Analysis on the precipitation extremes of extremely heavy rainstorm event in Gansu Province of the '7·22' in 2024

The Hedong region of Gansu Province experienced the most severe regional torrential rain event From July 22 to 24, 2024, since 1961. This event was characterized by high cumulative precipitation, concentrated areas of heavy rainfall, prolonged duration, and intense convective precipitation. The epicenters of the torrential rain were located at the Xinyao Forest station in Chongxin County and the Longyang Checha station in Tongwei County, with a maximum cumulative precipitation of 367.7 mm. Using precipitation data from national and regional meteorological observation stations, as well as ground-radar-satellite three-source fusion precipitation analysis products, the precipitation characteristics and extremity of this regional torrential rain event were analyzed from perspectives such as precipitation intensity, duration, historical extremity, and the spatiotemporal evolution of heavy precipitation centers. The results are as follows. (1) This event exhibited significant convective characteristics, with high precipitation efficiency, long duration, and intense rainfall. A total of 456 stations recorded short-duration heavy rainfall, with the longest duration reaching 5 hours, contributing to ≥50% of the total precipitation. The representative stations in the torrential rain area showed that the cumulative precipitation over 3 hours accounted for approximately 59.02% of the total process precipitation, with maximum rainfall intensities of 8.9 mm·min⁻¹ and 79.1 mm·h⁻¹ per minute and per hour, respectively. The heavy rainfall at the two epicenters began in the northwest of Xinyao Forest station and the south of Longyang Checha station, oscillating in the east-west-south-north directions, and ended in the northeast of Xinyao Forest station and the southeast of Longyang Checha station. (2) During this event, 265 stations recorded process rainfall, 93 stations recorded short-duration heavy rainfall, and 91 stations recorded short-duration heavy rainfall durations exceeding the historical July extremes. The maximum daily precipitation at Chengxian, Chongxin, Jingning, and Tongwei stations were 182.9 mm, 232 mm, 125.2 mm, and 134.6 mm, respectively, all surpassing the maximum values since the establishment of the stations, approximately 1.4 times the average July precipitation. Additionally, indicators such as maximum daily precipitation, cumulative process precipitation, regional average heavy rainfall, number of stations with daily rainfall breaking records, duration of short-duration heavy rainfall, maximum 1-hour precipitation, and comprehensive intensity index all exceeded the maximum values of other regional torrential rain events since 1961.