What Caused the Differences between “23·7” and “96·8” Extreme Rainfall Events in North China under a Similar Synoptic Background?

This study examined the rainfall characteristics and related synoptic processes of two extreme rainfall events that affected North China during 29 July to 1 August 2023 (“23·7” rainstorm) and 3–5 August 1996 (“96·8” rainstorm). A stable dual-typhoon circulation pattern was observed at the time of occurrence of both rainstorms. The surviving vortex of a landed typhoon, slowly approaching the rainstorm region, was blocked by a high-pressure system as it moved northwestward. Meanwhile, the second typhoon over the western Pacific Ocean facilitated remote transport of moisture northward. The low-level jet between the surviving vortex and the western Pacific subtropical high relayed moist warm air from the area of the South China Sea and western Pacific into the rainstorm region. Although the circulation patterns are similar, the stratification conditions, driving factors, and moisture budget of the two rainstorms differed during the main period of rainfall. The “23·7” rainstorm was categorized as warm-sector rainfall, resulting from the lifting of warm moist air over the eastern foothills of Mt. Taihang. In comparison with the situation of the “96·8” rainstorm, the surviving vortex of the “23·7” rainstorm traveled further northeastward, directly impacted the occurrence and progression of the rainfall, leading to relative northward displacement of the rainfall center, while the stronger net inward moisture flux caused the greater region-averaged rainfall. The “96·8” rainstorm was broadly analogous to precipitation of a cold front, and the rainfall center occurred in the area of converging warm and cold air masses before the mountains; the surviving vortex did not exert direct impact on the rainfall; and the more unstable stratification led to stronger hourly rainfall. The results derived through comparison of the two rainstorms could serve as valuable scientific reference for operational forecasting of heavy rainfall under similar environmental conditions over North China.