Plateau , dust storms and human
- Original title: Sandstorm Why blame the Qinghai-Tibet Plateau
author? /Fan Xiao
On March 15, 2021, Beijing was hit by the most intense sandstorm in the past 10 years. But far beyond Beijing, the dust storm affected the entire Northwest, North China, and the Korean Peninsula. It also crossed the Yangtze River and affected parts of southern China.
Meteorological experts said that the dust storm was caused by a powerful cyclone in Mongolia of . The so-called cyclone is a large-scale air vortex produced by the atmosphere. The air pressure at the center of the cyclone is lower than the surroundings, and the vertical airflow of the cyclone is rising. In the northern hemisphere, the cyclone rotates counterclockwise.
If you compare it with a tornado, a tornado is also an air vortex with a low central pressure and a vertical rise in airflow, so the cyclone can be regarded as a super vortex to some extent. Large tornado.The diameter of the upper part of a tornado is generally a few kilometers, and the plane scale of a cyclone can range from a few hundred kilometers to three or four thousand kilometers.
The familiar typhoon is a tropical cyclone that occurs on the tropical ocean. Because it carries water vapor from the ocean, it will cause heavy rain and form a lot of precipitation.
The cause of this sandstorm is the extratropical cyclone from the north. Its origin is not the ocean, but the arid desert zone in the middle of the Asian continent, which is called the "broad sea". The cyclone provides a rich source of sand. Therefore, what the cyclone brings is not abundant precipitation, but a huge amount of sand and dust. The huge wind blows up and the sand flies, sweeping across the mainland and wandering.
This arid desert zone in the middle of the Asian continent is very large. It starts from Mongolian Plateau in the east and extends to the Caspian Sea in the west. Famous deserts or Gobi are: the Great Gobi in southern Mongolia (in Chinese history as the geographical boundary, the Mongolian plateau is divided into Mobei and Monan); in Inner Mongolia Dan Jaran Desert and Tengger Desert; Taklimakan Desert and Gurbantungut Desert in Xinjiang; Kizilkum Desert and Karakum Desert between the West Tianshan Mountains and the Caspian Sea. and many more.
The formation of this huge arid zone desert belt is the Late Cenozoic about 23 million years ago, especially the Quaternary which has been about 2.6 million years ago, and the strong uplift of the Tibetan Plateau result. At the beginning of the crustal uplift in the Qinghai-Tibet region, the warm and humid air currents in the Indian Ocean could still drive to the arid desert area in central Asia.At that time, it was still a scene of rivers and lakes. However, when the average altitude of in the Qinghai-Tibet region rose to more than three or four kilometers, the warm and humid air currents of the Indian Ocean could no longer climb over the highest "roof of the world" on the earth, making the vast area on the northern side of the Qinghai-Tibet Plateau increasingly arid and lakes. Shrinking and drying up, large areas of salt marshes, Gobi and deserts have gradually formed.
The uplift of the Qinghai-Tibet Plateau has not only created a huge arid desert belt on the northern side of the plateau, but also has greatly changed the terrain barriers of the Asian continent at the third pole of the earth. Atmospheric circulation situation. A westerly circulation is formed on the northwest side of the plateau, and the monsoon climate zone of East Asia is formed on the northeast-east side of the plateau. In summer and autumn, warm and humid air flows northward, and tropical cyclones-typhoons often occur; in winter and spring, dry and cold air flows southward, often producing temperate cyclones, bringing cold waves or sandstorms.
Therefore, the uplift of the Qinghai-Tibet Plateau not only created the desert belt, a huge source of sand, but also produced extratropical cyclones that drive the source of sand, thus opening the valve for sandstorms.
Some experts believe that in addition to Central Asia , the formation of deserts in the Middle East, Arabian Peninsula, and North Africa are also related to the climatic effects of the uplift of the Tibetan Plateau. A tropical desert climate is formed there, and sandstorms are often caused by cyclones. For example, in the two Gulf Wars, both sides of the war were plagued by sandstorms.
Temperate cyclones have moved dust and sand, which has accumulated over the past 2.6 million years in the Quaternary.A huge loess accumulation zone was formed between the Qinghai-Tibet Plateau and the desert belt of Central Asia. Moreover, the sand and dust brought by the northwest monsoon and the westerly circulation are blocked by Taihang Mountains and Qinling Mountains. Therefore, in China's Shaanxi, Gansu, Ningjin and Shanxi regions, the world's thickest and largest loess plateau is formed. The maximum thickness is nearly 300 meters, and the area accounts for about 6.7% of China's area. One cannot underestimate the power of nature to transport deposits. According to reports, in the sandstorm in March 2002, Beijing's total dustfall was about 30,000 tons. For the deposition rate of loess, the calculation results of different experts are different. If the data of about 0.018 cm per year since the Holocene is used, the deposition thickness can reach 1.8 meters in the past 10,000 years.
