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To test the differences in QQDC-A1B and SDC-A1B monthly precipitation data sets of Boluo watershed, the paired-sample Wilcoxon signed-rank test was conducted, which compares two dependent and non-normal samples and assesses whether their population mean ranks differ significantly. Table 3 shows that in summer and early autumn (June–September), the QQDC-A1B precipitation is significantly higher than SDC-A1B at a 5% significance level, whereas the spring (March–April) precipitation of QQDC-A1B is significantly lower than that of SDC-A1B at the same significance level. The other two watersheds also have a similar trend (not shown in this paper).

Table 3

Statistical properties of QQDC-A1B and SDC-A1B monthly precipitation in Boluo watershed

Precipitation quartiles (mm)
Paired-sample Wilcoxon signed-rank test
MonthDataMinQ1MedianQ3MaxZcalZcrip-value
January QQDC-A1B 0.3 9.3 21.3 56.5 152.7 4.152 > 1.64b 0.0000 
 SDC-A1B 0.4 8.7 20.8 53.8 150.0    
February QQDC-A1B 5.4 23.2 38.9 74.6 295.6 0.267 = 1.96a 0.3960 
 SDC-A1B 7.5 25.4 40.8 71.3 251.8    
March QQDC-A1B 7.7 78.4 117.2 195.5 550.9 −3.270 < 1.64b 0.0003 
 SDC-A1B 11.0 86.7 133.9 195.3 521.2    
April QQDC-A1B 33.6 128.3 189.0 252.5 516.9 −2.980 < 1.64b 0.0010 
 SDC-A1B 36.1 135.6 197.7 253.2 426.3    
May QQDC-A1B 49.7 280.4 343.3 471.9 651.5 −1.460 = 1.96a 0.1456 
 SDC-A1B 45.1 275.9 348.0 462.3 672.2    
June QQDC-A1B 89.9 239.3 306.6 402.9 799.3 3.414 > 1.64b 0.0002 
 SDC-A1B 93.0 238.7 295.1 396.8 778.3    
July QQDC-A1B 88.3 159.0 217.8 335.3 496.3 3.332 > 1.64b 0.0002 
 SDC-A1B 89.1 157.1 215.1 276.7 487.2    
August QQDC-A1B 97.9 150.9 218.2 303.7 457.5 2.818 > 1.64b 0.0019 
 SDC-A1B 101.5 148.1 220.1 283.8 383.7    
September QQDC-A1B 60.4 97.2 154.0 202.9 478.7 1.820 > 1.64b 0.0337 
 SDC-A1B 55.4 93.1 153.2 204.7 478.7    
October QQDC-A1B 0.0 20.9 56.2 104.7 481.0 −0.926 = 1.96a 0.8254 
 SDC-A1B 0.2 38.6 69.1 108.4 299.5    
November QQDC-A1B 0.1 5.6 29.5 49.7 83.1 4.772 > 1.64b 0.0000 
 SDC-A1B 0.1 3.0 17.6 30.9 64.2    
December QQDC-A1B 0.1 2.1 7.0 38.1 333.6 −3.25 < 1.64b 0.0003 
 SDC-A1B 0.5 6.8 15.8 55.9 194.8    
Precipitation quartiles (mm)
Paired-sample Wilcoxon signed-rank test
MonthDataMinQ1MedianQ3MaxZcalZcrip-value
January QQDC-A1B 0.3 9.3 21.3 56.5 152.7 4.152 > 1.64b 0.0000 
 SDC-A1B 0.4 8.7 20.8 53.8 150.0    
February QQDC-A1B 5.4 23.2 38.9 74.6 295.6 0.267 = 1.96a 0.3960 
 SDC-A1B 7.5 25.4 40.8 71.3 251.8    
March QQDC-A1B 7.7 78.4 117.2 195.5 550.9 −3.270 < 1.64b 0.0003 
 SDC-A1B 11.0 86.7 133.9 195.3 521.2    
April QQDC-A1B 33.6 128.3 189.0 252.5 516.9 −2.980 < 1.64b 0.0010 
 SDC-A1B 36.1 135.6 197.7 253.2 426.3    
May QQDC-A1B 49.7 280.4 343.3 471.9 651.5 −1.460 = 1.96a 0.1456 
 SDC-A1B 45.1 275.9 348.0 462.3 672.2    
June QQDC-A1B 89.9 239.3 306.6 402.9 799.3 3.414 > 1.64b 0.0002 
 SDC-A1B 93.0 238.7 295.1 396.8 778.3    
July QQDC-A1B 88.3 159.0 217.8 335.3 496.3 3.332 > 1.64b 0.0002 
 SDC-A1B 89.1 157.1 215.1 276.7 487.2    
August QQDC-A1B 97.9 150.9 218.2 303.7 457.5 2.818 > 1.64b 0.0019 
 SDC-A1B 101.5 148.1 220.1 283.8 383.7    
September QQDC-A1B 60.4 97.2 154.0 202.9 478.7 1.820 > 1.64b 0.0337 
 SDC-A1B 55.4 93.1 153.2 204.7 478.7    
October QQDC-A1B 0.0 20.9 56.2 104.7 481.0 −0.926 = 1.96a 0.8254 
 SDC-A1B 0.2 38.6 69.1 108.4 299.5    
November QQDC-A1B 0.1 5.6 29.5 49.7 83.1 4.772 > 1.64b 0.0000 
 SDC-A1B 0.1 3.0 17.6 30.9 64.2    
December QQDC-A1B 0.1 2.1 7.0 38.1 333.6 −3.25 < 1.64b 0.0003 
 SDC-A1B 0.5 6.8 15.8 55.9 194.8    

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

aTwo-tailed Z score of the critical Wilcoxon statistics at a 5% significance level.

bOne-tailed Z score of the critical Wilcoxon statistics at a 5% significance level; > QQDC-A1B monthly precipitation is significantly greater than the SDC-A1B data; = QQDC-A1B and SDC-A1B monthly precipitation data sets are not significantly different; < QQDC-A1B monthly precipitation is significantly less than the SDC-A1B data.

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