Natural disaster knowledge
Natural variation on the earth, including natural variation induced by human activities, occurs at all times and everywhere. When such variation brings harm to human society, it constitutes a natural disaster. Because it brings varying degrees of damage to human production and life, including the relationship between humans and nature through labor as the medium, and the related relationships between humans. Disasters have negative or destructive effects. Therefore, natural disasters are a manifestation of the contradiction between man and nature. They have both natural and social attributes. They are one of the most severe challenges that mankind has faced in the past, present and future.
Major sudden natural disasters around the world include: droughts, floods, typhoons, storm surges, freeze damage, hailstorms, tsunamis, earthquakes, volcanoes, landslides, mudslides, forest fires, agricultural and forestry pests and diseases, etc.
Flood is a flood caused by excessive rainfall or excessive intensity (heavy rain or heavy rain), causing rivers to burst their banks, flash floods, submerged fields, destroyed buildings, and caused casualties. Floods occur frequently and intensely in our country, especially in the middle and lower reaches of the Yangtze River, the Yellow-Huaihai Sea, the lower reaches of the Liaohe River and South China. April to September every year is the flood control period for major rivers, and the country has to spend a lot of money on flood control measures. In the past 30 years, the most serious flood disaster in my country occurred in the Zhumadian area of Henan Province from August 5 to 7, 1975. The maximum rainfall in three days reached 1,605 mm (the average annual precipitation in the area is 800 mm). The heavy rain caused flash floods. The outbreak caused the earthen dams of two reservoirs to overflow and burst, flooding 1.13 million hectares of farmland, destroying 100 kilometers of the Beijing-Guangzhou railway line, killing tens of thousands of people, and causing direct economic losses of more than 10 billion yuan. In the summer of 1991, large-scale floods in the Jianghuai region became a major disaster of concern at home and abroad, with direct economic losses exceeding 50 billion yuan.
Drought is a long period of sunshine. Meteorological disasters such as high temperature and continuous little or no rain. In the early stages of its appearance, people could not feel its arrival, but as time went on, the area affected by drought expanded and its severity increased day by day. In our country, droughts occur throughout the year. In most areas, spring droughts occur frequently, are severe, and last for a long time. The occurrence of droughts is not only relatively concentrated in time series, for example, among the 170 droughts that occurred in Beijing between 1470 and 1949, 115 occurred in consecutive years; it also occurs in clusters in space, such as in the spring of 1950, most of Inner Mongolia, Gansu Droughts occurred in the Hexi Corridor, northern Hebei, and northern Shaanxi. From July to September, droughts occurred in vast areas of the Yangtze River, Huaihe River, Yellow River, and Hanshui River basins. There were 11 droughts from 1950 to 1980.
Tropical cyclone is a low-pressure atmospheric vortex originating from the tropical ocean surface. It is divided into four levels according to the wind strength near its center: level 6 to 7 is a tropical depression, level 8 to 9 is a tropical storm, level 10 to 11 is a severe tropical storm, and level 12 and above is a typhoon. There are 30 typhoons generated in the tropical western Pacific every year (accounting for 38% of the world). July to August is the peak period of typhoon activity. After forming in the tropical ocean, they move northwest. There are an average of 7 typhoons in my country every year. Coastal landing. Typhoons bring violent winds, heavy rains (80% of the highest rainfall records in my country's 15 offshore provinces are caused by typhoons), huge waves and tidal disasters, seriously threatening the safety of people's lives and property.
The previously mentioned severe floods in Henan in August 1975 were caused by the heavy rain caused by the landfall of Typhoon No. 7503, which slowed down and stagnated its movement deep into the interior and maintained low pressure. Typhoons made landfall in Taiwan and Zhejiang successively. Heavy rains occurred in 10 provinces including Fujian, Guangdong, Hunan, Jiangxi, Hebei and Henan. Among them, Henan is the most serious. The area of heavy rain accounts for one-third of the province. The maximum rainfall is 189.5 mm per hour and 1061.8 mm per hour, causing floods that are rare in a century.
The so-called tidal disaster refers to the offshore storm surge and huge waves caused by strong storms superimposed on the astronomical high tide of spring floods. The sea tide exceeds the local warning water level, destroys defense facilities, leads to flooding, and forms tidal disasters. . Tidal disasters in my country are mainly caused by typhoons and cold waves. The southeastern coast is hit hard by typhoons and is an area prone to tidal disasters. In the Bohai Sea and the northern part of the Yellow River, cold waves and cold fronts pass through in winter and spring, causing northeasterly winds above level 7 in the Bohai Sea and causing tidal disasters on the southern coast of the Bohai Sea.
