Analysis of the Synergistic Effect of Water Vapor, Thermodynamics, and Dynamics of the Heavy Rainfall Over Henan Province, China in July 2021

Abstract

During July 19–21, 2021, Henan Province in China experienced a historically rare heavy rainfall event, with the maximum hourly rainfall amount appearing in Zhengzhou City, the capital of Henan Province, on 20 July (hereafter “7.20” HRE). In this study, the “7.20” HRE is analyzed based on the observations of 215 ground-based GNSS stations and 118 national meteorological stations in Henan Province, and ERA5 reanalysis data. By comparing the surface precipitation intensity, water vapor, and atmospheric energy conditions across temporal and spatial scales, it is shown that the area with heavy rainfall near Zhengzhou did not exhibit extreme atmospheric energy values or vertical environmental instability. The environmental conditions in the southeast of Zhengzhou were more conducive to the occurrence and development of precipitation, but there was no obvious precipitation on the ground. The analysis of water vapor consumption rate (V_c) and precipitation flux (F) reveals that a large amount of water vapor was consumed in the southeast of Zhengzhou, resulting in the formation of substantial precipitation above the 600 hPa level. The precipitation was carried to Zhengzhou by the southeast wind, leading to the precipitation content over Zhengzhou and its nearby areas increasing rapidly as altitude decreased from 600 hPa to 1000 hPa. The overlay of precipitation provided by both dynamic transport from the southeast and cloud microphysical production over Zhengzhou was the main cause of the “7.20” HRE under the background of an atypical weak environmental field.