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We use contingency tables to investigate the impact of the positive and negative phases of the PEO and SST (Niño 3.4) on the occurrence of the deficit and non-deficit runoff years, respectively. Table 3 shows the six contingency tables (for three rivers and two indices), where the contingency values are shown in percent from the lengths of the phase of the respective index. All the contingencies proved to be significant at the 95% confidence level (Chi-square test), except for the contingency between the occurrence of deficit/non-deficit years and the SST (Niño 3.4) phase in the Beijiang. It can be seen that deficit runoff years are contingent with the negative PEO phase and vice versa. In contrast, deficit runoff years are contingent with the positive phase of SST (Niño 3.4) and vice versa.

Table 3

Contingencies (%) between the runoff years (deficit/non-deficit) and the phases (positive/negative) of PEO and SST (Niño 3.4) with Cramér's V statistics (non-significant value shown in italics)

PEO
SST (Niño 3.4)
Year/PhasePositiveNegativePositiveNegative
Weihe 
 Deficit 25 75 57 43 
 Non-deficit 50 50 40 60 
 Cramér's V 0.52 0.34 
Beijiang 
 Deficit 37 63 37 63 
 Non-deficit 81 19 33 67 
 Cramér's V 0.94 0.09 
Qingjiang 
 Deficit 40 60 50 50 
 Non-deficit 75 25 29 71 
 Cramér's V 0.66 0.40 
PEO
SST (Niño 3.4)
Year/PhasePositiveNegativePositiveNegative
Weihe 
 Deficit 25 75 57 43 
 Non-deficit 50 50 40 60 
 Cramér's V 0.52 0.34 
Beijiang 
 Deficit 37 63 37 63 
 Non-deficit 81 19 33 67 
 Cramér's V 0.94 0.09 
Qingjiang 
 Deficit 40 60 50 50 
 Non-deficit 75 25 29 71 
 Cramér's V 0.66 0.40 

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