Why is there so much rain in the north this year?
This is closely related to the anomaly of subtropical high.
In June, the heavy precipitation mainly occurred in the south. In July, the subtropical high moved northward earlier than normal, and its intensity was stronger. The warm and humid airflow from the southeast guided by its periphery was transported to the north, which led to the early start of the rainy season in North China. Due to the strong subtropical high in the north, the eastward movement of the upper trough and the low vortex system, two extra-strong precipitation processes occurred in the north.
The first time was an extremely heavy rainfall process in North China and Northeast China from July 11th to 13th. Heavy rain occurred in Beijing-Tianjin-Hebei, southeastern Shanxi, northern Henan, north-central Shandong, southern Liaoning and other places. The daily rainfall of seven national meteorological observation stations in Hebei and Henan exceeded the maximum in July, among which Jize in Hebei (26.4 mm) exceeded the historical maximum since meteorological records were recorded.
The second time was from July 17th to 22nd. In addition to the situation mentioned above, the precipitation system moved slowly due to the water vapor transport support of the typhoon "Fireworks" and the blocking of the high-pressure dam on the east side, and the accumulated rainfall in Henan, Shanxi and Hebei was extremely alarming.
Among them, the largest cumulative rainfall occurred in qibin district, Hebi City (1122.6 mm). During the rainfall, the daily rainfall of 2 national weather stations in Zhengzhou, Xinxiang, Hebi and Anyang * * * exceeded the historical extreme since the establishment of the stations. The maximum hourly rainfall of Zhengzhou Meteorological Observatory reached 21.9 mm (from 16: to 17: on the 2th), which exceeded the historical maximum of hourly rainfall in Chinese mainland (198.5 mm in Linzhuang, Henan on August 5th, 1975).
in August, the subtropical high is stronger to the west, and the circulation in the westerly belt at middle and high latitudes fluctuates frequently, causing continuous rainfall and more convective weather, which leads to more precipitation in many places in the north in August. By the end of August, the subtropical high had retreated southward, and the autumn rain in West China started ahead of schedule, and it was threatening. For example, Wanyuan in the northeast of Sichuan, the cumulative rainfall from August 23rd to September 22nd reached 647mm, the highest in the same period since 1951.
in big cities, the rainfall at many stations has exceeded the extreme value. Data show that from June 1 to September 22, the accumulated rainfall in Zhengzhou, Henan Province (1318 mm), Haidian, Beijing (163.5 mm) and Jinzhou, Liaoning Province (87.7 mm) was the highest since 1951, of which the rainfall in Zhengzhou was more than twice that recorded in the same period before, and the rainfall in Jinzhou was about twice as high as that in normal years.