(1) Drought is a progressive meteorological disaster with the widest scope, the highest frequency and the longest duration in China. 1. Four drought-prone centers: North China, South China, Southwest China and Jianghuai area. 2. Drought characteristics in different regions: (1) The northeast is dry in midsummer, "a little drought in three days, a big drought in five days". Because precipitation is relatively stable, the frequency of drought is relatively small. (2) There is a serious spring drought in North China, and it is said that "spring rain is as expensive as oil". The drought frequency ranks first. (3) There is a proverb in agriculture that "there is no drought in spring, and the drought in summer is halved". In July, the rain belt moved northward and was controlled by the subtropical high belt, which was prone to drought, but typhoon and rainstorm often alleviated the disaster. (4) Drought in summer and autumn in South China. (5) Drought may occur in southwest China all year round. Generally speaking, the spring drought in China is the widest and most frequent, followed by summer drought and autumn drought. 3. Relationship between drought and flood (1) Drought and flood alternate in time: the main alternate areas of drought and flood in China are the Yellow River basin, Haihe River basin, the middle and lower reaches of the Yangtze River and the Pearl River basin. (2) Drought and flood alternate in space: that is, one area is waterlogged, and another area is drought, that is, "there is no waterlogging here, and there is no drought there". 4. Serious agricultural drought disaster in China (2) Typhoon disaster 1. China is one of the few countries in the world most seriously affected by typhoons. China is located on the west coast of the Pacific Ocean. As the typhoon in the western Pacific moves to the northwest, China is extremely vulnerable to typhoon attacks. 2. Typhoon time: mainly from midsummer to early autumn. 3. Spatial distribution characteristics of typhoon disasters: the coastal area is heavier, and the southern area is heavier. 4. Loss caused by typhoon: The loss caused by typhoon accounts for about 15%-20% of the national natural disaster loss, among which the typhoon disaster in coastal provinces is the most serious. (3) Cold wave disaster 1. Occurrence time: from September to May of the following year, there are two cold wave peaks in spring and autumn, which are March-April and 10 ~ 1 1 respectively. The former is stronger. The cold wave that broke out in spring and autumn is the most harmful to crops. 2. Source: Northern Mainland and Ice and Snow Ocean. 3. Path: westward path-moving to the Sea of Japan and the northern part of the East China Sea via Xinjiang and Mongolia Plateau; The path to the north-moving to the south of China via the Mongolian Plateau; Northeast route-invading the eastern coast of China through the Sea of Japan or northeast China. 4. The influence of mountain ranges on the cold wave in China. In the east-west mountainous areas, such as Tianshan Mountain, Yinshan Mountain, Qinling Mountain and Nanling Mountain, cold air accumulates on the north side of the mountain and the disaster situation intensifies; Shannan is relatively warm and the disaster situation is weakened. The north-south mountain range forms a channel for cold air, which can be diverted south, affecting the middle and lower reaches of the Yangtze River, Guangdong, Guangxi and even Hainan Island. The altitude of Qinghai-Tibet Plateau in China is higher than the upper limit of the cold wave weather system, so it is rarely affected by the cold wave. 5. Affected areas: Except the Qinghai-Tibet Plateau and the southern valley of Yunnan, most parts of the country are affected by the cold wave. The frequency of occurrence is high, the highest in Northeast China, followed by North China, followed by Northwest China and Yangtze River Basin, and the least in South China. 6. Disasters in various places: the main manifestations in the north are gale, cooling, frost, snowstorm, etc. South China is mainly characterized by cooling, freezing injury, rain and snow. (4) sandstorm-a meteorological disaster with great influence in North China in spring (1) Concept: sandstorm is a general term for sandstorm and sandstorm; It refers to a weather phenomenon that strong winds throw a lot of dust on the ground into the air, which makes the air particularly turbid and the horizontal visibility is lower than 1 km. (2) Occurrence and prevention ① Time of sandstorm occurrence: winter and spring ② There are three basic conditions for sandstorm occurrence. One is strong wind, which is the dynamic condition for the formation of sandstorms; The second is the dust material on the ground-the material conditions for the formation of dust storms; The third is the unstable air state and the thermal conditions in some areas. ③ The most effective human action to prevent and control sandstorms is to plant trees and grass and increase the vegetation coverage, which can reduce the wind speed, reduce the dynamic conditions of sandstorms, increase humidity and adjust and change the thermal conditions in local areas; It can alleviate desertification and reduce the material source conditions of sandstorms. 5) Meteorological disaster prone area-North China 1. The most common meteorological disasters: drought, cold wave, sandstorm, hail, dry hot wind, frost, etc. Among them, drought-sandstorm and drought-insect disaster are the main meteorological disasters. 2. Reasons for frequent meteorological disasters: Many factors * * * work together to form biological disasters (1), crop diseases and insect pests 1 in China. Features: There are many kinds of disasters, and the disasters in the east are more serious than those in the west. 2. Harm: not only the crop production is reduced in a large area, but even the crop is not harvested; It also leads to large-scale deterioration of agricultural products, causing serious economic losses. 3. Several pests and diseases that are most harmful to crops and their distribution: (1) Wheat rust (including stripe rust, leaf rust and stem rust)-the most extensive and serious wheat disease in China, which occurs in all wheat areas. (2) Distribution and disaster of rice diseases (3) Distribution and disaster of cotton bollworm (2) Forest diseases and insect pests 1. Harm: the decrease of tree growth and forest death not only cause great losses to China's forestry, but also cause serious damage to forest ecological function. 2. Man-made causes of frequent forest diseases and insect pests: a large number of single plantations have replaced the original forests with rich species diversity, which has reduced the self-control ability of forests to pests. 3. Regional differences of occurrence frequency of Dendrolimus punctatus, the main pest: the frequent area is below 400 meters above sea level, the average temperature is above 25℃, and the occasional area is 400 ~ 500 meters above sea level, and the temperature is 10 ~ 25℃. (3) Locusts and rodents-the two most extensive biological disasters 1. Locust disaster: () Among them, the locust, commonly known as "grasshopper", has the most serious damage and the highest disaster rate. The damage to agriculture, forestry and animal husbandry is devastating. (2) Main species and distribution (3) Relationship between locust plague and drought and flood: drought and locust plague often occur in a chain. In dry and rainy years, the water level of rivers and lakes is reduced, and the backwater area is especially suitable for female locusts to lay eggs, which makes the number of locusts surge. If drought and lack of rain in the early stage are conducive to female locust laying eggs, and rain in the later stage is conducive to the growth of locust larvae, locust disasters will break out. 2. Harm of Rats (1): Rats not only spoil food, destroy grasslands and harm trees, but also spread diseases and endanger human health. In China, rodents have a wide area, many kinds and great harm, which has caused quite serious losses to agriculture, forestry and animal husbandry. (2) The regional differences of rodent infestation in China are significant. Agriculture in this area is characterized by common rodents. Rodent-infested areas in East Asia include most areas in Northeast China, North China and Southwest China, and all areas in East China and South China. This area has superior natural conditions and a long history of agricultural development. It is the main agricultural area in China. The damage areas of drought-tolerant rodents such as Rattus norvegicus and Mus musculus in Central Asia include most of the northwest, most of the Qinghai-Tibet Plateau and the marginal areas of Northeast China and North China. There is little precipitation in this area and the climate is dry. (4) The invasion of Mus musculus and Citellus dauricus.