What is the cause of sandstorm?
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.
Sandstorms mostly occur in April-May every year, taking northwest China as an example. At this time of year, the Hawaiian high is formed in the Pacific Ocean, the Indian low is formed in the Asian continent, and the strong south wind blows from the ocean to the land. The Mongolian high, which controls the mainland, began to move from west to north, where cold and warm air currents met, and the heavy Siberian cold current came quickly from west to east, often forming strong winds. The wind force that forms sandstorms is generally above 8, and the wind speed is about 25 meters per second. In addition, the formation of sandstorms requires sufficient sand sources, and dust can be blown off the ground by the wind. The northwest is deep inland, and the forest coverage rate is not high. Most of the surface is desert and grassland, and there are many sandy wasteland, which provides conditions for the formation of sandstorms. Moreover, poor northwest people also want to make a fortune 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.
In the natural state, sandstorms are generally small in scale. However, due to people's excessive cultivation and overgrazing of grassland, a large area of grassland has become wasteland, increasing the frequency and intensity of sandstorms. In the 1930s, during the development of the Great Plains in the western United States, a large number of forests and grasslands were cut down, resulting in a large area of grassland turning into a desert, which triggered three famous "black storms". According to a black storm that swept across the North American continent in 1934, it was estimated afterwards that about 300 million tons of fertile soil was blown away at that time, and the amount of dust falling in Chicago reached12.42 million tons a day.
There are many hazards of sandstorm: 1, people and animals die, buildings collapse and agricultural production is reduced. Sandstorms are as harmful to people, animals and buildings as typhoons and tornadoes. 1On May 5, 1993, a serious sandstorm occurred in four provinces in northwest China, resulting in 85 deaths and 3/kloc-0 missing, with direct losses as high as 540 million yuan. 1August, 999 14 Since the early morning, moderate-intensity sandstorms have appeared in Dunhuang and other areas in Hexi Corridor, Gansu Province. The instantaneous wind speed reaches 14 meter per second, and the visibility is between 200 and 300 meters. Sand and stones are flying like dusk, (casualties are still being counted). In the past five years, the northwest of China has been hit by sandstorms for more than 20 times, resulting in economic losses of more than 654.38+0.2 billion yuan, and more than 200 people have died and disappeared.
2. Air pollution and topsoil loss. Dust storms contain at least 38 chemical elements, which greatly increase the concentration of atmospheric solid pollutants and cause long-term and potential harm to the atmospheric environment, soil and agricultural production in the producing area, surrounding areas and downwind areas. Especially after the meager topsoil on which crops depend is scraped away, the barren land will seriously affect the yield of crops.
The most important way to prevent and control sandstorms is to increase the vegetation coverage on the surface. Specifically, planting trees and grass and fixing sand. Since the founding of New China, the Three-North Shelterbelt connecting Northeast China, North China and Northwest China has planted trees and grass on the edge of the desert, which has played an important role in preventing and controlling sandstorms. According to the statistics of Yulin City, located in the north of Shaanxi Province, due to years of planting trees and grass, sandstorms have been reduced from 66 days a year in the 1950s to 5 days a year now.