The harm of sandstorm to human beings

[Edit this paragraph] VI. Hazards of sandstorm weather

Sandstorm weather is a disastrous weather in northwest China and northern North China, which can cause houses to collapse, traffic power supply to be blocked or interrupted, fires, human and animal casualties and so on. It pollutes the natural environment, destroys the growth of crops and causes serious losses and great harm to the national economic construction and the safety of people's lives and property. The hazards of sandstorms mainly include the following aspects:

1, ecological environment deterioration

When sandstorms occur, dust and floating dust carried by strong winds are everywhere, and the number of people passing through areas with air turbidity, choking nose and eyes, respiratory tract and other diseases increases. For example,1A serious sandstorm occurred in Jinchang on May 5, 993. The dust content in outdoor air is 10 16 mm/cm3, and the dust content in indoor air is 80 mm/cm3, which is 40 times higher than the national standard for dust content in living quarters.

2. Production and life are affected.

A lot of dust carried by sandstorm weather blocked the sun, and the weather was gloomy, which led to the decrease of solar radiation. A few hours to ten hours of poor visibility can easily make people feel depressed and reduce the efficiency of work and study. In light cases, a large number of livestock can be infected with respiratory and gastrointestinal diseases, and in severe cases, a large number of "spring-deficient" livestock will die, and fertile soil, seeds and seedlings in farmland will be scraped away. Sandstorm will also aggravate the wind erosion and desertification of the surface soil, cover thick dust on the leaves of plants, affect normal photosynthesis and cause crop yield reduction.

3. Loss of life and property

1On May 5, 1993, severe sandstorms occurred in Jinchang, Wei Wu, Minqin, Baiyin and other cities in Gansu Province, affecting 2,535,500 mu of farmland, losing 42,800 trees, resulting in a direct economic loss of 236 million yuan, 50 people died and 0/53 people were seriously injured. On April 12, 2000, strong sandstorms occurred in Yongchang, Jinchang, Wei Wu and Minqin. According to incomplete statistics, the direct economic losses of Jinchang and Wei Wu alone amounted to15.34 million yuan.

4, traffic safety (plane, car and other traffic accidents)

Sandstorm weather often affects traffic safety, causing planes to fail to take off or land normally, and making cars and train carriages rupture, stop or derail.

[Edit this paragraph] VII. The cause of sandstorm

Sandstorms originate from soil wind erosion.

According to Xinhua News Agency, Lanzhou Electric Power Co., Ltd., with the efforts of experts from the Institute of Environment and Engineering in Cold and Arid Regions, Chinese Academy of Sciences, recently successfully completed a sandstorm wind tunnel simulation experiment specially designed to explore the mechanism of sandstorm initiation and propagation.

Experts found through experiments that soil wind erosion is the primary link in the occurrence and development of sandstorms. Wind is the most direct driving force of soil, among which the nature of airflow, the magnitude of wind speed and the related conditions of wind action in soil wind erosion are the most important factors. In addition, soil water content is also one of the important reasons that affect soil wind erosion.

This experiment also proves that plant measures are one of the effective methods to prevent and control sandstorms. Experts believe that plants usually affect wind erosion in three forms: dispersing certain wind momentum on the ground to reduce the transmission between airflow and dust; Stop the movement of soil, dust, etc.

In addition, through experiments, the researchers concluded that the occurrence of sandstorms is not only the product of specific natural environmental conditions, but also has a corresponding relationship with human activities. Man-made overgrazing, deforestation, industrial and mining traffic construction, especially man-made over-reclamation, destroyed the ground vegetation, disturbed the ground structure, formed a large area of sandy land, and directly accelerated the formation and development of sandstorms.

The culprit of sandstorm: atmospheric circulation

The brief scene of spring sandstorm in Beijing is just a weather process that has been experienced every year for two or three million years on the Loess Plateau, which stretches for about 300,000 square kilometers in the north of China. The difference is that the wind of the latter is stronger and the wind lasts longer (it can last for several days). The source of sandstorm is not the crossroads 50 meters away, but the desert and Gobi hundreds of kilometers away.

It's like God is playing an incredible game: he grabs the dust on the surface of deserts and Gobi in northwest China and Central Asia and throws it to the southeast, leaving a highland where the dust falls. This game started about 2.4 million years ago, and God is still enjoying it (in 2002, Nature published the latest research results of China scholars, pushing the start time to 22 million years ago).

