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Using linear regressions, trends of the annual peak flows of the four hydrological stations in BRB were analyzed (Figure 2), and the statistical eigenvalues of the four series were calculated (Table 2). As seen in Figure 2, the annual peak flows exhibited large interannual fluctuations and upward trends. The growth rates of the series of Fenshi, Pingshi, Lishi and Shijiao stations are 4.77, 15.46, 19.09 and 27.42 m3/s·a, respectively. The maximum, minimum and mean values of peak flows in Table 2 indicate that the annual peak flows tended to increase from the Fenshi to the Shijiao station. The P values of the series are respectively 0.375, 0.098, 0.105 and 0.324 (Table 2), all of which are greater than 0.05. In other words, none of the upward trends are statistically significant. The maximum eigenvalues of the time series at the Fenshi, Pingshi, Lishi and Shijiao stations are 1,990, 4,830, 8,800 and 17,400 m3/s, respectively. With the exception of the maximum at the Fenshi station that occurred in 1994, all the stations' maxima occurred in 2006. Furthermore, the maxima of the series increased from the Fenshi to the Shijiao station. The coefficients of deviation (Cv) of the four series, on the other hand, decrease in value from the Fenshi to the Shijiao station. This signifies that the annual peak flow series of the Fenshi station was more discrete, though with a lower magnitude, compared with the other three stations.
Table 2

Statistical eigenvalues of the annual peak flows at the four stations in BRB

StationFenshiPingshiLishiShijiao
Maximum (m3/s) 1,990 4,830 8,800 17,400 
Minimum (m3/s) 184 636 630 2,740 
Mean (m3/s) 629 1,591 2,538 9,876 
P value 0.375 0.098 0.105 0.324 
Coefficient of deviation (Cv0.569 0.495 0.521 0.319 
Coefficient of skew (Cs1.810 1.992 2.402 0.234 
StationFenshiPingshiLishiShijiao
Maximum (m3/s) 1,990 4,830 8,800 17,400 
Minimum (m3/s) 184 636 630 2,740 
Mean (m3/s) 629 1,591 2,538 9,876 
P value 0.375 0.098 0.105 0.324 
Coefficient of deviation (Cv0.569 0.495 0.521 0.319 
Coefficient of skew (Cs1.810 1.992 2.402 0.234 

P ≤ 0.05 denotes the trend in the series is beyond the 0.05 significance level.

Figure 2

Inter-annual changes in annual peak flows at the (a) Fenshi, (b) Pingshi, (c) Lishi and (d) Shijiao stations. The dashed straight lines with linear equations denote linear trends of the annual peak flows.

Figure 2

Inter-annual changes in annual peak flows at the (a) Fenshi, (b) Pingshi, (c) Lishi and (d) Shijiao stations. The dashed straight lines with linear equations denote linear trends of the annual peak flows.

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