What are the hazards of black storms?

There are two main hazards of black storm, one is wind and the other is sand.

There are two hazards of strong winds: one is wind damage, and the other is scraping the ground.

Let's talk about the typhoon first. Strong winds destroy buildings, blow down or pull up tree stems, tear up farmers' plastic greenhouses and farmland plastic films, and so on. In addition, April and May in Northwest China are the time when cash crops such as melons, fruits, vegetables, beets and cotton emerge, cotyledons or true leaves grow, and fruit trees bloom. At this time, they are the least resistant to sandstorms. Light leaves are covered with dust, which weakens photosynthesis, affects respiration and reduces crop yield; In the worst case, the seedlings will die, not to mention the mature results. For example,1the black storm on May 5, 1993 caused 85,000 pistils of fruit trees to be knocked down in northwest China, and 109400 shelterbelts and timber forests were broken or uprooted. In addition, the strong wind blew down the telephone poles, causing water and electricity cuts and affecting industrial and agricultural production.

When strong wind acts on loose soil in arid areas, it will scrape off a layer of topsoil, which is called wind erosion. For example,1May 5, 1993, the average wind erosion depth of black wind was 10 cm (up to 50 cm), that is, an average of 60~70 cubic meters of fertile topsoil per mu was blown away by the wind. In fact, strong winds not only blow away the fine clay and organic matter in the soil, but also pile up the sand in the soil, which greatly reduces the fertility of the soil. In addition, the strong wind with sand will wear off a layer of buildings and crops, which is called abrasion and also a disaster.

The harm of sand is mainly sand burial. As mentioned earlier, in narrow pipelines, windward and uplifted terrain, due to the high wind speed, the wind-blown sand hazard is mainly wind erosion; However, in the low wind speed terrain such as leeward depression, the main harm of sandstorm is sand burial. Such as1where sand burial occurred in the black wind on May 5, 993, the average thickness of sand burial was 20 cm, and the thickest part reached1.2 m.

More importantly, the loss of human life. For example,1May 5, 993, 85 people were killed, 264 people were injured and 3 1 person was missing. In addition, the death loss of large livestock was 1.2 million, the crops were affected by 5.6 million mu, the total length of the lifeline canal buried by sand in arid areas was more than 2,000 kilometers, and the Lanzhou-Xinjiang railway was stopped for 3 1 hour. The total economic loss exceeded 540 million yuan.

There are four sandstorm areas in the world, which are distributed in Central Africa, North America, Central Asia and Australia. The desert area is large and the wind erosion is serious. Northwest China is a part of the sandstorm area in Central Asia, with 603,800 square kilometers of desert and wind erosion land, 569,500 square kilometers of Gobi and 60,376 square kilometers of sandy land in different degrees. In addition, there are wind erosion low hills, scattered wind erosion residual piers on the Gobi surface and a large area of wind erosion soil desert. The annual precipitation in these places is below 65438±0.50mm, the vegetation is scarce, the dust material is extremely rich, and the wind erosion is strong.

According to the analysis of meteorological data since 1952, there are three high-frequency areas of strong sandstorms in northwest China. The first one is in Hexi Corridor of Gansu and Yellow River Irrigation District of Ningxia, with Minqin of Gansu as the center. The second high frequency region is in Hotan area of Xinjiang; The third high frequency zone is in Turpan, Xinjiang. They are located at the edge of Badain Jaran Desert, Tengger Desert and Taklimakan Desert, and are rich in sand source materials.

Black sandstorm strikes

In China, strong sandstorms mainly occur from March to May. An interesting phenomenon was found in statistics. Historically, April 13~ 18 and May 8 ~ 16 seem to be the "quiet periods" of strong sandstorms, and no strong sandstorms have ever occurred. Another interesting phenomenon is that Minqin County, Gansu Province, surrounded by Badain Jaran Desert and Tengger Desert, is the place where strong sandstorms occurred at the earliest (March 6-7) and the latest (July 17). Similar to Hotan area, strong sandstorms can also occur from March to June. The scope and duration of each strong sandstorm are different, and some only appear in one county, lasting 1~2 hours; Some provinces and regions lasted for several days, even affecting several provinces and regions in China. For example, the extremely strong sandstorm weather process from April 26th to 28th 1983 not only caused black storms in Turpan basin and Hotan area in Xinjiang, Qaidam basin in Qinghai, Longdong in Gansu, Yellow River irrigation area in Ningxia, Yikezhaomeng in Inner Mongolia, Yulin in northern Shaanxi and other places, but also almost swept the whole northern China.

Looking back for more than half a century, black storms in northwest China have increased year by year, which may be related to land desert and climate drought. 1993 is a year with frequent black storms, the strongest of which was May 5-6, when eastern Xinjiang, Hexi Corridor in Gansu, Alxa League in Inner Mongolia and north-central Ningxia were all attacked by black storms. Before the black storm approaches, you can see the dust storm wall composed of upper yellow, middle red and lower black, which looks like mushroom-shaped smoke clouds after the atomic bomb explosion. At a distance of 1 km, you can hear the dull roar, which is the general trend of the drums of the three armies. When the black storm crossed the border, the wind force in Jinchang, Gansu and Zhongwei, Ningxia reached 12, and the visibility dropped to zero. This black storm caused 85 deaths, 264 injuries, 3 1 missing, 1.2 million livestock deaths and losses, 730,000 livestock injuries, 370,000 hectares of crops affected, and direct economic losses of about 725 million yuan. As for the social impacts such as ecological disasters and land degradation caused by the black storm, it is difficult to assess.

The hazards of black storm to different ground objects are also different, such as the hazards of storm machinery, sand burial and wind erosion and sand cutting. The removal of wind erosion by dust caused by strong wind not only directly affects the excessive loss of soil and nutrients in the sand source area, but also pollutes the air, which has a certain impact on solar radiation and heat balance in other regions and even the whole world. Every year, the global sandstorm can move up to 10~20 tons/km2. The analysis of aerosol optical thickness by meteorological satellite data shows that sandstorm in northwest China is an important source of atmospheric aerosol, which can spread several Qian Qian meters and cover millions of square kilometers. Long-distance transportation of yellow sand will destroy fertile farmland, but it will also increase precipitation and alleviate the harm of acid rain. Observations in Japan have confirmed that the yellow sand particles from China are the main part of Japan's ice crystal condensation nuclei, which increases the precipitation in Japan. Another example is a sandstorm in April of 1988, which made the total sediment concentration in the air in Beijing area 15.7 times higher than normal. Due to the large increase of alkaline pro-MagmaElemental, the harm of acid rain has been reduced. In addition, the increase of dust particle concentration in the stratosphere will lead to the decrease of average temperature.

At present, the formation of sandstorm and its impact on the atmospheric ecological environment have attracted the attention of the global scientific community and conducted a series of studies. The research in China shows that the development of effective black storm weather protection system includes the establishment of mesoscale weather monitoring network and forecasting and early warning system; Strengthen and improve the joint defense of black storm weather; Study and formulate the protection plan of fragile ecosystem in northwest China; Strengthen the restoration and management of degraded ecological areas and vegetation protection; It is a powerful measure to reduce the harm of black storm to strengthen the popular science propaganda and education of sandstorm disaster prevention and relief knowledge.