Li Jijun et al. (1999) used the dust samples from the Hexi Corridor in May 1993 to compare the two samples with the samples of Lanzhou loess. The composition and particle size are basically the same. Therefore, it is believed that the loess in the historical period is also the product of the sandstorm, and the modern sandstorm is the continuation of the sandstorm process in the historical period.
Of course, the loess of the Loess Plateau is not entirely formed by the accumulation of wind and sand. There are also gravel layers deposited by flowing water and paleosol layers formed by weathering and erosion in geological history. This shows that the climate fluctuates between cold and warm, dry and wet, and changes in the paleontological community in the loess layer also prove this climate change. Just as strong dust storms do not occur every year, their time intervals also reflect climate fluctuations on a certain scale.
Qinling -Dabie Mountain, Taihang Mountain,It is impossible to completely stop the sandstorm from going south and east. Based on the author's life experience, in the Chengdu Plain in the Sichuan Basin, there are often dusty weather in spring, and a thin layer of silt can be found on the windowsill. In addition, on the terraces of the Chengdu Plain, there is "Chengdu Clay" that is several meters thick and can be up to 20 meters thick. According to research by relevant experts, it is about 130,000 years ago to 10,000 years ago in the late Pleistocene century. In a dry and cold climate, aeolian sandy soil deposits from the north of the Qinling Mountains and the west of Longmen Mountain are similar to the loess deposits in the north. .
Sand and dust storms are natural phenomena formed in a specific geographical environment. People cannot fundamentally change them. However, the excessive expansion of human activities affects the natural environment, which will aggravate the occurrence of sandstorms locally.
For example, because of Xinjiang Tarim River the upstream of Tarim River also lost a large number of dams to divert water for a long period of time. , A large area of Populus euphratica died, and the Tarim tiger and Xinjiang bighead fish became extinct. The desert expanded rapidly.
Lake Aibi at the western end of the Junggar Basin in Xinjiang. At the end of the 1940s, the lake surface was about 1,200 square kilometers. Beginning in the 1950s, due to a large number of dams on the rivers entering the lake to divert water, the original 23 rivers entering the lake were only 7 left in the 1970s, and the amount of water entering the lake decreased by 70%. Since 1984, Lake Aibi has been shrinking at a rate of 20 square kilometers per year, and the current lake surface is less than 500 square kilometers. As rivers dry up and lakes dry up, wind and sand disasters are becoming more and more serious. Span11span Jinghe County on the south bank of Lake Aibi There were 0.4 days of floating dust every year in the 1960s,In the 1990s, it has reached 44.7 days per year.
In every river and lake in Xinjiang, almost similar stories have happened to varying degrees. In April 1998, 52 counties in Xinjiang were hit by extremely strong sandstorms, which had to do with the destruction of the natural environment, especially the natural environment of rivers and lakes.
It is impossible to eliminate sand and dust storms, but it is possible to better protect the rivers, lakes and oasis environments in the desert zone to reduce the human factors that aggravate sand and dust storms.
In addition, people cannot simply regard typhoons and sandstorms brought about by cyclones as disasters. The so-called good fortune comes with misfortune, and misfortune lies on it. The precipitation brought by the typhoon is indispensable for satisfying the water resources of islands and mainland coastal areas. In 2020, due to climate change, no typhoon landed on Taiwan Island , and there are usually three or four typhoons passing through Taiwan every year. As a result, the record of the least rainfall in Taiwan in the past 30 years has been set, which has led to a significant reduction in water storage in reservoirs, and even dried up to the bottom. Taiwan has faced a water shortage crisis since the second half of 2020.
In terms of sandstorms, it can be said that without sandstorms, there would be no Loess Plateau. Most of the sediment in the Yellow River came from the Loess Plateau in the middle reaches. It was the sediment transported by the Yellow River to the lower reaches of the Loess Plateau, which accumulated and formed the vast North China Plain, which became the foundation of the Chinese civilization.
Northern loess or sandstorm dust,In terms of particle size, the content of coarse silt with 10-50 microns is the highest, which can be greater than 60%, followed by fine silt and clay particles below 10 microns, which can be greater than 35%. As for Chengdu clay, due to the longer distance of sand and dust drifting, the proportion of particles below 10 microns is higher, but the basic composition is the same as that of northern loess.
It is known that the particles below 10 microns, that is, PM10 , include PM2.5, which are inhalable particles and are more harmful to human health. However, it should be noted that the PM10 (including PM2.5) produced by the emissions of modern polluting industries is the inhalable particles formed by the interaction of nitrogen oxides, volatile organic compounds and other compounds. Its toxicity is the PM10 of natural dust. Not available. If modern dust storms are mixed with toxic inhalable particles accumulated by artificial pollution, they will be more harmful than natural dust storms in history.
Related reading: WildTibet | The Yarlung Zangbo River was "captured" and flows to the Indian Ocean WildTibet | 190,000 years ago, the Denisovans were on the Qinghai-Tibet Plateau WildTibet the second season | Guide (with map)
