General characteristics of spatial distribution of freezing disasters in China

first, the meaning of freezing disaster

The freezing disaster is mainly caused by the cold air going south in the north and the sudden drop of temperature, which endangers the growth and development of crops, affects people's normal life and work, and even causes animal and plant casualties and operational accidents. Freezing disasters include cold wave, chilling injury, freezing injury, freezing rain, ice injury and snow injury.

cold wave refers to a large-scale strong cold air activity. In the process of invading south, cold air is called cold wave when it reaches a certain standard, and it is called cold air when it fails to meet the standard. China's Central Meteorological Observatory stipulates that when a cold air cools the middle and lower reaches of the Yangtze River and its northern area by more than 1℃ within 48 hours, the lowest temperature in the middle and lower reaches of the Yangtze River reaches 4℃ or below, and there are strong winds of magnitude 5 ~ 7 in three major administrative regions on land and strong winds of magnitude 7 or above in three coastal areas, it is regarded as the standard for issuing and broadcasting cold wave warnings; If the minimum temperature drops by more than 14℃ within 48 hours, there are 3 ~ 4 large administrative regions on land with a magnitude of 5 ~ 7, and there are strong winds with a magnitude of 7 or above in all coastal areas, it will be used as the standard for broadcasting strong cold wave warnings. Due to China's vast territory and great differences in climate, local meteorological stations have also formulated cold wave standards suitable for local conditions. For example, according to the meteorological department of Jiangsu Province, any cold air activity with a temperature drop of ≥ 1℃ and a minimum temperature of ≤ 5℃ within 24 hours and a gale of magnitude 5 or above is a cold wave process. The chilling injury is mainly caused by low temperature, which harms crops, fruit trees, flowers and livestock. Freezing injury is mainly caused by freezing crops and livestock, freezing and cracking water pipes and oil pipes. Freezing rain is mainly due to the low temperature. When the rain falls on wires, branches and roads, it will freeze immediately, which will increase the weight of wires and branches and break them. Freezing roads will affect traffic. Ice damage is mainly caused by the freezing of water surface and road surface, which affects traffic, and ice floes and ice dams can also cause disasters; Snow damage is mainly caused by poor visibility when it snows. Snow covers grasslands, causing livestock to die for lack of food. Snow covers roads and causes traffic accidents. Avalanches in mountainous areas can cause serious disasters. Second, the harm of freezing

When cold waves and cold air invade south, there are often strong winds, cooling, rainfall and snowfall, which cause serious harm to industrial and agricultural production and people's lives. Cold waves and strong winds often cause sandstorms in northwest China. For example, from May 4 to 6, 1993, sandstorms occurred in more than 1 million square kilometers in four or five provinces and regions in western China. The sand and dust were dark, which not only polluted the air, but also affected the traffic. This rare sandstorm killed more than 1 people and directly lost more than 5 million yuan. Cold wave and strong wind often affect fishery production at sea in coastal areas, and even cause capsizing accidents. The heavy snow brought by the cold wave will also cause a "white disaster" in the vast pastoral areas in the north. "White disaster" refers to a winter and spring snowstorm in grassland grazing. Too much snow falls in the winter half year, the snow layer is too thick, the snow layer lasts for a long time, and the snow buries the pasture, which affects the grazing or inability of livestock to eat, causing starvation or illness, and even a large number of livestock die. White disasters mainly occur in Inner Mongolia grassland, northwest China and parts of Qinghai-Tibet Plateau. For example, from October 26 to 29, 1977, a severe snowstorm occurred in the pastoral area of Xilin Gol League, Inner Mongolia, and the temperature dropped after the snow, resulting in a severe white disaster. More than 3 million livestock died, accounting for two-thirds of the total number of local livestock. For another example, from October 1999 to April 2, there were successive snowfalls in the northwest, with strong winds of 8 ~ 12, and the temperature in some places dropped to about-5℃. In some places in Inner Mongolia, the snow depth was 7 cm, and 127 towns in northern Tibet suffered from severe snowstorms. The average snowfall depth in Altay Mountain in Xinjiang was over 1.2 meters, and the deepest part in mountainous areas was 2 meters. Avalanches occurred in Yili and Yigong, and the Yigong River was blocked by mudslides. The upstream backwater exceeded the historical record, and the downstream was cut off. More than 1, people were trapped in Yigong ditch, and power supply equipment, communication and traffic were interrupted in many places. The snow depth of Bomi-Basu section of Sichuan-Tibet Highway is 1-2 meters, and local people and more than 5 tourists entering Tibet are trapped. According to preliminary statistics, there are more than 8, affected herders, 2 million affected livestock, more than 72, deaths and direct economic losses of at least 5 million yuan.

