Relative Contribution of Moisture Transport during TC-Active and TC-Inactive Periods to the Precipitation in Henan Province of North China: Mean State and an Extreme Event

A Lagrangian model}the Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT)}is used to quantify changes in moisture sources and paths for precipitation over North China’s Henan Province associated with tropical cyclone (TC) over the western North Pacific (WNP) during July–August of 1979–2021. During TC-active periods, an anomalous cyclone over the WNP enhances southeasterly and reduces southwesterly moisture transport to Henan. Accordingly, compared to TC-inactive periods, moisture contributions from the Pacific Ocean (PO), eastern China (EC), and the local area (Local) are significantly enhanced by 48.32% (16.73% versus 11.28%), 20.42% (9.44% versus 7.84%), and 2.89% (4.91% versus 4.77%), respectively, while moisture contributions from the Indian Ocean (IO), Southwestern China (SWC), Eurasia (EA), and the South China Sea (SCS) are significantly reduced by 231.90% (8.61% versus 12.64%), 216.27% (4.60% versus 5.50%), 28.81% (19.10% versus 20.95%), and 26.92% (12.18% versus 13.09%). Furthermore, the moisture transport for a catastrophic extreme rainfall event during 17–22 July (“21?7” event) influenced by Typhoon Infa is investigated. Compared to the mean state during TC-active periods, the moisture contribution from the PO was substantially increased by 126.32% (37.87% versus 16.73%), while that from IO significantly decreased by 298.26% (0.15% versus 8.61%) during the “21?7” event. Analyses with a bootstrap resampling method show that moisture contributions from the PO fall outside the 16s range, for both the TC-active and TC-inactive probability distributions. Thus, the “21?7” event is rare and extreme in terms of the moisture contribution from the PO, with the occurrence probability being less than 1 in 1 million times.