Quantitative contribution analysis of moisture sources to the "23·7" extreme heavy rainfall in North China

Using the Lagrangian particle dispersion model FLEXPART (the Flexible Particle Model) and the quantitative contribution analysis method of moisture sources, the main moisture source areas, transport paths, and quantitative contributions of moisture sources to the "23·7" extreme heavy rainfall in North China along with their temporal variations are studied. Six main water vapor source regions are identified. The largest total water vapor uptake equivalent to 1.93 times the accumulated precipitation amount over the target area came from the Western Pacific Ocean (E), followed by that from the Arabian Sea-Bay of Bengal region (D) and the southern China region (C), where the water vapor uptakes were 0.96 and 0.76 times of precipitation over the target area, respectively. The target area (T, 0.30 times), the northeastern Asian continental region outside the target area (B, 0.28 times) and the Eurasian continental region (A, 0.01 times) showed successively decreasing total water vapor uptake. During the initial phase, influenced by the cross-equatorial airflow and the subtropical high, regions D and E were the primary sources of water vapor uptake, accounting for more than 90% of the total. In the middle phase, air masses from region D moved into region E and merged into the circulation of tropical cyclone Doksuri, leading to a decrease in water vapor uptake in region D and a significant increase in region E. Prior to the onset of the process, as Doksuri made landfall in region C, the water vapor uptake in region C peaked. Ultimately, the total contribution of all the source regions to precipitation in the target area reached 95.34%, with region E (43.10%) and C (26.47%) being the main contributors. Regions D (12.26%) and T (11.85%) also had significant impacts while regions B (1.58%) and A (0.08%) had minor contributions. Tropical cyclone Doksuri had a notable effect on the movement of air masses and water vapor uptake, and the direct impact of tropical cyclone Khanun on this process was relatively small.