From July 29 to August 1, 2023, the North China region experienced a rare extreme rainstorm event (referred to as the “23.7” rainstorm), which triggered widespread flood disasters. This study systematically analyzed the water vapor transport characteristics and key driving mechanisms of this rainstorm based on ground meteorological station observation data, ERA5 reanalysis data, S-band Doppler radar data, and a qualitative Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The research results show that persistent southeasterly moisture transport from the Western Pacific Ocean and the South China Sea was strongly associated with sustaining the rainstorm in the Hebei region. This transport established a significant moisture convergence center, providing an abundant moisture source for the extreme precipitation. At upper levels, the southwest airflow formed around the western Pacific subtropical high strengthened vertical divergence over the rainstorm area. This pronounced upper-level divergence acted as a dynamic driver for deep ascent, maintaining the vertical circulation necessary to transport high- \(\theta_{e}\) air from the lower troposphere into the storm core, thereby prolonging the duration of heavy precipitation.During this rainstorm, the 55 dBZ strong radar echo centers of the convective system exhibited significant vertical development, extending into the upper troposphere. Although radar-derived heights serve primarily as qualitative indicators due to influences such as hydrometeor population, beam geometry, and attenuation effects, these elevated echo tops are consistent with the presence of exceptionally vigorous updrafts that facilitated the rapid lofting of hydrometeors and intensified surface rainfall. Additionally, trajectory simulations qualitatively identified the primary moisture transport routes for this heavy rainfall event. The primary driving mechanism behind the “23.7” rainstorm was the synergistic interaction among sustained and abundant horizontal moisture transport, intense vertical lifting within the storm region, and a robust upper-level divergence field. The dynamic coupling of these factors was strongly associated with prolonged convective activity. Moreover, a continuous moisture influx maintained a near-saturated thermodynamic profile, which significantly enhanced precipitation efficiency. Combined with the quasi-stationary nature of the system, this thermodynamic environment was critical in sustaining the massive rainfall totals. Further investigation into the triggering mechanisms of vertical water vapor transport is crucial for enhancing the forecasting capabilities of localized rainfall, particularly in mountainous regions, and for improving the accuracy of disaster risk assessment. This study advances the understanding of extreme precipitation formation mechanisms in North China, providing scientific support for optimizing numerical weather prediction models and strengthening early warning capabilities for extreme weather events.
