Causes, hazards and prevention measures of desertification in northwest China
As the temperature warms up in spring, the ground thaws, the soil on the ground becomes loose, the ground temperature gradually rises, and the vertical air flow increases. If there is strong wind in the northern region, the dust will be blown high into the sky. A sandstorm will form~A sandstorm is a disastrous weather phenomenon in which wind and sand interact. Its formation is inseparably related to the global greenhouse effect, El Niño phenomenon, forest decline, vegetation destruction, species extinction, climate abnormalities and other factors. . Among them, over-exploitation of natural resources, excessive deforestation, and over-cultivation of land caused by population expansion are the main reasons for frequent sand and dust storms.
As a high-intensity sandstorm disaster, sandstorms do not occur in all windy places. Sandstorms are only likely to occur in areas with arid climate and sparse vegetation. In the northwest region of my country, the forest coverage rate is not high, and the poor northwest people still want to make a fortune by digging licorice, nostrils, and mining. These predatory and destructive behaviors have aggravated the sandstorm disaster in this region. Bare land can easily be blown up by strong winds to form sandstorms or even strong sandstorms.
After large-scale sandstorms occurred in late winter and spring, the dust raised by strong winds caused a large amount of dust in the air, which blocked the local sunshine and even reduced visibility to zero. Therefore, super strong sandstorms are also called black sandstorms. storm. Sandstorms can cause heavy losses to people's lives, property and agriculture. Sandstorms mainly originate in desertified areas, where the soil is soft, the ground is dry, and there is no vegetation on the surface. Once the air in a large area is very unstable and the ground wind speed is very high, it is easy to blow up the surface dust into the air and form a dust weather.
After a sandstorm occurs, most of the larger dust particles settle to the ground after affecting the source area or nearby areas, while the smaller particles can be transported upward to an altitude of 1,000 to 3,000 meters, and then through The air flow in the westerly belt is carried eastward. During the transmission process, part of the dust travels farther due to diffusion or dilution; the lower the concentration, part of it reaches the ground due to sedimentation or rainfall (snow) during the transportation process. Dust from northwest China can move eastward to Japan, South Korea, and Hawaii 10,000 kilometers away, and can affect Taiwan, Hong Kong, and even the Philippines in the south. The area of influence is quite vast.
After sandstorms are transmitted to other areas thousands of kilometers away, local visibility and suspended particles in the atmosphere increase, affecting the air quality in that area. As for the time or scope of being affected by sandstorms, it depends on the scale and duration of the sandstorm at the source, and whether the meteorological conditions in the remote area are conducive to the transmission of sandstorms. According to observation records, visibility can be affected in as little as a few hours, and as long as a week, it can even cause mud rain.
Sandy weather is divided into three categories: floating dust, blowing sand, and sandstorms:
Floating dust: a weather phenomenon in which sand or soil particles suspended in the atmosphere reduce horizontal visibility to less than 10 kilometers;
Blowing sand: The wind blows up the dust on the ground, making the air quite turbid, and the horizontal visibility is within 1-10 kilometers;
Sandstorm: The strong wind blows up the dust on the ground It is a weather phenomenon that makes 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 research, sand and dust in desert areas are the main source of suspended particles in the earth. Sand and dust in the Sahara Desert alone account for 25% of suspended particles in the global atmosphere. Northwest my country is located in the desert area of Central Asia, ranking second among the four largest desert areas in the world (in order, Central Africa, Central Asia, North America and Australia). Therefore, the impact of sand and dust in northwest China on the atmospheric environment of East Asia cannot be ignored. . The conditions for the occurrence of sandstorms are:
Surface properties: soft, dry soil, no vegetation or grass growth, and no snow.
Meteorological conditions: strong and persistent surface winds, vertically unstable meteorological conditions and no rainfall or snowfall.
The total area of major deserts in northwest China is nearly 600,000 square kilometers. The main source areas are located in northwest China, North China and Mongolia, north of 35 degrees north latitude and west of 125 degrees east longitude, including Xinjiang, Gansu, Hetao, Inner Mongolia, Mongolia and other regions. The annual rainfall in this area is less than 400mm, and the seasonal distribution is quite uneven. It is the main source of sandstorms 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 year. The number of sandstorms varies every year.
