Moisture Transfer Characteristics of Extreme Precipitation During the Warm Season in the Mid-south Section of the Taihang Mountains

Extreme precipitation events in China have increased significantly in recent decades. Extreme precipitation can easily trigger natural disasters such as urban waterlogging, landslides, and mudslides, which poses a serious threat to the social economy, human lives and property. Currently, research on extreme precipitation has attracted widespread attention.To increase the accuracy of extreme precipitation forecasts, precipitation data from automatic meteorological stations, ERA5 reanalysis data, and Global Data Assimilation System (GDAS) data are used to summarize the synoptic circulation affecting 75 extreme precipitation events in the mid-south section of the Taihang Mountains during the warm season (May-September) for the period of 2012-2021 on the basis of self-organizing maps (SOMs) neural network, synoptic verification method, and hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) model. Characteristics of moisture transfer and the resulting precipitation for various types of synoptic circulation are also discussed. Results show that there are five types of synoptic circulation that affect extreme precipitation during the warm season in the mid-south section of the Taihang Mountains, namely the upper trough type, low vortex type, zonal subtropical high type, meridional subtropical high type, and northwest airflow type. The upper trough type is the most frequent, accounting for 40.0%, while the northwest airflow type is the least common, representing less than 5%. The daily extreme, maximum hourly intensity, and impact range of precipitation resulting from the low vortex circulation are the highest among all types. There are three moisture transfer passages for the low vortex type: The Bay of Bengal, South China Sea, and Northwest Pacific. Compared to the low vortex type, the upper trough type cannot transfer moisture through the Northwest Pacific passage, while neither the zonal subtropical high type nor the meridional subtropical high type can transfer moisture through the Bay of Bengal passage. Air mass tracking results indicate that the contribution of moisture transfer from the Northwest Pacific is the highest for both the low vortex type and the zonal subtropical high type, the contribution of moisture transfer from the Yellow Sea coast is the highest for the upper trough type, and the contribution of moisture transfer from the South China Sea is the highest for the meridional subtropical high type. Analysis of the moisture budget in the whole troposphere reveals that the main moisture inflow of extreme precipitation during the warm season in the mid-south section of the Taihang Mountains comes from the southern boundary. Other inflow boundaries and the relative contribution of all inflow boundaries is related to the synoptic circulation. The moisture budget at the boundaries of the lower troposphere differs from that in the whole troposphere.