Comparative analysis of the water vapor paths and sources for different heavy rainfall regions during Typhoon Lekima (1909)

As water vapor is essential for typhoon precipitation, exploring its origins is of great

physical importance for understanding the evolution of these precipitation events. The differences and their causes of water vapor paths and contribution of two centers of precipitation in Zhejiang and Shandong during Typhoon Lekima are analyzed by Hybrid Single-Particle Lagrangian Integrated Trajectory model (HYSPLIT) which is driven by the data from the fifth generation atmospheric reanalysis data of the European Center for Medium-Range Weather Forecasting, and using the areal source receptor attribution method. The results show that: (1) there are four main moisture paths responsible for precipitation in Zhejiang, respectively from the eastern Pacific Ocean, Australia, the western Pacific Ocean and the Indian Ocean, while there are three main moisture paths for precipitation in Shandong, respectively from the eastern Pacific Ocean, the Indian Ocean and the western Pacific Ocean, with the proportion of the eastern Pacific path increasing to 51.7%. The main reason for the difference of the water vapor path is related to the weakening of the south-westerly wind, which led to a reduction in trajectories from the Indian Ocean and Australia, while the easterly wind in the north of the two typhoons increased the proportion of Pacific transport pathways. (2) Regarding water vapor contribution, the primary source regions for Zhejiang are the Pacific (33.1%) and Australia (15.3%), mainly due to the high trajectory frequency and high moisture conversion rates from these regions. The water vapor contribution from the Pacific Ocean is the highest for the precipitation in Shandong, reaching 73.8%, which is attributed to the high trajectory frequency and the high moisture uptake ratio of 80.8% among air parcels from the Pacific Ocean. Therefore, water vapor pathways and sources vary across different stages of the same typhoon. These findings can enhance the understanding of water vapor sources and provide valuable references for predicting precipitation locations during typhoon events.