The climate forecast for this winter released by the China Meteorological Bureau on the 4th shows that the cold air activities affecting China this winter are frequent and strong, the temperature in the central and eastern regions is mainly cold, and the precipitation is generally distributed in the north and less in the south. As the "Double La Nina Year", how cold will it be this winter? Will there be a large-scale rain, snow and freezing disaster? What precautions should we take?
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Frequent cold air activity
Cold temperature does not mean cold winter.
Earlier, the National Climate Center said that a weak to moderate intensity La Nina event would be formed this winter. In the winter when most La Nina events reach their peak, the cold air activities affecting China are more frequent and stronger than normal. In view of the La Ni? a event in autumn and winter from 2020 to 2021, 2021 will be the "Double La Ni? a Year". Under the "double influence", many people are concerned about whether this winter will be cold?
The forecast shows that the cold air activities affecting China this winter are frequent and strong, and the temperature in the central and eastern regions is generally cold. Among them, Liaoning, central Inner Mongolia, Beijing, Tianjin, Hebei, Shanxi, northwestern Shaanxi, northern Henan, Shandong and northern Xinjiang will be 1℃-2℃ lower.
Jia Xiaolong, deputy director of the National Climate Center, said that the concept of cold is different from that of cold winter. Cold refers to whether the temperature is low or high on average, but there are strict criteria for judging cold winter. The basic factor of judging cold winter is the average temperature in winter for three months, which is divided into three levels in space: single station, regional and national.
Single station cold winter means that the average temperature anomaly of a single station is less than or equal to -0.43 times the standard deviation; Regional cold winter means that the number of cold winter stations exceeds 50% of the total number of regional stations; The national cold winter requires the cold winter area to exceed 50% of the national effective area. Therefore, the criteria for judging cold winter are related to the degree and range of low temperature.
"Cold winter is more a comprehensive evaluation and judgment of winter climate conditions. This year, we expect that the possibility of low temperature is relatively high, but whether it can reach cold winter depends on the standard." Jia Xiaolong said.
In addition, La Nina event is only one of the factors that affect China’s winter climate. Snow in the middle and high latitudes and changes in Arctic sea ice will increase the uncertainty of winter climate. By analyzing 15 La Ni? a events since 1951, it is found that the winter temperature in China is low in 10 La Ni? a years, high in 5 La Ni? a years, and the latest high occurred in 2020.
Although there were four cold waves in the last winter, the cold wave in early January made the minimum temperature of several meteorological observation stations break through or reach the historical extreme value since the establishment of the station. However, the news released by the National Climate Center in March this year said that the winter from December 1, 2020 to February 28, 2021 was warm. Professional judgment standards are sometimes different from the actual experience of the public. Compared with the average temperature, extreme events with abnormal temperature fluctuations are more likely to attract attention.
Image source: China Meteorological Bureau
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Intraseasonal cold and warm fluctuations
There is a high possibility of staged extreme cooling events.
The forecast shows that in December 2021, except for the low temperature in the northeast and eastern Inner Mongolia, the temperature in most parts of the country is close to normal or high. From January to February 2022, the cold air activity will obviously become stronger, and the temperature in most parts of central and eastern China may be lower than normal, so it is very likely that there will be a staged extreme cooling event. The northeast, north China, the eastern part of northwest China, northern Xinjiang and other places may have staged strong cooling and heavy snowfall.
Experts said that the volatility in this winter season is relatively large, and it is not ruled out that there will be a strong cold wave event, and the impact on the north is more obvious. Under the background of global warming, the climate system is more unstable, and the frequency and intensity of extreme events are higher.
From November 4th, the cold wave will affect most parts of China from northwest to southeast, and the cooling range is generally 8℃-10℃, and the cooling range in some areas may exceed 16℃. Along with the "cliff-like" cooling, there are strong winds, rain and snow, and the Central Meteorological Observatory continued to issue a yellow warning of cold wave on the 4 th.
At the same time, the forecast shows that staged low temperature, rain, snow and freezing weather may occur in the eastern part of Southwest China and the western part of Jiangnan. According to experts’ analysis, unlike the large-scale continuous rain, snow and freezing weather in the south in 2008, the water vapor conditions in the south this year are not as good as those in 2008, and it is unlikely that large-scale and continuous low-temperature rain, snow and freezing weather will occur, but we should pay attention to the adverse effects of phased low-temperature rain, snow and freezing weather on power grids and transportation.
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Precipitation is generally more in the north and less in the south.
Experts warn against the adverse effects of climate.
In terms of precipitation, the forecast shows that there are more places in the northern part of Northeast China, most of North China, northern Huanghuai, eastern part of Northwest China, northern part of Southwest China and northern Xinjiang than normal, including eastern Heilongjiang, southwestern Hebei, most of Shanxi, Shaanxi, Ningxia, eastern Gansu, northern Sichuan, northern Xinjiang and other places.
This year, the precipitation in many places in the north is more than normal, which is in sharp contrast with the drought in some parts of the south. According to the forecast, the precipitation in this winter will remain more in the north and less in the south. Experts said that this is mainly affected by relatively active cold air activities and strong water vapor transport to the north.
Since summer, the distribution of atmospheric circulation in the middle and high latitudes in Europe and Asia has led to the active cold air in the northwest path. At the same time, the ridge line of the western Pacific subtropical high continues to be northward compared with the normal period, and the water vapor transport from the northwest Pacific and the Indian Ocean is obviously strong. The strong and persistent warm and humid airflow in the south and the active cold air in the north frequently meet in the north, which leads to obvious precipitation in the Yellow River basin and Haihe River basin. However, the middle and lower reaches of the Yangtze River, Jiangnan and South China are under the control of subtropical high, with high temperature and little rain, and the accumulated precipitation is significantly less than that in the same period of normal years, and even moderate to severe meteorological drought occurs in some areas.
"On a longer scale, the lasting impact of La Nina is a very important reason. In addition, global warming has also led to an increase in precipitation in the northern region." Jia Xiaolong said.
Experts have warned that there are more and stronger cold air in China this winter, especially in the northern region, where there may be staged strong cooling and heavy snowfall, and in the southern region, there may be staged low-temperature rain, snow and freezing weather, which will have a greater impact on agriculture, transportation and infrastructure. Drought should be prevented in areas with less precipitation in the south, and forest fire prevention should be strengthened in areas with higher temperature and less rainfall in the southwest in winter. At the same time, the climate fluctuates greatly during the winter season, so the public should pay attention to the weather changes nearby in time and add clothes to keep warm.
Reporter: Huang Wei
Source: Xinhuanet