What are the hazards and causes of snowstorms?

On June 65438+1October 10, 2008, a snowstorm broke out in southern China. The severely affected areas are Hunan, Guizhou, Hubei, Jiangxi, northwestern Guangxi, northern Guangdong, western Zhejiang, southern Anhui and southern Henan. As of February, 2008, 12, 2 1 provinces (autonomous regions, municipalities and corps) in China were affected by freezing rain, snow and ice disasters to varying degrees, resulting in 107 deaths, 8 missing, and 15 12000 emergency. The affected area of crops was 65.438+0.77 billion mu, and the harvest was 2530 mu. The damaged forest area is nearly 260 million mu; 354,000 houses collapsed; Causing direct economic losses of RMB111100 million yuan.

snow disaster

What is the weather cause of this snowstorm? The main reason for the formation of large-scale rain and snow weather process is the abnormal atmospheric circulation, especially in Eurasia.

Atmospheric circulation has its own operating rules, and it keeps a stable circulation state for a certain period of time. There is a low-value system in the southwest of Qinghai-Tibet Plateau, while Siberia maintains a relatively high-value system, namely, meteorological low-pressure system and high-pressure system. These two systems have existed in these two areas for a long time, and the low-pressure system has brought abundant precipitation to the southern part of China, mainly in the southern sea and the Indian Ocean. Cold high pressure from Siberia pushes cold air to the south. In general, the cold air from Siberia is the main control factor in winter, which makes most parts of China dry and cold.

On June 5438+ 10, 2008, the warm and humid air flow in the southwest affected most parts of China, while the high-pressure system in the north was stable, and the cold air was continuously transported from Siberia to the south, so the cold and warm air met in the middle and lower reaches of the Yangtze River and the south. The density of cold air is relatively high, and warm air will slide upward along the cold air layer, so the rich water vapor carried by warm and humid airflow will condense, forming rain and snow weather. Due to the unusually long-term intersection of cold and warm air in this area, the rainy and snowy weather in southern China lasts for a long time.

In fact, the three rain and snow weather processes in the south are mainly the three strengthening of the warm and humid airflow in the southwest, and three relatively large rain and snow weather processes have appeared accordingly.

Among them, the third large-scale continuous rain and snow weather process on June 26-28, 2008 was strong, and the impact of the previous two times caused the most serious losses.

Overview of snowstorm

Snow disaster, also known as white disaster, is a natural phenomenon caused by long-term heavy snowfall. It will seriously affect or even destroy lifeline projects such as transportation, communication and transmission lines, and pose a threat to people's life safety and life. Snow disasters mainly occur in stable snow-covered areas and unstable snow-covered mountainous areas, and occasionally appear in instantaneous snow-covered areas. Snow disasters in pastoral areas in China mainly occur in Inner Mongolia grassland, northwest China and parts of Qinghai-Tibet Plateau. According to the formation conditions, distribution and manifestations of snow disasters in China, snow disasters can be divided into three types: avalanche, wind-blown snow disasters and snow disasters in pastoral areas.

Types and effects of snow cover

A snowstorm is a disaster caused by snow. According to the stability of snow, the snow in China can be divided into five types:

(1) Permanent snow: the amount of snow is greater than the melting amount of the current year, and the snow will not melt all the year round; (2) Stable snow (continuous snow): seasonal snow with continuous spatial distribution and snow accumulation time (more than 60 days); (3) Unstable snow (discontinuous snow): Although there is snow every year and the temperature is low, the snow is discontinuous in space and mostly distributed in points. The number of snow days in time is 10 ~ 60 days, which is intermittent; (4) Instantaneous snow: It mainly occurs in South China and Southwest China where the average temperature is relatively high. However, in the year when the monsoon is particularly strong, large-scale snowfall occurs due to cold wave or strong cold air, but it melts quickly, resulting in short-term (generally no more than 10 day) snow on the surface; 5. It doesn't snow: Except for some high-altitude mountainous areas, it doesn't snow all the year round. Snow disasters are mainly distributed in stable snow-covered areas and unstable snow-covered mountainous areas, and occasionally appear in instantaneous snow-covered areas.

Snow can play an active defensive role in the wintering and heat preservation of pasture, and snowmelt in dry season can increase soil moisture and promote the regrowth of pasture. Snow is also the main water source of water-deficient or waterless grassland in winter and spring, which solves the problem of drinking water for people and animals. Too much snow, too deep snow and too long duration make it difficult for livestock to eat grass, or even unable to eat grass, leading to snowstorms.

Blizzard law

During a snowstorm, winter snow usually begins at 10, and Chun Xue usually ends in April. What is more harmful is generally the so-called "sitting in winter snow" formed by heavy snow in late autumn and early winter.

Law of snow disaster in pastoral areas: According to the analysis of investigation data, snow disaster in grassland pastoral areas in China has the law of 10 once a year. As for the general snowstorm, its frequency is more frequent. According to statistics, pastoral areas in Tibet are about once every two to three years, and so are pastoral areas in Qinghai. In pastoral areas of Xinjiang, due to the great differences in climate and geography, the frequency of snowstorms varies greatly. The frequency of snow disasters in winter pasture and spring and autumn pasture in Altai Mountain, western Junggar, northern Xinjiang along Tianshan Mountain and western mountainous area of southern Xinjiang reaches 50% ~ 70%, that is, snow disasters occur in 5 ~ 7 years in 10. Other regions are below 30%. Snowstorm-prone areas are often serious, such as Altay, Fuyun and other places. The frequency of snowstorms is as high as 70%, and severe snowstorms are as high as 50%. On the contrary, areas with low frequency of snowstorms are often areas with light snowstorms. For example, the frequency of snowstorms in hot springs is only 5%, and it is a mild snowstorm. However, no matter which pastoral area, snowstorms occur in young years.