Comparative analysis of synoptic characteristics and causes of regional persistent extreme precipitation events over North China Plain between the year of 2021 and historical years

The variability of regional persistent extreme precipitation events (RPEPEs) is increasing in many regions and globally. Under the decreasing climatic trend since 1990s, North China Plain (NCP) has experienced extremely strong and more occurrence but unevenly distributed RPEPEs in the year of 2021. Influenced by multi-scale systems ranging from planetary, synoptic and sub-synoptic scales together with sea-air interactions, precipita-tion features for 2021 and their anomalies to historical events are complicated. Regional differences of precip-itation features over different subdomains of NCP are investigated first. It is found that the southern subdomain presents significantly extremes in precipitation features in 2021. The dominant responsible synoptic system at upper-middle troposphere is the low pressure in the westerlies which locates east and south to the historical average to the extent of 10 degrees. The stronger western Pacific subtropical high is also significantly south to the historical one. The location of the water vapor source in 2021 is 30 longitudes to the east and 5-10 latitudes to the north, bringing water vapor amounts about 1.5 times more than in historical events. The induced vertical closed circulation anomaly further triggers the positive feedback favor for the occurrence, persistence and intensification of RPEPEs. Regional differences of precipitation features over NCP in 2021 are especially evident in its southern subdomain which are mainly resulted from configuration of circulations and their induced intensified water vapor transports. The standardized anomaly method is used in this study to separate the his-torical RPEPEs and the ones in 2021 into different categories from the perspective of synoptic circulation backgrounds. Similarities and differences in precipitation features and circulation characteristics between meridional and zonal types are further investigated through comparative analyses. The specific synoptic reasons for each category in 2021 with comparisons to their historic correspondence are also concluded in this study.