The comprehensive intensity is less than the same period in 1998; Meiyu is an important inducement of this round of heavy precipitation; be wary of the flood conditions in the north of the country

Meteorologists explain the recent southern heavy rain

  The rain in the south is still falling!

  The latest news from the China Meteorological Administration on July 13th showed that on that day, there were moderate to heavy rain in many places in southern my country, and heavy rain in some areas; and in the next three days, there will be heavy rain in some parts of the southwest, even heavy rain.

  For more than a month, southern my country has suffered heavy rains successively, and rainfall in many places has set new historical records. The Central Meteorological Observatory has issued rainstorm warnings for 40 consecutive days, making it the longest time since the rainstorm warning business was launched in 2007.

  How "violent" is the heavy rain in the south this year? Why does it last so long? How long will it take to rain down in the south? What challenges will the upcoming "seventh and eighth" north main flood season bring? A reporter from China Youth Daily and China Youth Daily interviewed relevant experts from China Meteorological Administration.

Although the recent torrential rain is fierce, the comprehensive intensity is still not as good as the same period in 1998

  According to statistics from the National Climate Center of the China Meteorological Administration, since the flood season, there have been 15 large-scale heavy rainfall processes in southern my country. During the southern heavy rains from June 27 to July 9, the area covered by accumulated rainfall of more than 100 millimeters reached 2.887 million square kilometers.

  "The impact range is wide, the duration is long, the extremeness is strong, and the overlap of local heavy rainfall is high. This is a feature of the southern rainstorm since June." said Zhai Jianqing, associate researcher at the Meteorological Disaster Risk Management Office of the National Climate Center.

  The satellite monitoring report on July 12 showed that due to heavy rains and other factors, the main body of Poyang Lake, the largest freshwater lake in China, and the surrounding water area were from July 2 to July 8, and it became "large" 352 square kilometers in 7 days, reaching 4206. The square kilometer is the largest in the past 10 years. At 0:00 that day, in the water level well at the Poyang Lake Xingzi Station, the lake water ran over 22.52 meters-this is the 1998 flood level, marking the historical extreme value of Poyang Lake since it broke through the hydrological record.

  However, according to the current monitoring data of the China Meteorological Administration, although the heavy rain in the south is violent, on the whole, it still can not be compared with the 1998 heavy rain event.

  Zhai Jianqing believes that considering the scope, duration and rainfall of the rainstorm, from June 27 to July 9, the comprehensive intensity of the southern China's heavy rain ranked fifth since meteorological records, while the intensity of the 1998 heavy rain event ranked The first one.

  According to the statistics of the China Meteorological Administration, from a regional perspective, the 1998 rainstorm process covered most of the area south of the Yangtze River, and more than 250 mm of the area was concentrated in northern Jiangnan and eastern Guangxi. Whereas the 2020 heavy rain process was located on the north, concentrated in the Jianghuai, In eastern Jianghan, most of Jiangnan, Chongqing, Guizhou and other places, more than 250 millimeters are concentrated in northwestern Hunan, southeastern Hubei, northwestern Jiangxi, southwest Anhui, and western Fujian.

The rain is not stopping, what the hell is going on?

  Why are there heavy rains in the south recently? Wang Yongguang, chief forecaster of the National Climate Center, believes that the most direct influencing factor is meteorological conditions.

  In his view, the Western Pacific Subtropical High (Subtropical High) has continued to be strong since June this year, which is an important reason for the heavy rain in the south. The west side of the subtropical high leads the water vapor transport from the South China Sea and the Western Pacific to be significantly stronger, providing sufficient water vapor conditions for continuous precipitation in the southern region.

  After mid-June, the subtropical high rises to the north, the southwest wind prevails from the north of the southern Jiangnan to the Huanghuai area, and the water vapor transport is strong; at the same time, the cold air in the north frequently goes south, which makes the heating and cooling mass converge from the north of the south of the country to the Huanghuai area, forming a sustainability Heavy precipitation, obviously more precipitation.

