From late July to early August (also known as "seven down eight") each year is the rainy season in northern my country and other northern regions such as North China and Northeast China, and is also a key period for flood prevention. Why does rainfall increase in the north during the "Seven Down and Eight Up" period? What will be the weather situation in the northern region in the future?
htmlOn July 18, The Paper interviewed Wang Yongguang, chief climate expert of the National Climate Center, and Zhang Bo, senior engineer of the of the National Meteorological Center, on these issues.
From the night of July 18 to the morning of the 19th, Mudanjiang City, Heilongjiang Province was hit by heavy rain. The meteorological department issued a timely warning and made every effort to provide forecast services. As of 8:00 on the 19th, Mudanjiang City had rainfall of 65.5 mm, Hailin City had 81.8 mm, 122.6 mm, and 93.7 mm in Shitougou. The picture shows the heavy rainstorm overnight causing water accumulation in many sections of Mudanjiang City. Zhang Yucheng Photo by
"Seven down and eight up" North China and Northeast China will usher in the rainy season
Pengpai News: What does "Seven down and eight up" mean? Is it aimed at a concept of time and place?
Wang Yongguang: "Seven down eight up" refers to a time period, which is literally understood as late July to early August. It is the most concentrated period of precipitation in northern China and Northeast my country, and it is also the most critical flood prevention. period. Now, according to the definition of the rainy season, it can be extended from mid-July to late August. In about one month, North China and Northeast China will usher in the rainy season and cause some catastrophic weather and climate events.
The Paper: What is the reason for the rainyness in the northern region during this period? As a key time period during the flood season, what are its characteristics?
Zhang Bo: is accompanied by the seasonal northward rise of the subtropical high pressure in the northwest Pacific. Usually from mid-June to early July, the main rain belt in my country is lifted from north to south China to the middle and lower reaches of the Yangtze River, and the area enters the plum rain period; entering mid-July In the late month, the rain belt changed again. As the subtropical high pressure once again rises northward, the southwest monsoon that affects my country will gradually advance northward. The warm and humid air flow in the southwest will advance from the south to the north China-Huanghuai region, and the coldness of the mid-latitude The air meets, so the rainy season begins in the north from mid-to-late July to mid-August.
The characteristics of precipitation in North China during this period are "high intensity, short duration, strong locality, large interannual changes, and concentrated precipitation periods." For example, the "July 21st Extreme Torrential Rain" in Beijing-Tianjin-Hebei region in 2012 was characterized by "large and rapid precipitation", but such heavy rainstorms do not occur every year. In addition, the rainfall during this stage is also affected by the terrain. For example, the precipitation in the Changbai Mountain area of Jilin is stronger due to the slope climbing terrain than that in the plain area.
Wang Yongguang: This period of time is characterized by the northern region entering a rainy season. With the rise of subtropical high pressure northward, the plum rain in the Yangtze River Basin tends to end and enters a high-temperature drought period. In addition, July and August are the active period of typhoon , and heavy rainfall is prone to occur in the eastern and southern coastal areas of my country due to typhoons.
"Seven down and eight up" rainy period is closely related to the location of subtropical high pressure in the northwest Pacific.
In late July this year, the rainfall in North China to the central and eastern Northeast China was slightly higher
Pengpai News: Compared with previous years, what is the weather and climate situation in the northern region this year? Is there any change in rainfall?
Zhang Bo: After July 21, the subtropical high pressure will show obvious westward and northward extension. At the same time, the southerly wind outside the subtropical high meets the cold air at the mid-latitude, bringing process precipitation. The rain belt is located in North China to the middle of Northeast China and Northeast China. In the eastern region, convection of precipitation is enhanced. From the current perspective, the cumulative rainfall in North China to central and eastern Northeast China in late July is slightly higher than the same period last year, and is mainly processed precipitation.
Wang Yongguang: It is expected that during this year's "seven down eight" period, the rainy areas in the north will be located in most of the Northeast, eastern North China and northern Huanghuai. Among them, the precipitation in the eastern part of Northeast China is 20% to 50%, floods may occur in the Songhua River basin, and the precipitation in the Haihe River basin is also showing a tendency to be more frequent. However, the precipitation in western North China is relatively low and meteorological drought may occur. The temperature in North China and Northwest China is 1 to 2℃ higher. During the rainfall period, phased high-temperature heat waves may occur in southern North China and eastern Northwest China.
Precipitation percentage forecast chart from July 16 to August 15, 2017.
23, there will be no large-scale high temperature weather in North China
Pengpai News: What are the characteristics of the overall situation in the northern region since the beginning of the flood season? At present, the high temperatures in the northern region continue. Will the arrival of "seven down and eight up" end the continuous high temperature situation?