In fact, the wind is God's hand that throws sand.

After the Indian plate moved northward and collided with the Eurasian plate, the Indian continental crust was inserted under the Asian continental crust to prop up the latter. As a result, the shallow sea of the Himalayas disappeared, the Himalayas began to form and gradually lifted, and the Qinghai-Tibet Plateau was also squeezed and lifted by the Indian plate. After this process lasted more than 60 million years, by about 2.4 million years ago, the height of the Qinghai-Tibet Plateau had exceeded 2,000 meters.

The great change of surface morphology directly changed the pattern of atmospheric circulation. Before that, Chinese mainland was occupied by shallow seas to the east, Siberia to the north and Himalayas to the south, and the Mediterranean Sea to the west also extended to a far place in central Asia, so most of the flat Chinese mainland could get enough moist air from the ocean, and the climate was warm and humid. Northwest China and Central Asia are mostly subtropical areas, and there are no large areas of deserts and Gobi.

However, the east-west Himalayan mountains stopped the warm and humid air mass in the Indian Ocean from moving northward. With the passage of time, the northwest of China has become more and more arid, gradually forming a large area of desert and Gobi. This is the birthplace of dust accumulated on the Loess Plateau. The huge Qinghai-Tibet Plateau just stands in the westerly belt of the northern hemisphere, and its height has been increasing for 2.4 million years. The width of the Qinghai-Tibet Plateau accounts for about one third of the westerly belt, which divides the surface of the westerly belt into two branches. The south branch flows eastward along the south side of the Himalayas, and the north branch flows eastward from the northeast edge of the Qinghai-Tibet Plateau. This kind of high-altitude airflow exists at an altitude of 3500-7000 meters all the year round and becomes the main driving force for carrying dust. At the same time, due to the uplift of the Qinghai-Tibet Plateau, the East Asian monsoon has also been strengthened. The winter wind blowing from northwest to southeast, together with westerly jet, formed the Loess Plateau in the north of China.

In the desert and Gobi in the northwest of China and the inland of Central Asia, the rocks here disintegrate into pieces faster than other places because of the drastic change of temperature. Geologists divide it into gravel (more than 2 mm), sand (2-0.05 mm), silt (0.05-0.005 mm) and clay (less than 0.005 mm) according to its diameter. Clay and sediment particles can be carried to an altitude of more than 3,500m, enter the westerly belt, be transported to the southeast by westerly jet, and gradually fall until the middle and lower reaches of the Yellow River.

For two or three million years, the process of transporting sand from northwest to southeast in this part of Asia has never stopped. A lot of sand falls in the area where the Loess Plateau is located, and even many mountains in North China, such as Wutai Mountain and Taihang Mountain, have loess accumulation at the top. Of course, the scouring effect of several large rivers and countless valleys in northern China, including the Yellow River, is just the opposite of the accumulation of loess. Otherwise, the loess plateau will not be like this, and the thickness will not exceed 409.93 meters. The North China Plain east of Taihang Mountain is also a subsidence area of sand, but it is a subsidence area, and at the same time many rivers have developed, so the falling sand is either washed away by the rivers or buried by the sediment brought by the rivers.

There are hundreds of records about rain soil, rain loess, rain yellow sand and rain haze in China ancient books. The earliest record of "rainy soil" can be traced back to 1 150 BC: the sky is yellow and foggy, and sand falls from the sky like rain. What is recorded here is actually a sandstorm.

The location of rainy soil is mainly in the Loess Plateau and its vicinity. The ancients regarded this kind of thing as a strange catastrophe phenomenon and thought it was a sign of "harmony between man and nature" It is recorded in the Natural History compiled by Zhang Hua in the Jin Dynasty: "When Xia Jie was in the deep valley, the night palace was mixed with men and women, and he did not go out to listen to politics for ten days. It was a windy day and filled the empty valley overnight. "

During the period of 1966- 1999, there were 60 sandstorms lasting more than two days in China. Academician Liu Dongsheng of the Chinese Academy of Sciences thinks that the Loess Plateau should be regarded as a laboratory for sandstorms, which has accumulated records of sandstorms for millions of years. Sandstorms from the northwest desert and Gobi are scattered all over the sky, leaving a thin layer of loess on the Loess Plateau every year.