Markov Chain Analysis of Rainfall over East Asia: Unusual Frequency, Persistence, and Entropy in the Summer 2020

Record-breaking rainfall occurred over East Asia during the summer of 2020. However, in which aspect the summer of 2020 can be differentiated from the other years remains to be quantified. To this end, this study employs Markov chain analysis to quantify summer rainfall variability over East Asia using three Markov descriptors for heavy precipitation events of over 10 mm day⁻¹: frequency, persistence, and entropy (i.e., irregularity). It is found that the heavy rainfall during the summer of 2020 can be attributed to an anomalously high frequency of rainfall in the central China and Japan and greater rainfall persistence over eastern China and Korea. Empirical orthogonal functions (EOFs) are used to analyze interannual variation in the descriptors using a few primary modes. For the summer 2020 period, the first and second modes for frequency account for the enhanced frequency over central China, and this is linked to sea surface temperature anomalies over the North Pacific, the equatorial eastern Pacific, and tropical Indian Ocean. For persistence, the first mode dominates the anomalous rainfall persistence observed during the summer of 2020. Similar but weak behavior can be also seen by the modes for entropy.