Zhang Bo: After the flood season begins, the precipitation from North my country to the northeastern region in June was relatively low, and the meteorological drought in the western and southern Northeastern regions, central and eastern Inner Mongolia, and northern North China was relatively severe. After July, with the increase of precipitation, the drought has significantly alleviated. However, due to the low precipitation in the early stage, drought in Liaoning, eastern Inner Mongolia and other places is still maintained, and with the arrival of the rainy season in the north, the drought will further ease. In terms of precipitation characteristics, after June this year, the Beijing-Tianjin-Hebei region has experienced two large-scale heavy rainfall weather, both mainly process precipitation, with heavy cumulative rainfall and accompanied by strong convective weather of .
From the high temperature, from the 22nd to the 23rd, southern North China will maintain high temperatures for 2-3 days. After the 23rd, there will be no large-scale high temperatures in North China. Controlled by subtropical high pressure, until the end of July, the northern high temperature range will be mainly concentrated in the Huanghuai region. The cold vortex activity in the later stages of the Northeast region is more obvious, so there will be no large-scale continuous high temperature weather.
Wang Yongguang: In years with weak summer monsoons, summer drought is prone to occur in North China, such as midsummer in 2014 and 2015. After June this year, there were two heavy rainfall processes in North China, and Beijing's precipitation was more than that in surrounding areas. As of July 15, the water storage capacity of Miyun Reservoir has exceeded 1.8 billion cubic meters, reaching the largest since 2000, which has played a good role in replenishing water resources in the northern region and alleviating drought.
Short-term heavy rainfall may cause urban flooding
Pengpai News: What impact will "seven down eight up" have on flood prevention?
Wang Yongguang: The beginning of the northern rainy season will bring pressure on flood prevention in North China and Northeast China. This year, there will be a lot of precipitation in the Songhua River, Haihe and other basins, which may cause the river water level to rise, so we must be prepared to prevent flood conditions. In big cities, short-term heavy rainfall may cause urban flooding, causing water accumulation in low-lying areas of roads and affecting transportation. In addition, summer is a period of frequent strong convective weather such as thunder and hail, which will have a delay impact on aviation.
As the "seven down eight up" approaches, typhoons are gradually becoming active. It is expected that the intensity of the typhoons landed this year will be relatively strong, which will focus on affecting the coastal areas of southeast my country and south China. Strong typhoons may bring heavy rains, floods, strong winds and storm surge disasters, serious Threat the safety of life and property of people in coastal areas, so doing a good job in typhoon defense should not be underestimated.
The Paper: faces "seven downs and eight ups", how should the public avoid risks and defend themselves?
Zhang Bo: During the "seven down eight" period, it is necessary to prevent disasters and impacts from heavy rain and strong convective weather. Friends in northern regions should listen to and watch the weather forecast in time and pay attention to the release of relevant disaster warning signals.
When heavy rain occurs, the dangerous outdoor power must be cut off in time; do not wade rashly when going out, pay attention to safety; pay attention to prevent floods, mountain torrents, mudslides, landslides, collapses and other secondary disasters such as heavy rainfall in mountainous areas, and do not go to mountainous areas. Activities in dangerous areas, rivers, and geological disaster hazard areas.
When thunderstorms and strong winds occur, open-air activities and high-altitude outdoor dangerous operations should be stopped. People in dangerous areas and residents in dangerous houses should try to transfer to wind sheltering places. Close the doors and windows to strengthen the buildings that are easily blown by the wind and cover the buildings; try to ride a bicycle as little as possible when going out, and do not stay under billboards, temporary buildings, etc. when the wind blows.
When hail occurs, outdoor pedestrians will go to a safe place to hide as soon as possible and properly protect outdoor items and equipment such as cars and equipment that are vulnerable to hail.
In addition, summer is also a period of high lightning. At this time, try to stay indoors and not go out, and close doors and windows; outdoor personnel should hide in buildings or cars with lightning protection facilities; do not under trees, under electric poles, or under tower cranes Take shelter from the rain and do not hold umbrellas in open places.Never contact antennas, water pipes, barbed wire mesh, metal doors and windows, building exterior walls, and stay away from live equipment such as wires and other similar metal devices.
The Paper: What impact does "seven down eight up" have on agriculture? How to take good response measures?
Zhang Bo: "Seven down eight up" has two main impacts on agriculture. First, the impact of high temperature drought. Continuous high temperatures will cause obvious surface transpiration, resulting in faster soil moisture loss, which is very unfavorable for the growth of paddy fields or dry land crops. It can lead to high temperature and heat damage in rice, affecting the increase in grain weight, and is not conducive to summer corn flowering and silk sprouting. . Therefore, agricultural areas in the north and south should pay close attention to changes in soil moisture and take measures such as irrigation and protection in a timely manner to prevent high temperature from burning seedlings.
The second is the impact of heavy rainstorms and floods. Farmland areas are prone to accumulation of water after rain, so farmland in low-lying areas in the north should pay attention to clearing ditches and decreasing after rain to reduce the adverse effects of waterlogging on dryland crops such as corn and cotton.
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