Causes, harm and control measures of desertification in northwest China

In spring, the temperature warms up, the earth thaws, the ground soil becomes loose, the ground temperature gradually rises, and the vertical airflow increases. If there is a strong wind in the north, dust will be blown high into the air. Sandstorm will form ~ Sandstorm is a disastrous weather phenomenon with sand-wind interaction, and its formation is closely related to global greenhouse effect, El Nino phenomenon, forest decline, vegetation destruction, species extinction, climate anomaly and other factors. Among them, excessive exploitation of natural resources, excessive deforestation and excessive land reclamation caused by population expansion are the main reasons for frequent sandstorms.

As a kind of high-intensity sandstorm disaster, sandstorm can't happen in all windy places, but only in those areas with dry climate and sparse vegetation. In the northwest of China, the forest coverage rate is not high, and the poor in the northwest want to get rich by digging licorice, holding seaweed and mining. These predatory acts of destruction further aggravated the sandstorm disaster in this area. Exposed land is easily rolled up by strong winds, forming sandstorms or even strong sandstorms.

After a large-scale sandstorm occurred in late winter and early spring, the dust raised by strong winds caused a lot of dust in the air, which blocked the local sunshine and even made the visibility zero. Therefore, super sandstorms are also called black storms. Sandstorm will cause great losses to people's lives, property and agriculture. Sandstorms mainly originate in desertification areas, with soft soil, dry ground and no vegetation. Once the air is unstable in a large range and the surface wind speed is high, it is easy to blow up the surface dust and enter the air to form dusty weather.

After the occurrence of sandstorm, the larger dust particles are mostly behind the influence source or adjacent areas; That is, smaller particles can be transported upward to an altitude of 1000 to 3000m, and then transported eastward by the airflow in the westerlies. In the process of transportation, some dust is diffused or diluted, which makes the dust farther and farther along with the transportation distance; The lower the concentration, the ground will be reached under the action of settlement or rainfall (snow) during the transmission. Dust in the northwest of China can move eastward to Japan, South Korea and Hawaii, which is 10000 km away, and southward to Taiwan Province Province, Hongkong and even the Philippines, with a wide range of influence.

After the sandstorm spread to other areas thousands of kilometers away, the local visibility and suspended particles in the atmosphere increased, which affected the air quality there. As for the time or scope affected by sandstorm, it depends on the scale and duration of sandstorm in the source area and whether the meteorological conditions in remote areas are conducive to sandstorm transportation. According to the observation records, the visibility is affected for a few hours, and it is as long as a week, even causing mud rain.

Dust weather is divided into three categories: floating dust, sand blowing and sandstorm:

Floating dust: a weather phenomenon in which sand or soil particles suspended in the atmosphere make the horizontal visibility less than 10 km;

Sand blowing: the wind blows up the dust on the ground, making the air quite turbid, and the horizontal visibility is within 1- 10 km;

Sandstorm: a weather phenomenon in which strong winds blow up dust on the ground, making the air very turbid and the horizontal visibility is less than 1 km; When the horizontal visibility is less than 500 meters, it is a strong sandstorm.

According to the research, sand dust in desert area is the main source of suspended particulate matter on the earth, and sand dust in Sahara desert alone accounts for 25% of suspended particulate matter in the global atmosphere. Northwest China is located in the desert area of Central Asia, ranking second among the four desert areas in the world (Central Africa, Central Asia, North America and Australia in turn), so the impact of dust in the northwest on the atmospheric environment in East Asia can not be ignored. The conditions for the occurrence of sandstorms are:

Surface characteristics: soft and dry soil, no vegetation or vegetation growth, no snow.

Meteorological conditions: the ground wind is strong and continuous, and the meteorological conditions are vertically unstable, with no rainfall and snowfall.

The total area of desert in northwest China is nearly 600,000 square kilometers. The main source areas are located in northwest China, north China and Mongolia, including Xinjiang, Gansu, Hetao, Inner Mongolia and Mongolia, north of 35 degrees north latitude and west of 125 degrees east longitude. The annual rainfall in this area is below 400 mm, and the seasonal distribution is quite uneven, which is the main source of sandstorm weather in East Asia. Late winter and spring are the main seasons for sandstorms, with the highest frequency from March to May, accounting for more than 60% of the whole year, and the number of sandstorms varies from year to year.

