Contributions of Large-Scale Circulation and Local Land–Atmosphere Interaction to Precipitation in Eastern China: Investigation on Influencing Factors of the July 2021 Heavy Precipitation Event in Henan Province

A record-breaking precipitation event happened in Henan Province in July 2021, which caused great casualties and economic losses. During the flood season in eastern China, this event exposed some deficiencies in precipitation prediction. The ERA5 reanalysis product and a dynamic adjustment (DA) approach were applied in this study to explore the contributions of large-scale circulation and local land–atmosphere interaction in this extreme precipitation event. The 500-hPa geopotential height constructed circulation analogs were used in DA to separate the effects of large-scale circulation dynamics and local land surface effects on precipitation anomalies in eastern China from 1979 to 2021. Finally, the contribution of these two effects to the extreme precipitation event is quantified. The following are the main conclusions: The year 2011 had a 500-hPa circulation similar to July 2021, while the corresponding precipitation fields showed significant differences from North China to the Yangtze River’s middle and lower reaches. After DA, the influence of atmospheric circulation is separated from precipitation anomalies. The correlation analysis shows that the residual component of precipitation anomaly reflects local land–atmosphere feedback. The residual is the main cause of the anomalous heavy precipitation from the Jianghuai region to the lower reaches of the Yangtze River in July 2021. Attribution analysis shows that the residual component is mainly caused by the change in local thermal factors: enhanced evaporation reduces sensible heat flux and increases precipitation by affecting atmospheric relative humidity and boundary layer height. Among them, evaporation is strengthened, sensible heat flux is significantly reduced, the unstable energy of strong atmospheric convection is increased, and precipitation is increased by influencing atmospheric relative humidity and boundary layer height. When the precipitation evolution process is extended from 1979 to 2021 in July, it is found that the interannual variability of the residual precipitation component is very strong, the extreme precipitation anomaly is mainly reflected in the residual component, and the circulation component is relatively stable. The results emphasize the important influence of the local thermal effect on extreme summer precipitation. This study shows that taking into consideration both the characteristics of large-scale atmospheric circulation and the contribution of local thermal effects is necessary to improve the prediction of summer precipitation in eastern China, and the latter is particularly important to the prediction of extreme summer precipitation.