Low temperature chilling damage is a sharp cooling caused by strong cold waves during the growth and development of crops. These include low temperatures in summer in Northeast my country, freezing rain in winter in the South, and low temperature damage before and after the cold dew season. Late rice in the middle and lower reaches of the Yangtze River and South China in autumn is heading and blooming. Such weather causes empty husks and shriveled rice grains, resulting in reduced yields. From January 26, 1969, a 30-degree cold wave arrived in the Yangtze River Basin, lowering the temperature by 14 to 20 degrees Celsius. Winter wheat, rapeseed, and fruit trees suffered severe freezing damage. A strong cold wave occurred from October 25 to 29, 1977, causing snow to reach a depth of 0.5 meters in Inner Mongolia and Xinjiang. Pastures were buried and livestock died in large numbers.
Earthquakes are caused by modern activities in the crust caused by the internal dynamics of the earth, and are generally divided into tectonic earthquakes (95%), volcanic earthquakes and collapse earthquakes. The reason why my country has become the region with the most severe earthquakes in the world is related to the fact that my country is located at the intersection of the Pacific Rim tectonic belt and the Mediterranean Himalayan tectonic belt, and the modern crustal activities are intense. Except for Zhejiang and Guizhou, all provinces have experienced earthquakes of magnitude 6 or above.
On January 23, 1556, an earthquake of magnitude 8 occurred in Huaxian County, Shaanxi Province. “It was an earthquake in Shanxi, Shaanxi, and Henan at the same time. The sound was like thunder, and chickens and dogs barked... or springs burst out, or houses in city corridors sank into the ground, or flat ground protruded. Shanfu... crushed the officials to death, and the soldiers and civilians reported that 820,000 people were named..." ("Records of Jiajing") It was one of the largest earthquakes in the history of our country. On July 28, 1976, the 7.8 earthquake struck Tangshan. The industrial town with a population of millions was instantly reduced to ruins. It was the first of the 10 most destructive earthquakes in the world this century.
Earthquakes are inevitable, and earthquake prediction is still a global problem. Our country has made great progress in the field of medium and long-term prediction, but only a few can make accurate predictions. Hard efforts are still needed to predict this highly difficult impending earthquake.
Landslide is a large amount of rock and soil on a slope that slides down along a certain sliding surface under the action of gravity, causing damage or burying of farmland and buildings on and below the slope, as well as the burying of people. casualties. Due to differences in natural conditions and different effects of human factors, landslide types are diverse. Our country is a mountainous and earthquake-prone country. Landslides caused by heavy rains and earthquakes have occurred frequently in history. With the development of construction, reservoirs have continued to appear. Landslides in mines, road cuttings, mountain towns, etc. During the Diexi earthquake in Maowen County, Sichuan on August 25, 1933, mountains collapsed and slid within 30 miles around. Two giant high-speed landslides, Diexi City and Longchi Mountain, came down opposite each other, blocking the Guojiang River and forming a weir with a height of more than 160 meters; 45 The water congested by the Queen of Heaven overflowed and burst, causing serious damage to hundreds of kilometers along the river. At the Yanchihe Phosphate Mine in Yuan'an County, Hubei Province, due to underground mining, the mountain cracked, and the displacement increased sharply after the rain. In the early morning of June 3, 1980, more than 1 million cubic meters of the mountain suddenly collapsed, and the buildings at the pit entrance were destroyed. Office buildings, Dormitories, a large number of mining machinery and more than 280 employees were instantly buried under more than 20 meters of gravel.
Muds flow often breaks out suddenly during the rainy season. The valley thunders and a powerful torrent carrying mud, sand and stones sweeps down, sweeping away everything in its path. Debris flow disasters have affected 23 provinces, municipalities, and autonomous regions in my country, affecting industry and mining, transportation (railways, highways, waterways), farmland, villages, water conservancy, and various facilities in mountainous towns and cities. According to information from the railway department, there are 1,386 debris flow ditches on my country's mountainous railways, threatening the safe operation of more than 3,000 kilometers of lines.
Forest fire is a fire phenomenon caused by nature or careless personnel. Extremely large forest fires are often caused by drought. Caused by special meteorological conditions such as high temperature, strong winds or lightning strikes, fires often get out of control due to underestimation. Once a fire occurs, it is beyond human power to contain it in time. my country's forest fire loss rate is continuously decreasing with the advancement of science and technology and the strengthening of forest fire management. But for my country, where the forest land coverage rate is only 13% and the per capita forest stock volume is less than 10 cubic meters, reducing losses is equally important as increasing the coverage rate. Because forest fires not only cause economic losses and casualties, but also cause serious damage to ecology and natural landscapes. 1987 Daxinganling forest fire. There are 1.14 million hectares of burned forest land, accounting for 1% of the country's forest land.
Agricultural and forestry pests, insects, weeds, and rodent damage refers to diseases and insect damage to crops and forests. Vicious weeds and rodent infestations. As far as crops are concerned, diseases, insects, weeds and rats will take away 50 kilograms of grain and other food from everyone in the country every year. There are more than 1,200 species of crop diseases and insect pests in my country, as well as rampant rodents and malignant weeds. If a large outbreak of pests and diseases becomes a disaster, it will have a major impact on my country's basic industry, agriculture.