Analysis of "21 . 7" extreme rainstorm process in Henan Province using BeiDou/GNSS observation

Influenced by severe typhoons "In-Fa" and "Cempaka", an extreme rainstorm occurred in Henan Province in July 2021, which caused heavy casualties and huge economic losses. The process of extreme rainstorms is complex, and the precipitable water vapor (PWV) is one of the main factors of its occurrence. Understanding the relationship between the occurrence process of extreme rainstorms and PWV is of great significance for the short-term forecast of rainstorms. Based on the observations from 220 continuously operated BeiDou/GNSS stations in Henan Province, the spatial gridded PWV data with a high spatial and temporal resolution during the extreme rainstorm in Henan Province were obtained using precise point positioning (PPP) technology and Kriging interpolation method. The relationship between PWV variation and precipitation of the extreme rainstorm was analyzed from temporal and spatial scales based on the precipitation data from 116 meteorological stations. Results showed that the root mean square (RMS) of the PWV difference between the BeiDou/GNSS stations obtained by the PPP and the global meteorological reanalysis data ERAS is 3.2 mm. Furthermore, the spatial gridded PWV data obtained by the Kriging interpolation method has an RMS of 4.6 mm compared with the radiosonde, and an RMS of 4.4 mm compared with the ERAS. This indicates that the accuracy of the PWV data in this paper could meet the requirements of meteorological research. By analyzing the time series of hourly PWV and precipitation at BeiDou/GNSS stations and the adjacent meteorological stations, it shows that the PWV reaches a high level during the rainstorm, and the PWV generally increases sharply 1 similar to 3 hours before the occurrence of the extreme precipitation. Through the analysis of the spatial distribution relationship between PWV and precipitation, it manifests that the corresponding precipitation intensity is generally higher for regions where the PWV is higher.