Disastrous Persistent Extreme Rainfall Events of the 2022 Pre-Flood Season in South China: Causes and Subseasonal Predictions

Two persistent extreme rainfall events (PEREs) with record-breaking amounts of rainfall and long duration caused disastrous impact during the 2022 pre-flood season in South China. Atmospheric intraseasonal variability played a key role in triggering and maintaining both PEREs, but its major impact on each event was associated with different modes. For the first PERE (10‒15 May; PERE1), the tropical and extratropical quasi-biweekly oscillations jointly contributed to the extreme rainfall intensity. In contrast, the long duration (6‒21 June) of the heavy rainfall during the second PERE (PERE2) was closely related to prolonged convection and moisture transport anomalies induced mainly by the tropical 30‒90-day variability. Subseasonal-to-seasonal predictions by the model of the ECMWF showed limited skill in relation to the rainfall intensity of PERE1 and PERE2 beyond 1–2 weeks. Further assessment suggested that the fidelity of the PERE predictions was linked to model skill in predicting the phase evolution and intensity of tropical and extratropical intraseasonal variabilities. Thus, efficient monitoring and accurate prediction of the various modes of atmospheric intraseasonal variability are fundamental to reducing the hazard associated with PEREs in South China.