Phase- and Amplitude-Locking of Annual Maximum Rainfall Events in North China with the Annual Cycle of the East Asian Summer Monsoon

The annual maximum rainfall event (AMRE) refers to the maximum consecutive five-day rainfall in a year. In North China, these events account for 15%–80% of the total summer (June–August) rainfall amount and pose a great challenge for subseasonal-to-seasonal forecasting. Based on data analyses during 1979–2023, this study shows the interannual variability of AMRE is significantly influenced by the phase and amplitude mode of the annual cycle of the East Asian summer monsoon (EASM), characterized by two orthogonal patterns of southeasterly winds at 850 hPa over the northwestern Pacific. The EASM phase-locked AMRE shows heavy rainfall events occurring extremely early and late in Beijing and surrounding areas, corresponding to the peak southeasterly wind anomalies in June and August. The EASM amplitude-locked AMRE exhibits extreme heavy or light rainfall over southwest areas with normal phase. Therefore, AMRE has a potential predictability on the seasonal time scale due to its phase-locking with the slow variation of the annual cycle of the EASM.