The heavy snow and snow brought by cold wave will seriously affect traffic and even cause accidents. Snow and avalanches blocked railways and highways, and snow and icy roads caused traffic accidents. For example, at the beginning of 1969, there was continuous heavy snow in the Guozigou area of Huocheng in the west of Tianshan Mountain, with the snow depth reaching 2 meters. At the same time, there was a big avalanche. More than 1, cubic meters of snow piled up on the 4.5-kilometer road from Ertai to Guozigou, and the snow pile was as high as 4 to 5 meters. Traffic was interrupted for one month, and thousands of people froze to death before and after. Another example is that on December 21, 1982, a truck in Changtu County, Liaoning Province was driving on the Shen-Chang highway with ice and snow, and the road surface was slippery. When the driver found that two bicycles were coming head-on, he braked suddenly to avoid collision, and the car turned around 18 degrees after skidding more than 3 meters because of the too fast speed, and two cyclists were killed at the rear of the car. Another example is at the end of April, 1983, heavy snow fell continuously in Qiqihar, Heilongjiang, and the snowfall in three days reached 8 ~ 9 mm (equivalent to the thickness of new snow of 8 ~ 9 cm), which led to various railway accidents one after another, resulting in water and power cuts and communication interruptions, which had a great impact on transportation.

The snow and ice weather brought by the cold wave will also cause serious disasters in Jiangnan area. For example, in late December, 1991, there was snow and ice in Shanghai, and the first 25 days of the month were particularly warm. The average temperature in the first and middle months was 3.5℃ and 2.℃ higher than that in the same period of normal years, but the temperature dropped sharply in the latter part. On the 26th to 27th, heavy snow fell in Shanghai, with a depth of 5-1cm. The snow did not melt for three days, and the road surface was severely frozen. On the 29th, the lowest temperature dropped to 8℃ below zero, which caused the city's 5. At the same time, it also seriously affected traffic. Hongqiao International Airport, Expressway and nanpu bridge were closed, tracks were buried in snow, hundreds of trains were delayed, delayed or stopped, and road traffic accidents occurred frequently, with more than 1 accidents on the 27th alone. The number of patients suffering from skating and bone injuries on icy roads soared to nearly ten times.

the low temperature brought by the cold wave will also cause great disasters to the warm south. For example, from December 17, 1999, strong cold air from the north swept across Guangdong province from north to south, and sustained low temperature and extensive frost and freezing weather generally appeared from 21 to 27, which caused severe disasters in Guangdong, with the area affected by crops alone reaching 15 million mu, among which bananas, lychees, mangoes, pineapples, vegetables, potatoes and corn were the most seriously affected crops, with a record direct economic loss of 1.85 billion yuan.

The intense cooling caused by cold wave can also induce diseases such as cold, tracheitis, coronary heart disease, stroke, asthma, myocardial infarction, angina pectoris, migraine, hypertension, etc., and it can also make patients with these diseases worse or even die. According to medical meteorological research, 77% of patients with myocardial infarction and 55% of patients with other types of coronary heart disease are particularly sensitive to the sudden drop in temperature, and the incidence of myocardial infarction has increased significantly. Statistics also show that the incidence of cardiovascular and cerebrovascular diseases has increased significantly in cold weather below ℃, and the mortality rate has also increased significantly. Therefore, some people regard ℃ as a meteorological warning of cardiovascular and cerebrovascular diseases. According to relevant statistics, the death toll of stroke and myocardial infarction is almost twice that of warm season every year in cold winter, especially in the elderly, the death rate of cor pulmonale, coronary heart disease, stroke, arteriosclerosis and hypertension is higher. In addition to the disasters caused by the cold wave in winter, cold weather in spring, summer and autumn, "cold in late spring", low temperature in summer, cold dew wind and frost will also cause cold damage.

"late spring cold" is a phenomenon that the temperature is obviously lowered due to the invasion of cold air in the process of warming up in spring, which is harmful to crops. It is the main disastrous weather during the sowing and seedling raising period of early rice in southern China, and it is an important reason for the rotten seeds and seedlings of early rice. Low temperature in summer refers to the phenomenon that the temperature from May to September is continuously lower than that in the same period of normal years, which is a large-scale disastrous weather in northeast China. Due to the continuous low temperature, the accumulated temperature required for crop growth is not enough, resulting in serious production reduction; Cold dew wind refers to a disaster phenomenon that strong cold air moves south early in autumn before and after the "cold dew" solar term, which obviously lowers the temperature in Jianghuai and the south area, affects the heading and flowering of rice in the later season and leads to a reduction in production. Frost refers to a short-term low-temperature disaster in late spring and early autumn, in which the temperature of soil surface, plant surface and near-surface air layer drops below ℃ due to the invasion of cold air, which destroys plant protoplasm and leads to plant injury and death. Frost can be divided into white frost and black frost. When the water vapor content in the air is high and the temperature drops, it reaches saturation. The water vapor directly condenses into ice crystals and condenses on the surface of plants to form a layer of white frost called white frost. If there is little water vapor in the air, it will not reach saturation when the temperature drops, and there will be no frost on the surface of plants, but the air has dropped below ℃, causing crops or flowers and other plants to suffer from freezing damage, and the branches and leaves will wither and die and turn black, so it is called black frost.