  Wang Yongguang said that since mid to late June, the rain belt has stayed in the east of the southwest region to the middle and lower reaches of the Yangtze River, mainly because the weather system related to "Meiyu" is relatively stable.

  "Mei Yu!" In Wang Yongguang's view, it was a "monster" that triggered the heavy precipitation process.

  "The early entry into Meihe and the strong Meiyu front are the reasons for the unusually high rainfall during the Mei flood season in the middle and lower reaches of the Yangtze River." Wang Yongguang said that this year's Meiyu in the Jiangnan area was 7 days earlier than in previous years, and Meiyu's "main battlefield" - The middle and lower reaches of the Yangtze River already entered Meimei on June 9. It turned out that the South China Sea summer storm occurred earlier this year, and the location of the ridge line of the Western Pacific Subtropical High in the first half of mid-June, the two together led to the early arrival of plums in the middle and lower Yangtze River.

  Another more macro factor is global climate change.

  Huang Lei, director of the Climate Change Adaptation Office of the National Climate Center, said that at present, there is no research showing that the record high temperature of the Arctic is directly related to the heavy rain in southern China, and it is difficult to attribute a single weather and climate event, such as the recent southern heavy rain, directly to global warming.

  "But in the context of global warming, some extreme weather and climate events are indeed increasing and showing long-term trends." Huang Lei said.

  He gave a set of data: In the context of global warming, since 1951, China’s average temperature and extreme temperature have shown a significant increase trend, and some extreme weather and climate events have shown stronger intensity, more frequent occurrence, and duration Longer features.

  Huang Lei said that if anthropogenic greenhouse gas emissions are not controlled, the frequency, intensity and duration of some extreme events in the world will increase significantly according to the prediction results of climate models. One of the important performances is that extreme strong The frequency of precipitation events will also increase in most parts of the world.

Shortly "raise north" then "fall south", the pressure is reduced or a greater challenge?

  Since July, my country's main rain belt has maintained from the east of the southwest to the middle and lower reaches of the Yangtze River. From July 11 to 12, the main rain belt lifted northward in stages.

  This is just a brief rain belt "lifting north".

  According to the forecast of the Central Meteorological Observatory, from July 13 to 16, the main rain belt will "fall south" to the middle and lower reaches of the Yangtze River. During this period, the main areas of heavy rainfall will appear in the middle and lower reaches of the Yangtze River, and some areas will have heavy rains and local heavy rains.

  "It is worth noting that this coincides with the heavy rainfall from July 4 to July 7. It needs to pay attention to the superimposed impact of precipitation." Ma Xueqian, chief forecaster of the Central Meteorological Observatory said.

  According to Ma Xuejian, even if the eastern part of the rain belt rises north in mid-to-late July, the pressure for flood control in the Yangtze River Basin will not be reduced. The obvious precipitation in the middle and upper reaches of the Yangtze River will still pose a threat to rivers and lakes with high water levels.

  Experts reminded that the follow-up on "seven times and eight times" is more worthy of vigilance.

  According to the forecast of the China Meteorological Administration, in late July, the rain belt in the eastern part of my country will be carried northwards to the Huanghuai, North China, and northeast regions, and the cumulative rainfall will be 30% to 70% more than normal, and more than doubled in some areas. The main rainfall period is from 22 to 23 and around 26.

  “The South is making every effort to prevent floods and disasters, and the North cannot be sloppy.” Zhang Fanghua, chief forecaster of the Central Meteorological Observatory, said that in late July, rainfall in the northern region began to increase significantly, entering the critical period of the northern flood season in the "seventh and eighth" season. Especially the risk of secondary disasters caused by local heavy rainfall.

  What is "seven times and eight times"? Zhang Fanghua said that due to the influence of monsoon climate and topography, my country's rain belt moves from south to north every year. Normally, from late July to early August, the rain belt will be lifted from the north of the Yangtze River Basin to north China and northeast, and the north will enter the main flood season.

  Newspaper Beijing, July 13th

  China Youth Daily · China Youth Daily reporter Qiu Chenhui Source: China Youth Daily

  July 07, 2020 Version 07