Abstract:Based on surface and radiosonde observations in China and ERA5 reanalysis data, the characteristics of water vapor transport, budget and extremity of the severe torrential rain in North China from 29 July to 1 August 2023 (referred to as the “23·7” event) and the important role of the terrain of the Taihang Mountains in persistent moisture convergence and vertical transportation are studied. The results show that this extreme torrential rain event occurred in the north of the residual vortex of Typhoon Doksuri, obstructed by a high pressure barrier, and with the favorable background of water vapor transport by two typhoons Doksuri and Khanun. The event had significant extreme features in its long duration, intense daily precipitation and enormous accumulated rainfall amount. The low-level strong southeast jet stream continuously transported water vapor to North China. The southern and eastern boundaries of the torrential rain central area were both net inflow of water vapor, especially the southern boundary. The easterly wind was forced to lift in the high gradient area of the terrain height at the eastern foot of the Taihang Mountains, forming a strong water vapor convergence and vertical transport center, and maintaining the state stably, which was an important cause for this severe torrential rain event. The maximum of precipitable water exceeded 75 mm and the normalized value exceeded 3.0. The comparison results also indicate that the low-level water vapor source in the “23·7” event was quite different from another severe torrential rain that occurred on 19-20 July 2016 in North China. The former had the water vapor source mainly from the Northwest Pacific Ocean and the South China Sea, while the water vapor of the latter was mainly from the South China Sea and the Bay of Bengal. Besides, the average water vapor convergence in the former was significantly weaker than that in the latter, and the number of short-time severe precipitation stations was also less than the latter, but the duration of the former was longer. This indicates that compared to the intensity of precipitation, the prolonged duration was a more critical factor in producing this severe torrential rain.