Xinhua News Agency, Beijing, July 21st
Question: What is the climate trend of “seven downs and eight ups” in the rainy season in North China?
Xinhua News Agency reporter Huang Yao
Beginning at night on the 20th, rainfall in North China gradually increased. Meteorological monitoring shows that heavy to heavy rains occurred in western Beijing and central Hebei, and heavy rains fell in Hengshui, Baoding, and Shijiazhuang in Hebei. According to the forecast of the meteorological department, this round of rainfall will continue until the 23rd, and North China has entered the rainy season.
What month does the rainy season usually fall in North China? What are the characteristics of my country’s weather and climate this year?
In fact, with the movement of the rain belt, the time of the rainy season in various parts of our country is also different. May to June is the rainy season in the south of the Yangtze River, June to July is the rainy season in the Jianghuai area, July is the rainy season in Huanghuai and North China, August is the northeast rainy season, and September to November is the autumn rain in West China. From late July to early August every year, the rain belt in eastern my country moves north to North China and Northeast China, reaching the northernmost position of the year. During this period, North China and Northeast China usher in a period of concentrated precipitation, commonly known as “seven downs and eight ups”.
Around the end of July, the northern edge of the summer monsoon pushed forward to North China, and at the same time, the western Pacific subtropical high-pressure ridge moved northward to the area north of 30°N latitude. The southwest airflow or easterly airflow on its west side continuously transported the water vapor on the ocean surface to the north, providing sufficient water vapor conditions for rainfall in North China. Once the warm and humid air meets the cold air moving eastward and southward, it is easy to bring heavy precipitation to the northern regions. During the “seven downs and eight ups” period, the northern region reaches the maximum rainfall peak, and the precipitation in one month may account for one-third of the whole year.
In many public impressions, heavy rains in North China are concentrated and intense. This is because North China is located in the mid-latitude temperate monsoon region, and the heavy rain season is concentrated in summer. Additionally, the special terrain such as the Taihang Mountains lifts water vapor and warm and humid air, making heavy rainfall more likely to occur.
Gao Hui, chief forecaster of the National Climate Center, said that the start of the rainy season in North China this year is later than normal. It is expected that the rainfall in the rainy season in North China this year will be close to normal, but there will be differences in spatial distribution. The precipitation in the eastern part of North China may be higher than normal, while that in the western part may be less.
“Seven downs and eight ups” is a critical period for flood control in our country. During this period, the north enters the main rainy season; at the same time, typhoon activities in the South China Sea and the western Pacific Ocean enter an active period, and coastal areas are vulnerable to typhoon precipitation and storm surges.
According to the forecast of the National Climate Center, during this year’s “seven downs and eight ups” period, my country’s drought and floods will be equal. The precipitation in the eastern part of the Songhua River Basin and the eastern part of the Liaohe River Basin will be more than 20% higher than that in the same period of normal years, and severe floods and flood disasters may occur; the western Songhua River Basin, Nenjiang River Basin, and western Liaohe River Basin need to pay attention to local flood disasters that may be caused by periodic heavy precipitation processes. At the same time, the temperature in most parts of my country is close to the same period of normal years to high, and the number of high-temperature days (daily maximum temperature ≥ 35°C) in most of North China, southeastern China, central and southern China, and Xinjiang is higher than that of the same period of normal years, and there is a greater possibility of periodic high-temperature heatwaves. The number of tropical cyclones (typhoons) expected to land in my country is 2 to 3, and the average intensity is relatively strong, mainly affecting South China and the southeast coast.
Experts said that all localities and departments should pay close attention to the floods of small and medium-sized rivers and the safety of small and medium-sized reservoirs, and carefully implement preventive and countermeasures to guard against sudden changes in drought and floods. The public should always pay attention to the latest weather forecast and warning information issued by the local meteorological department, learn relevant defense knowledge in advance, and stay away from dangerous areas during heavy rain.
[责编：袁晴]