Mongolia is the main foreign dust source that affects most parts of North China, especially Beijing. The external dust sources that affect the dust weather in northern China are mainly located in the desertification areas of Kazakhstan and Russia.

Mongolian vortex system is the main factor affecting the dust weather in eastern China. After the formation of the Mongolian vortex, the local dust is generally rolled up and gradually moved south. In the process of moving, the updraft at the tail of the vortex will drag the dust from the dust source along the way into the vortex and transport it downstream. Beijing is in the downwind zone, and the deep vortex system often brings dusty weather to Beijing.

There are two main moving paths that affect the dusty weather in Beijing: the North Road starts from the eastern and western regions of Mongolia and passes through Hunshandake Desert, Huade and Zhangjiakou in western Inner Mongolia to Beijing; West Road starts from Hami City, Gansu Province, reaches the border between China and Mongolia in Alashan League, Inner Mongolia, along Hexi Corridor, south foot of Helan Mountain, passes through Mu Us Desert and Wulanbuhe Desert, Hohhot City and Zhangjiakou, and finally reaches Beijing. Sandstorms that occur on the edge of Taklimakan Desert in Xinjiang will form long-distance transportation when encountering strong transit systems, which can affect Beijing area.

According to the frequency and intensity of sandstorms, the composition and distribution of aeolian materials, ecological conditions, soil moisture content, water and soil utilization mode and intensity, and combined with the regional environmental background, northern China is divided into four main sandstorm centers and source areas: 1, Hexi Corridor in Gansu Province and Alashan League in Inner Mongolia; 2. The area around Taklimakan Desert in southern Xinjiang; 3. The northern slope of Yinshan Mountain in Inner Mongolia and its adjacent Hunshandake sandy land; 4. Along the Great Wall in Mongolia, Shaanxi and Ningxia. The dust in the above-mentioned sandstorm-prone areas is often transported to North China and the middle and lower reaches of the Yangtze River with the westerly wind and northwest airflow, forming dusty weather.

The frequent occurrence of sandstorms is one of the signs of ecological environment deterioration. The area of desert, Gobi and desertified land in China has reached 654.38+6530 square kilometers, and it is developing at the rate of 2460 square kilometers per year. Land desertification is very different between the east and the west. Taking Helan Mountain as the boundary, the west is controlled by the arid climate in the northwest, and there is no rainfall. Land use is an oasis irrigated agricultural area. The main factors and manifestations of desertification are improper allocation of water resources, waste of downstream farmland due to lack of water or blind reclamation, firewood collection and overgrazing in the transitional zone between desert and oasis, or natural vegetation death and wind erosion in grassland due to depletion of surface water and decline of groundwater level. Affected by the East Asian monsoon, there is some precipitation in summer and autumn in the east. Desertification mainly occurs in the farming-pastoral ecotone. In the dry season of winter and spring, it is caused by excessive reclamation, serious overgrazing, grassland degradation and firewood harvesting. The main forms are soil desertification, gravel, shrub desertification and sand activation of agricultural land. At the beginning of the 20th century, the United States exploited the western land on a large scale, which led to the "black storm" that shocked the world in the 1930s. In 1960s, the land around Karakum Desert in Kazakhstan was reclaimed by the former Soviet Union, and there were also strong sandstorms. After the 1930s, the United States made great efforts to adjust the agricultural planting structure in the construction and transformation of the western region, and adopted a set of effective methods, such as crop intercropping, interplanting and crop stubble retention at different maturity and sowing dates, vigorously popularized the no-tillage method and reformed agricultural machinery. After the 1960s, the former Soviet Union attached great importance to building water conservancy projects in the construction and transformation of Central Asia, and vigorously built farmland shelterbelts, which achieved good results. It provides the world with two different technical models to prevent and control sandstorms-agricultural measures (USA) and forestry measures (former Soviet Union). We should learn from the successful experience of other sandstorm-prone areas in the world and formulate ecological restoration strategies and policies suitable for China's national conditions.

