El Niño event has a significant impact on global climate, especially on regional droughts and floods, being an important source of signals for climate prediction. In order to understand the impact of El Niño on summer droughts and floods in North China,based on the monthly precipitation data of ore than 2 400 stations from 1961 to 2022, the monthly sea surface temperature data reconstructed by NOAA and the reanalysis circulation data from NCEP/NCAR, this paper comprehensively studies the relationship between interannual variability of El Niño and summer droughts and floods in North China and its impact mechanism by using seasonal evolu⁃tion empirical orthogonal function decomposition (SEOF), regression reconstruction of circulation anomalies, circulation composition analysis. The main results are as follows: (1) There is a significant negative correlation between the summer precipitation in North China and the El Niño state in summer of the current year. That is, El Niño begins to appear in the spring, develops in the summer and has a strong intensity, which results in less summer precipitation in North China and is prone to drought. Further analysis shows when the La Niña states in spring, summer, autumn and winter in the previous year change to El Niño states in spring, summer, autumn and winter in the current year, the summer precipitation in North China is significantly less and prone to drought. (2) El Niño affects summer precipitation in North China mainly by regulating the high and low level circulation. The circulation patterns of the 200, 500 and 850 hPa induced by El Niño in the summer of that year are consistent with the circulation patterns of the drought summer years in North China. (3) When the upper westerly jet at 200 hPa over North China and its north side is weak, the ascending motion caused by upper air disturbance will be obviously weak. The position of the western Pacific subtropical high at 500 hPa is southward, and North China is controlled by a circulation pattern of “high in the west and low in the east”. The low trough system moves eastward at a fast speed, which is not conducive to maintaining long-term precipitation processes in North China. The tropical Indian summer monsoon and the East Asian subtropical summer monsoon at 850 hPa are relatively weak, and North China lacks effective sources of water vapor transport. This high and low level circulation configuration will result in less precipitation in summer in North China, making it prone to drought. 

In order to deeply understand the causes of the abnormal drought and high temperature climate event in the Yangtze River Basin in summer 2022 and improve the climate prediction technology, this paper makes a comprehensive analysis from the perspective of atmospheric circulation anomaly by using temperature and precipitation data from more than 2400 observation stations and NCEP/NCAR reanalysis circulation data from 1951 to 2022, and using T-N wave activity flux, apparent heat source Q₁ (Q₂) diagnosis and composite analysis, anomaly analysis and other methods. The main conclusions are as follows: (1) In summer of 2022, the disturbance originating from the North Atlantic region was unusually strong at 500 hPa, triggering an obvious large trough and ridge activity when it was propagating eastward along the mid-and high-latitude westerly belt. The wave energy mainly propagated eastward along the westerly belt, without the characteristic of propagating southeastward in East Asia, resulting in the northward location of cold air activity, which hardly affected the Yangtze River Basin. (2) In summer of 2022, the 500 hPa height field showed a significant positive anomaly disturbance over the Qinghai-Tibet Plateau region, which further strengthened in August and moved eastward to the Yangtze River Basin, inducing the westward extension of the Northwest Pacific subtropical high, making the subtropical high appear as an east-west zonal distribution. The western part of the subtropical high completely controlled the Yangtze River Basin area. On the one hand, the subtropical high blocked the cold air from the north to the south, on the other hand, the subtropical high maintained the sinking movement for a long time, which was not conducive to precipitation and conducive to sinking and warming. (3) In summer 2022, the location of the tropical convection area (apparent heat source) was abnormally south to the south of the equator (the climate state is between 5°N and 20°N), which has two impacts: one is to cause the ascending branch of the Hadley meridional circulation (Hadley Cell) to be anomalously southward, and the Yangtze River Basin was an anomalous sinking area in August, which is not conducive to precipitation and conducive to the appearance of the sinking warming effect. The other is to cause the weak Asian tropical summer monsoon and strong East Asian subtropical summer monsoon in summer 2022, and the low-frequency signal propagation to the middle and lower reaches of the Yangtze River was obviously weak, which are unfavorable to precipitation process in the middle and lower reaches of the Yangtze River. (4) The synergistic effect of three circulation anomalies in the high latitudes, mid-low latitudes, and the tropics caused an anomalous drought and high temperature climate event in the Yangtze River Basin in summer of 2022. To predict the summer precipitation or high temperature and drought in the Yangtze River Basin, it is necessary to pay attention to the occurrence and future propagation characteristics of the disturbance signal at 500 hPa in the North Atlantic region, the occurrence and movement characteristics of the 500 hPa height field disturbance over the Qinghai-Tibet Plateau, the changes in the location of the tropical convective region (heat source) and the accompanying changes in the intensity of the tropical summer monsoon, and the propagation characteristics of low-frequency signal in advance.