Abstract:Based on the precipitation and temperature data of national stations in China, NCEP/NCAR reanalysis and sea surface temperature data, the features and possible causes of climate anomalies in spring 2021 (March-April-May) in China are analyzed in this paper. In 2021, China experienced the fourth warmest spring since 1961 with an average temperature anomaly of 1.2℃, except that Central China was cooler than normal in April. The precipitation was near normal with a national average of 145.3 mm, but which the sub-seasonal periodic variation was quite significant, which is closely related to the periodic adjustment of circulation. From March to April, the mid-latitude circulation over Asia maintained an anomalous pattern of positive geopotential height (GPH) anomalies in the east of Lake Baikal but negative anomalies over the Ural Mountains. The Western Pacific subtropical high (WPSH) was weaker and further eastward than normal, which was conducive to water vapor transportation from the Northwest Pacific to the north of the Yangtze River, resulting in more precipitation in northern China but less precipitation in South China and Southwest China. However, the above patterns reversed in May, with positive GPH anomalies over the Ural Mountains and negative anomalies in Northeast Asia as well as the intensified and further northwestward WPSH. Correspondingly, the warm and humid southwesterly flow at lower-level strengthened, and the water vapor convergence and upward movement developed in southern China. This pattern was favorable for less precipitation in northern China while more precipitation in southern China, especially for frequent heavy rainstorms and severe convective weathers in the regions south of the Yangtze River. From mid-April, blocking activities in mid-high latitudes occurred frequently, causing a low-temperature anomaly in central China temporarily, and also becoming one of the important factors for the severe convective weather in southern China. The adjustment of atmospheric circulation in late spring is related to the interaction between high and low latitude circulation and the tropical SST evolution. In mid-April, the Arctic Area warmed up and the high ridge over the Ural Mountains strengthened, resulting in the above circulation transition in late spring. Meanwhile, with the rapid warming of the tropical Inian Ocean in May, the low latitude circulation situation in East Asia responding to the La Ni〖AKn~D〗a Event in the early stage was also significantly adjusted, thus leading to the significant variation in the distribution of sub-seasonal precipitation.