Comparison of Heavy Rainfall Events Originated from Different Directions of Beijing City

Strong rainfall events originated from the northeast (NE) and southwest (SW) directions of the plain area of Beijing City (BJP) over 8 recent warm seasons (May–September of 2009–2016) were analyzed by using hourly merged rainfall, satellite brightness temperature, and the fifth-generation ECMWF reanalysis (ERA5) data. Such heavy regional rainfall events (RREs) with different origins present quite different features in both the precipitation itself and its corresponding circulations. The heavy RREs originated from the SW occur more frequently in the flood season of North China (July and August), and the peak time of rainfall occurrences is in the early morning. They are linked with stronger large-scale circulation forcing, compared with the NE-originated events. Meanwhile, the ratio of heavy rainfall to the total rainfall in SW-originated events, the mean spatial coverage of rainfall, and associated convective index, are also larger, for the SW events. The heavy RREs from the NE occur more frequently in June and July (before the traditional flood season), with a more apparent afternoon peak. They exhibit stronger convective features, with higher maximum convective index values, but the large-scale forcing is weaker at the hour of onset. These features of the RREs from different directions of Beijing City and associated precursor circulation signals help better forecast RREs over the BJP.