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Table 4 shows that the SDC-A1B mean annual precipitation undergoes an increase of 4.4% in Wuxuan, 6.1% in Shijiao, and 4.6% in Boluo; the QQDC-A1B mean annual precipitation has a slightly larger increase rate (6.8%, 9.6%, and 7.5% in Wuxuan, Shijiao, and Boluo, respectively). These upward trends in annual precipitation basically agree with the study of Liu et al. (2009), who projected an obvious increase in annual precipitation from 2011 to 2060 using GCM ECHAM5/MPI-OM. The paired-sample Wilcoxon signed-rank test (Table 4) confirms that future annual precipitation time series are greater than the baseline at a 5% significance level, and the QQDC method yields a significantly higher annual precipitation than the SDC algorithm at the same significance level. With respect to the variability of annual precipitation, the standard deviations of SDC-A1B and QQDC-A1B are, respectively, 2.7–10.7% and 8.8–17.9% higher than the baseline, indicating a mild increase in fluctuation magnitudes of future annual precipitation. Considering the increased annual mean precipitation, the CVs of the two future data sets do not change evidently, compared with the baseline CV. Moreover, the first quartile (Q1), median, the third quartile (Q3), and maxima of the annual precipitation time series in both A1B scenarios of all three watersheds are consistently larger than the baseline, in particular with significantly higher values in QQDC-A1B (Table 4). This finding implies that more wet years would likely occur in the future, especially in the QQDC-A1B scenario.

Table 4

Statistical properties of annual precipitation under the baseline, QQDC-A1B, and SDC-A1B scenarios

Precipitation quartiles (mm)
Paired-sample Wilcoxon signed-rank test
WatershedsDataMean (mm)SD (mm)CVMinQ1MedianQ3MaxZcalZcrip-value
Wuxuan Baseline 1,344.5 138.2 0.103 1,019.1 1,257.9 1,366.2 1,438.8 1,602.1    
 SDC-A1B 1,404.8 142.5 0.101 1,088.0 1,312.4 1,427.0 1,499.2 1,659.5 a4.772> 1.64c 0.0000 
 QQDC-A1B 1,435.4 150.3 0.105 1,128.2 1,320.8 1,464.2 1,534.4 1,717.9 b4.669> 1.64c 0.0000 
Shijiao Baseline 1,666.4 272.1 0.163 1,088.5 1,508.0 1,628.5 1,754.1 2,310.9    
 SDC-A1B 1,768.3 301.3 0.170 1,048.3 1,588.5 1,718.7 1,914.3 2,501.2 a4.566> 1.64c 0.0000 
 QQDC-A1B 1,826.7 320.8 0.176 1,076.9 1,619.5 1,772.4 1,924.3 2,622.1 b4.566> 1.64c 0.0000 
Boluo Baseline 1,792.8 307.8 0.172 924.8 1,608.9 1,761.5 1,901.2 2,433.3    
 SDC-A1B 1,876.3 319.8 0.170 932.1 1,699.6 1,842.8 2,000.2 2,541.4 a4.648> 1.64c 0.0000 
 QQDC-A1B 1,927.3 339.4 0.176 910.1 1,704.3 1,934.5 2,129.6 2,591.0 b3.743> 1.64c 0.0000 
Precipitation quartiles (mm)
Paired-sample Wilcoxon signed-rank test
WatershedsDataMean (mm)SD (mm)CVMinQ1MedianQ3MaxZcalZcrip-value
Wuxuan Baseline 1,344.5 138.2 0.103 1,019.1 1,257.9 1,366.2 1,438.8 1,602.1    
 SDC-A1B 1,404.8 142.5 0.101 1,088.0 1,312.4 1,427.0 1,499.2 1,659.5 a4.772> 1.64c 0.0000 
 QQDC-A1B 1,435.4 150.3 0.105 1,128.2 1,320.8 1,464.2 1,534.4 1,717.9 b4.669> 1.64c 0.0000 
Shijiao Baseline 1,666.4 272.1 0.163 1,088.5 1,508.0 1,628.5 1,754.1 2,310.9    
 SDC-A1B 1,768.3 301.3 0.170 1,048.3 1,588.5 1,718.7 1,914.3 2,501.2 a4.566> 1.64c 0.0000 
 QQDC-A1B 1,826.7 320.8 0.176 1,076.9 1,619.5 1,772.4 1,924.3 2,622.1 b4.566> 1.64c 0.0000 
Boluo Baseline 1,792.8 307.8 0.172 924.8 1,608.9 1,761.5 1,901.2 2,433.3    
 SDC-A1B 1,876.3 319.8 0.170 932.1 1,699.6 1,842.8 2,000.2 2,541.4 a4.648> 1.64c 0.0000 
 QQDC-A1B 1,927.3 339.4 0.176 910.1 1,704.3 1,934.5 2,129.6 2,591.0 b3.743> 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 precipitation time series.

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

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

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