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Table 6 shows that future annual runoff depth of all three watersheds is inclined to rise slightly relative to the baseline level, with a higher level of runoff increase under the QQDC-A1B scenario. The paired-sample Wilcoxon signed-rank test (Table 6) confirms that both the SDC-A1B and QQDC-A1B annual runoff depths are significantly greater than the baseline runoff at a 5% significance level and that the QQDC-A1B annual runoff has a slightly higher increase in runoff. This phenomenon can very likely be attributed to the fact that the QQDC method tends to project mildly higher annual precipitation in the Pearl River basin compared with the SDC method. With respect to the variability of annual runoff, both the simulated SDC-A1B and QQDC-A1B annual runoff display a minor increase in standard deviation than the baseline, but the CVs of these three annual runoff time series do not change significantly. In addition, the first, second, and third quartiles (Q1, median, and Q3) as well as the maximum annual runoff in SDC-A1B and QQDC-A1B show an overall increase over the baseline level, indicating more high-flow years in the future.

Table 6

Statistical properties of simulated annual runoff depth in the baseline, QQDC-A1B, and SDC-A1B scenarios

Runoff quartiles (mm)
Paired-sample Wilcoxon signed-rank test
WatershedsDataMean (mm)SD (mm)CVMinQ1MedianQ3Maxzcalzcrip-value
Wuxuan Baseline 633.4 117.3 0.185 367.6 559.4 645.4 711.5 902.8    
SDC-A1B 688.7 122.7 0.178 417.9 616.2 694.1 785.3 945.0 a4.772> 1.64c 0.0000 
QQDC-A1B 696.4 128.8 0.185 427.4 606.9 695.0 778.8 956.7 b2.057> 1.64c 0.0192 
Shijiao Baseline 1,015.7 263.5 0.259 385.8 845.1 959.5 1,113.9 1,620.5    
SDC-A1B 1,093.6 286.8 0.262 360.3 910.3 1,071.4 1,239.4 1,776.4 a4.463> 1.64c 0.0000 
QQDC-A1B 1,149.2 306.1 0.266 383.7 944.8 1,101.6 1,252.2 1,887.4 b4.648> 1.64c 0.0000 
Boluo Baseline 967.4 241.5 0.250 357.6 836.8 945.2 1,082.7 1,573.7    
SDC-A1B 1,029.4 241.4 0.235 375.9 891.5 1,021.9 1,165.6 1,517.2 a4.422> 1.64c 0.0000 
QQDC-A1B 1,086.6 260.2 0.240 368.1 929.5 1,072.6 1,226.2 1,594.3 b4.093> 1.64c 0.0000 
Runoff quartiles (mm)
Paired-sample Wilcoxon signed-rank test
WatershedsDataMean (mm)SD (mm)CVMinQ1MedianQ3Maxzcalzcrip-value
Wuxuan Baseline 633.4 117.3 0.185 367.6 559.4 645.4 711.5 902.8    
SDC-A1B 688.7 122.7 0.178 417.9 616.2 694.1 785.3 945.0 a4.772> 1.64c 0.0000 
QQDC-A1B 696.4 128.8 0.185 427.4 606.9 695.0 778.8 956.7 b2.057> 1.64c 0.0192 
Shijiao Baseline 1,015.7 263.5 0.259 385.8 845.1 959.5 1,113.9 1,620.5    
SDC-A1B 1,093.6 286.8 0.262 360.3 910.3 1,071.4 1,239.4 1,776.4 a4.463> 1.64c 0.0000 
QQDC-A1B 1,149.2 306.1 0.266 383.7 944.8 1,101.6 1,252.2 1,887.4 b4.648> 1.64c 0.0000 
Boluo Baseline 967.4 241.5 0.250 357.6 836.8 945.2 1,082.7 1,573.7    
SDC-A1B 1,029.4 241.4 0.235 375.9 891.5 1,021.9 1,165.6 1,517.2 a4.422> 1.64c 0.0000 
QQDC-A1B 1,086.6 260.2 0.240 368.1 929.5 1,072.6 1,226.2 1,594.3 b4.093> 1.64c 0.0000 

Zcal, Z-score of the calculated Wilcoxon statistics; Zcri, Z-score of the critical Wilcoxon statistics at a 5% significance level.

aPaired-sample Wilcoxon signed-rank test for comparing the baseline and SDC-A1B annual runoff time series.

bPaired-sample Wilcoxon signed-rank test for comparing the SDC-A1B and QQDC-A1B annual runoff time series.

cOne-tailed Z score of the critical Wilcoxon statistics at a 5% significance level; > SDC-A1B annual runoff is significantly greater than the baseline or the QQDC-A1B annual runoff is significantly greater than the SDC-A1B runoff.

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