The main overseas source of sand and dust that affects most parts of North China, especially Beijing, is Mongolia. The overseas dust sources that affect the dust weather in China's northern Xinjiang are mainly located in desertification zones in Kazakhstan and Russia.
The main impact of sand and dust weather in eastern China is the Mongolian vortex system. After the Mongolian vortex is formed, it usually rolls up local dust first and gradually moves southward. During the movement, the combined updraft at the tail of the low vortex draws the dust from the dust sources along the way into the low vortex and transports it downstream. Beijing is in the downwind area, and deep low vortex systems often bring sand and dust weather to Beijing.
The moving paths that affect sand and dust weather in Beijing mainly include two: the North Road starts from the eastern and western regions of Mongolia, passes through the western Hunshandake Desert in Inner Mongolia, Huade, and Zhangjiakou to Beijing; the West Road starts from It runs from the east of Hami City in Gansu Province to the China-Mongolia border in the Alxa League of Inner Mongolia, along the Hexi Corridor and south of the Helan Mountains, passing through the Mu Us Desert and Ulan Bhe Desert, Hohhot City and Zhangjiakou, and finally reaches Beijing. Sandstorms that occur on the edge of the Taklimakan Desert in Xinjiang will form long-distance transport when encountering a powerful system passing through, which can affect the Beijing area.
Based on the frequency and intensity of sandstorms, the composition and distribution of sand and dust materials, ecological status, soil moisture content, water and soil utilization methods and intensity, and combined with the regional environmental background, four major sandstorm centers and sources in northern my country are divided Areas: 1. Gansu Hexi Corridor and Inner Mongolia Alxa League; 2. Areas around the Taklimakan Desert in southern Xinjiang; 3. Areas adjacent to the northern slope of Yinshan Mountain in Inner Mongolia and the Hunshandake Sandy Land; 4. Along the Mongolia-Shaanxi-Ningxia Great Wall. Sand and dust in the above-mentioned sandstorm-prone areas are often transported to North China and the middle and lower reaches of the Yangtze River with westerly winds and northwest airflows, forming sand and dust weather.
The frequent occurrence of sandstorms is one of the signs of ecological environment deterioration. The area of desert, Gobi and desertified land in my country has reached 1.653 million square kilometers and is developing at a rate of 2,460 square kilometers per year. There is a big difference in land desertification between the east and the west. Bounded by Helan Mountain, the west is controlled by the northwest arid climate and lacks rainfall, so the land is used as an oasis irrigated agricultural area. The main factors and manifestations of desertification are improper allocation of water resources, which are caused by the abandonment of downstream farmland due to water shortage or blind reclamation, firewood harvesting and overgrazing in the transition zone between desert and oasis, or the depletion of surface water and the decline of groundwater levels in grasslands, resulting in the loss of natural vegetation. Death, wind erosion increases. Affected by the East Asian monsoon, there is a certain amount of precipitation in summer and autumn in the east. Desertification mainly occurs in the agricultural and pastoral ecotone. In the dry season of winter and spring, it is caused by indiscriminate reclamation, severe overloading or overgrazing degradation of pastures, and woodcutting. The desertification and gravel formation of agricultural land soils Morphification, shrub desertification and sand revitalization are the main forms. The United States' large-scale development of western land in the early 20th century led to the "Black Storm" that shocked the world in the 1930s; in the 1960s, the former Soviet Union reclaimed the land around the Karakum Desert in Kazakhstan, which also caused strong sandstorms. After the 1930s, the United States vigorously adjusted the agricultural planting structure in the construction and transformation of the western region, adopted a set of effective methods such as intercropping, intercropping and crop stubble retention of crops with different maturity and different sowing periods, vigorously promoting no-till methods and reforming agricultural machinery. method; after the 1960s, the former Soviet Union paid great attention to the construction of water conservancy projects and vigorously built farmland shelterbelt networks in the construction and transformation of Central Asia, and achieved relatively good results. It provides the world with two different technical models for preventing and controlling sandstorms---agricultural measures (in the United States) and forestry measures (in the former Soviet Union). We should learn from the successful experiences of other sandstorm-prone areas in the world and formulate ecological restoration strategies and policies that suit our country's national conditions.
