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Although the trends and abrupt changes in peak flows at the four stations were non-significant, the stationarity characteristics should be further examined. We used the Augmented Dickey–Fuller (ADF) unit root test to analyze the stationarities of peak flow series for the four stations. The ADF method is a classic method which can examine the stationarity of a time series (Zhao & Chen 2015). Table 3 lists the P value statistics from ADF. Note that the P value statistics in the Fenshi, Pingshi and Lishi series are greater than the critical value 0.05, implying the nonstationary nature of peak flows at these stations. On the contrary, the P value statistic in the Shijiao series is smaller than 0.05, indicating the stationarity of the series. As the Feilaixia reservoir operation may alter, changing the properties of peak flows in the Shijiao station, we omitted the records after 1998, when the Feilaixia reservoir was constructed, and reanalyzed the stationarity of the new series. Results show, as expected, a nonstationary characteristic of the peak flow series covering 1954–1997 at the Shijiao station (Table 3). These results on the one hand can explain the nonstationarity of peak flows in BRB, and on the other hand infer a possible influence of the Feilaixia reservoir operation on the changing property of peak flows at the Shijiao station.

Table 3

ADF test results of the peak flow series for the four stations in BRB

StationDickey–FullerLag orderP value
Fenshi −3.03 0.17 
Pingshi −3.08 0.15 
Lishi −3.15 0.11 
Shijiao (during 1954–2007) −3.74 0.03 
Shijiao (during 1954–1997) −3.46 0.06 
StationDickey–FullerLag orderP value
Fenshi −3.03 0.17 
Pingshi −3.08 0.15 
Lishi −3.15 0.11 
Shijiao (during 1954–2007) −3.74 0.03 
Shijiao (during 1954–1997) −3.46 0.06 

P ≤ 0.05 and P> 0.05 indicate the series are stationary and nonstationary, respectively.

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