Sandstorm is the product of the interaction between weather process and ground process. However, at present, human's ability to control the weather is still very limited. The key to slow down the frequency and intensity of sandstorms lies in the ecological protection and construction of the ground. Adhere to the ecological protection and construction policy of "giving priority to prevention, giving priority to protection and paying equal attention to prevention and control"; Establish and improve the system of ecological protection laws and policies, stop all production activities that lead to the continuous deterioration of the ecological environment, and take certain ecological immigration measures for areas beyond the ecological carrying capacity.

Sandstorms may induce allergic diseases, epidemics and infectious diseases. According to him, under normal circumstances, people's nasal cavity, lungs and other organs have a certain filtering effect on dust, but sandstorms, a disastrous weather phenomenon, bring too much and too dense fine dust, which is very likely to make people with respiratory allergic diseases relapse. Even healthy people, if they inhale dust for a long time, will have uncomfortable symptoms such as cough and asthma, which will lead to the outbreak. In addition, strong winds span thousands of kilometers, blowing germs along the way to downwind areas, which may include some infectious germs.

Dust is the most harmful to human respiratory system, so people should not underestimate it. In particular, the elderly, infants and patients with respiratory allergic diseases with poor resistance should stay indoors, close doors and windows and try to stay away from dust sources. Once you find that you have obvious discomfort, you must go to the hospital immediately to find out the reason.

When you have to be outdoors, it is best to protect your eyes and mouth with wet towels and gauze towels, but it needs to be reminded that this simple protection does not work for the virus. Before the dust storm recedes, construction workers and cleaning personnel should temporarily stop outdoor work. He also suggested that people drink more water, eat more light food and don't buy street open-air food.

We hope that sandstorms will disappear one day, but in fact this idea is almost impossible to realize. We can do some analysis on the formation conditions of sandstorms. There are three conditions for the formation of sandstorms. First, wind is the original driving force of sandstorm. Secondly, there is sand source. If there is no basic material such as sand source and fine sand, there will be no sandstorm with atmospheric circulation. Thirdly, when the surface is heated (usually in the case of drought), unstable updraft will be generated, which will take the dust on the ground to high altitude, thus forming sandstorms, which are the three main reasons for the formation of sandstorms. To ask when the sandstorm will end, we must first ask whether these three factors will end.

China Academy of Forestry used the observation data of 1000 stations and 10 years distributed all over the country to simulate the conditions in arid and semi-arid areas. The results show that by 2050, the arid areas in China are still expanding, and the sources of sandstorms will still exist. In addition, it is impossible for us to control global warming and atmospheric circulation. From this point of view, natural factors seem to play a leading role in the occurrence of sandstorms. However, we should see that many human activities have intensified it. Sandstorm is a manifestation of land desertification and desertification. Although it is impossible to return to the state of "seeing cattle and sheep at the slightest sign", we are not pessimistic. Measures such as returning farmland to forests and grasslands, sand control projects, and three-north shelterbelt can be taken to reduce sand sources.

Objectively speaking, the sandstorm in China can easily affect Japan, North Korea and other countries, but they certainly suffer much less than us. One of my Japanese colleagues once said that dusty weather is not good, but it is not necessarily harmful if it really comes. We know that dust is rich in calcium, which can neutralize acid substances such as sulfur dioxide, and it is also good for Japan, a country with frequent acid rain. Even if dust doesn't have the strength to fly that far and falls into the sea halfway, it is a rare nutrient for marine life. What is the cause of sandstorm?

A: There are many reasons for the formation of sandstorms. The driving force of sandstorm is wind. The material basis is dust. Wind and dust have complex and diverse temporal and spatial changes. There is strong enough wind and enough dust. But blowing a lot of dust also requires many conditions. A strong northwest wind prevails in the arid area of northwest China. Due to the uplift of the ancient Mediterranean, a large number of soft dust deposits were formed. Drought, little rain and sparse vegetation, especially in spring, drought, strong wind and sparse vegetation all occur at the same time, so there are natural conditions for sandstorms in spring, and human activities destroy the vegetation on the ground, making sandstorms worse and worse.