Sandstorms are the product of the simultaneous effects of weather processes and ground processes. However, human beings' current ability to control weather is still very limited. The key to mitigating the frequency and intensity of sandstorm disasters lies in the ecological protection and construction of the ground. Adhere to the ecological protection and construction policy of "prevention first, give priority to protection, and pay equal attention to prevention and control"; establish and improve the laws and policies for ecological protection, stop all production activities that cause the ecological environment to continue to deteriorate, and take measures to deal with areas that exceed the ecological carrying capacity. Certain ecological migration measures.
Sandstorms may induce allergic diseases, epidemics and infectious diseases. According to his explanation, under normal circumstances, the human nose, lungs and other organs have a certain filtering effect on dust, but the excessive and dense fine dust caused by severe weather phenomena such as sandstorms is very likely to cause respiratory allergic diseases. of people relapse. Even healthy people, if they inhale dust for a long time, will suffer from coughing, asthma and other uncomfortable symptoms, leading to epidemics. In addition, strong winds span thousands of kilometers and blow germs along the way to downwind areas, which may include some infectious germs.
Sand dust is the most harmful to the human respiratory system and should not be taken lightly. Especially the elderly, infants and children with poor resistance, and people with respiratory allergic diseases should stay indoors with closed doors and windows and stay away from dust sources as much as possible. Once you find any obvious discomfort, you must go to the hospital immediately. Find out the cause.
When you must be active outdoors, it is best to use a wet towel or gauze to protect your eyes and mouth. However, you need to be reminded that this simple protection does not work against viruses. Construction workers and cleaning workers should temporarily stop outdoor operations until the sandstorm recedes. He also advised people to drink more water, eat more light food and not buy open-air street food.
We hope that sandstorms will one day become extinct, but in fact such an idea is almost impossible to realize. We can do some analysis on the conditions for the formation of sandstorms. Three conditions must be met for the formation of sandstorms. First, wind is the original driving force of sandstorms. Secondly, there is the source of sand. If there are no basic materials such as sand source and very fine sand, sandstorms will not form with atmospheric circulation alone. Third, when the surface is heated (usually under drought conditions), an unstable updraft is generated, which brings the sand on the ground to high altitudes, thus forming sandstorms. These 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.
The Chinese Academy of Forestry has conducted some experiments using more than 1,000 observation stations across the country and 10 years of observation data to simulate conditions in arid and semi-arid areas. The results show that by 2050, my country’s The arid areas are still expanding, and the sources of sandstorms will still exist. In addition, we cannot control global warming and atmospheric circulation. From this perspective, natural factors seem to play a leading role in the occurrence of sandstorms. But we should see that there are many human activities that have aggravated it. Sandstorms are a manifestation of land desertification and desertification. Although it is impossible to return to the state of "the wind blows the grass and the cattle and sheep are invisible", we can We are not pessimistic. We can reduce sand sources by returning farmland to forests and grasslands, desert prevention and control projects, and the Three-North Shelter Forest.
Objectively speaking, our country's sandstorms can easily affect Japan, North Korea and other countries, but their suffering is definitely much lighter than ours. A Japanese colleague of mine once said that although sand and dust weather is not good, it is not necessarily harmful when it actually comes. We know that dust is rich in calcium, which can neutralize acidic substances such as sulfur dioxide, which is also beneficial for a country like Japan that is prone to acid rain. Even if the dust doesn't have the strength to fly that far and falls into the sea on the way, it is still a rare nutrient for marine life. What causes sandstorms?
Answer: The reasons for the formation of sandstorms are very complex and multifaceted. The driving force of sandstorms is wind. The material basis is sand and dust. Wind and dust each have complex and diverse changes in time and space. There is a strong enough wind and a sufficient amount of dust. But blowing up a lot of sand and dust also requires many conditions. In the arid area of northwest my country, strong northwest winds prevail. A large amount of soft sand and dust accumulation was formed due to the uplift of the ancient Mediterranean. Drought, low rainfall, and sparse vegetation, especially drought, strong winds, and sparse vegetation all occur simultaneously in spring. Therefore, spring has the natural conditions for sandstorms to occur. Coupled with the destruction of ground vegetation by human activities, sandstorms become more intense.