What is the cause of the snowstorm?

Snow disaster, also known as white disaster, is a natural phenomenon caused by long-term heavy snowfall. It is a frequent meteorological disaster of animal husbandry in pastoral areas of China, mainly referring to animal husbandry areas that rely on natural grassland for grazing. Due to the excessive snowfall in winter, the thick snow cover and the long duration of snow cover, the normal grazing activities of animal husbandry are affected. In addition, large-scale and high-intensity snowfall will also cause various hazards to vast areas including cities. But generally speaking, the meteorological snowstorm refers to the snowstorm that affects Inner Mongolia, Xinjiang, Qinghai and Tibet.

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 (snow flow) and snow disasters in pastoral areas.

accumulated snow

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 snow above the snow balance line is greater than the melting amount in the current year, and the snow does not melt all the year round.

② Stable snow cover (continuous snow cover): seasonal snow cover with continuous spatial distribution and snow cover time (more than 60 days);

③ Unstable snow (discontinuous snow): Although there is snow every year, the temperature is low, but the snow is discontinuous in space, mostly distributed in points, and the number of snow days in time is 10~60 days, and it 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, due to the attack of cold wave or strong cold air, large-scale snowfall occurs, 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.

Definition and index of snowstorm

Snow can play a positive role in the wintering and heat preservation of pasture, and snow melting in dry season can increase soil moisture and promote the green growth 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.

Snowstorms can be divided into two types according to their climatic laws: sudden and persistent. Sudden snowstorms will occur during or after snowstorm weather, and the thick snow lasting for several days will pose a threat to livestock. This kind of snowstorm usually occurs in late autumn and early spring with changeable climate, such as the rare snowstorm from late March to early April in Qinghai Province 1982 and the middle of l0 in 1985, which is the most obvious example of this kind of snowstorm in recent years. The thickness and density of the snow that harms livestock gradually increase with the snowfall, and it takes a long time for the snow to stabilize. This type can last from late autumn to the following spring, such as the severe snowstorm in Qinghai Province 1974 10 to March 1975, which lasted for five months, and the extreme minimum temperature dropped to MINUS 30-40 degrees.

People usually regard the depth of grassland snow as the primary sign of snow disaster. Due to the different growth heights of grassland and pasture, the depth of snow forming snowstorm is also different. According to the analysis of observation and investigation data in Inner Mongolia and Xinjiang for many years, and comparing the relationship between snowfall and blizzard formation over the years, the blizzard indicators are as follows:

Light blizzard: the snowfall in winter and spring is equivalent to more than 120% of the thunderstorm in the same period;

Moderate snowstorm: the snowfall in winter and spring is equivalent to more than 140% of the snowfall in the same period of the year;

Heavy snowstorm: the snowfall in winter and spring is equivalent to more than 160% of the snowfall in the same period of the year.

Snow disaster index can also be expressed by other physical quantities, such as snow depth, density and temperature. However, the biggest advantage of the above indicators is that they are easy to use and the data are easy to obtain.

Harm to animal husbandry

The main reason is that snow covers the grassland and exceeds a certain depth. Some snow is not deep, but the density is high, or the snow surface is covered with ice to form an ice shell, which makes it difficult for livestock to open the snow layer and eat grass, causing hunger. Sometimes the ice shell is easy to cut the ankles of sheep and horses, causing frostbite, often causing livestock to abort, and the survival rate of young animals is low, and the old, weak and young animals are hungry and cold, leading to increased deaths. At the same time, it also seriously affects or even destroys lifeline projects such as transportation, communication and power transmission lines, posing a threat to the life safety and life of herders. 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. 1992- 1993 At the turn of winter and spring, heavy snow fell successively in parts of Inner Mongolia, Qinghai, Tibet and Gansu provinces, affecting more than 300 million mu of grassland, with the affected population11million people and dead livestock1million heads.

Regularity of snow disaster in pastoral areas

According to the analysis of investigation materials, the snowstorm in grassland and pastoral areas in China has the law of once every ten years. 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 herder has a big snowstorm, it rarely happens year after year.

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. Then there was a continuous snowfall, which made the grassland snow thicker and thicker, so that the snow that harmed livestock lasted all winter.

The area where the snowstorm occurs is closely related to the distribution of precipitation. Such as pastoral areas in Inner Mongolia; Snowstorms mainly occur in Bameng, Wumeng, Ximeng, Zhao Meng and northern Zhemeng in central Inner Mongolia, with a frequency of more than 30%, with the heaviest and most frequent snowstorms in Yinshan area. Due to the unusually dry winter in the west, there are almost no snowstorms. In pastoral areas of Xinjiang, snow disasters are mainly concentrated in mountain pastures around Junggar Basin in northern Xinjiang. Snow disasters rarely occur in southern Xinjiang except in the western mountainous areas. In Qinghai pastoral areas, snowstorms are mainly concentrated in Hainan, Guoluo, Yushu, Huangnan and Haixi, which have more precipitation in winter in the south. In the pastoral areas of Tibet, snow disasters are mainly concentrated in Naqu area near Tanggula in northern Tibet and Xigaze area in southern Tibet. The former is often associated with snowstorms in southern Qinghai.

Snow disaster warning signal

Snow disaster warning signals are divided into three levels, which are represented by yellow, orange and red respectively. Yellow is the third-level defense state, with orange on it, and the last yellow indicates the first-level emergency and dangerous situation.

(1) The yellow warning signal of blizzard

Meaning:/kloc-There may be snowfall within 0/2 hours, which may affect traffic or animal husbandry.

Defense guide:

1, relevant departments should prepare for snow prevention;

2. The transportation department should prepare for road snow melting;

3, agricultural and pastoral areas to prepare food and grass.

(b) Snowstorm orange warning signal

Meaning: There may be snowfall that has a great impact on traffic or animal husbandry within 6 hours, or there has been snowfall that has a great impact on traffic or animal husbandry and may continue.

Defense guide:

1, relevant departments should do a good job in road cleaning and snow melting;

2. Drivers should drive carefully to ensure safety;

3. Drive wild livestock into the fence to feed;

Other yellow warning signals of the same snowstorm.

(3) Red snowstorm warning signal

Meaning: There may be snowfall that has a great impact on traffic or animal husbandry within 2 hours, or there has been snowfall that has a great impact on traffic or animal husbandry and may continue.

Defense guide:

1, close road traffic if necessary;

2. Relevant emergency departments should be ready to start the emergency plan at any time;

3. Do a good job in disaster relief in pastoral areas;

Other orange warning signals of the same snowstorm.