Modulation of PDO on the predictability of the interannual variability of early summer rainfall over south China

This study investigates the modulation of the Pacific Decadal Oscillation (PDO) on the predictability of interannual early summer south China rainfall (SCR) using high-quality station rainfall data. Of particular interest is the difference in impact between negative and positive phases of the PDO on the predictability of interannual early summer SCR. A clear difference in the correlation between the interannual early summer SCR and the preceding sea surface temperature (SST) over the Pacific Ocean appears in negative and positive phases of the PDO. In the negative PDO phase, the correlation between interannual early summer SCR and SST is dominated by a pattern with significant negative correlations in the subtropical western North Pacific and southeast Pacific and significant positive correlations in the tropical central Pacific. However, in the positive PDO phase, significant positive correlations are observed in the tropical eastern Pacific. It is found that, for each PDO phase, the preceding SST anomalies in some regions in the Pacific may act as predictors of the interannual early summer SCR. As such, a two-regime regression model for the relationship between interannual early summer SCR and preceding SST anomalies is established based on the negative and positive PDO phases using respective multiple linear regression models. Results suggest that the interannual early SCR is more predictable in PDO positive phase than in negative phase. It offers a support for the argument that a segmented statistical forecasting approach associated with the decadal modulation effect of the coupled ocean atmospheric mode should be adopted to forecast the early summer SCR.