases pressure on productive land and will lead to short-sighted activities by peasants and herdsmen, who seek to improve their living standards by intensified economic activities. Major human activities affecting the climate are as follows: Excessive cultivation of farmland: Of the land opened up in the past 10 years, one half has already been abandoned. From 1986 to 1996, the National Agricultural Administration Office conducted a satellite remote-sensing survey covering 53 counties or county-level cities in Heilongjiang, Inner Mongolia, Gansu and Xinjiang. The result demonstrates severe grassland and forest destruction in those districts. In the 10 years, about 1.74 million hectare of land was cultivated, but only 884,000 hectare remained cultivated, accounting for 50.8 percent of the total. The three great waves of cultivation since the 1950s, destroyed large stretches of natural vegetation, which later further deteriorated into bare, sandy land. With neither conditions for cultivation nor protective measures, many areas became desertified. Deforestation: Because of excessive felling of trees, the ecosystem of the western regions has no vitality at all, except the drifting sand. The area of diversiform-leafed poplar forest along the lower reaches of the Tarim River has decreased by 75 percent--from 53,000 hectare in the 1960s to 1,333 hectare at present. The Bashang area of Hebei Province is a transition zone from grassland to forest. Due to over-cutting, the ecological environment has been seriously damaged. According to satellite-produced data, the area of forests here decreased by 38.82 percent from 363,500 hectare in 1987 to 222,400 hectare in 1996, while the area of drifting sand increased by 81 percent from 68,000 hectare to 129,100 hectare. Over-grazing: Over-grazing has led to serious grassland degeneration. Now 70 percent of the grassland in northwest China has been degraded. The overloading rate of livestock breeding is 50-120 percent, and as high as 300 percent in some areas. Excessive use of water resources: Water resources in the arid and semi-arid areas of northwest China mainly come from rainfall, surface runoff and underground water. For many years, there has been great waste in the use of water resources due to lack of scientific management. Also, excessive irrigation is found on the upper reaches of rivers. Serious water shortages and uneven distribution of water resources have caused difficulties in water use, and the death of natural desert forest and vegetation in northwest China. Measures and Suggestions Large areas subject to severe sandstorms in the arid and semi-arid areas of northwest China are characterized by great economic losses and ecological disasters. This is the result of expanding desertification. Consequently, the priority task in controlling sandstorms should be to combat desertification. The following are some suggestions: First, it is suggested that certain administrative methods be taken to turn desertification prevention into the record to evaluate the work of local government officials. Second, the issue of desertification prevention should be included in the national economic and social development program for the 21st century, and it should be on the list of key national projects and items of infrastructure construction. Third, The prevention plans must be drawn up scientifically, and the management must be strict. Desertification prevention is a systematic project. Enough attention, therefore, should be paid to ecological construction while harnessing desertified areas. Seriously desertified areas give rise to sandstorms. Measures should be taken to accelerate the speed of the planting of vegetation in areas without grass or tree coverage. Fourth, importance should be attached to experts‘ participation in the project, and the building of a new type of structure which combines production, scientific research and promotion under the new circumstances. As desertification prevention is the project involving great difficulty and many aspects, it is suggested that scientific studies be pursued in combination with practical efforts, and 3-5 percent of the basic fund be abstracted from the development fund to support scientific studies and improve construction quality. At the same time, new technology, experiences and theories from abroad can be adapted to meet our own needs. Fifth, we must do a good job of monitoring and forecasting desertification. We must also establish an information network for national desertification and sandstorm prevention, with forecasting work focused on controlling desertification at the beginning stage. Sixth, we must enhance international cooperation and exchanges. This is important because both desertification and sandstorm prevention touch upon the international environment. While expanding the influence of China, we should try every possible means to enlist international aid in capital and technology so as to promote the overall project of desertification prevention.

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