The influence of solar activity and ENSO variability on epidemic outbreaks in Ming-Qing period

The multiscale temporal characteristics of epidemic evolution and their relationship with climate variability remain inadequately elucidated. To clarify the multiscale temporal variability and underlying mechanisms governing epidemic outbreaks during the Ming-Qing period, we applied the Complete Ensemble Empirical Mode Decomposition (CEEMD) method to decompose epidemic intensity series. This decomposition revealed pronounced variations at annual, inter-decadal, and centennial scales, corresponding to eight distinct periodic components of 3, 7, 16, 33, 75, 292, 511 and 844 years. Significantly, the contribution rate of epidemics peaked at the annual scale, reaching 66.52% in total, indicating the high frequency of epidemic occurrences during this period. Moreover, annual to inter-decadal epidemic fluctuations exhibited synchronization with ENSO variability. Comparative analysis and cross-spectral analysis further identified significant synchronous variations and shared periodic components between epidemic evolution and ENSO, indicating that regional hydrological change controlled by ENSO primarily drove epidemic patterns during the Ming-Qing period. On longer inter-decadal and centennial scales, the periodic components identified by CEEMD demonstrated remarkable alignment with solar activity cycles. This finding demonstrates that solar activity modulates regional temperature and precipitation through an air-sea coupling amplification mechanism, thereby governing epidemic outbreaks. Against the backdrop of contemporary global warming and projected intensification of ENSO variability, the risk of epidemic occurrence and spread may substantially increase in the near future.