根据西营河九条岭水文站1972—2019年逐年洪水水文要素摘录表,采用年最大值抽样法得到年最大日流量、春、夏季最大日流量共3个样本序列,用M-K检验法分析其变化趋势,并采用GEV分布对3组序列进行拟合分析,使用K-S法与PPCC检验法评价理论分布与实测序列的拟合精度。结果表明：GEV分布能够很好的拟合九条岭水文站的最大日流量序列。根据理论重现期分析,流域内春季发生洪水的次数在减少,夏季发生洪水的次数自1980s以来呈先减少后增加的趋势。山区径流受气候变化影响显著,增温变枯现象普遍。春季高频次的发生温度骤升现象,使得春季洪水发生时间提前,雪冰融水补给比例减少导致西营河流域春季发生洪水次数减少,夏季汛期降水量很大程度决定着流域内洪水大小,流域内年降水总量变化趋势与发生洪水事件的次数的年际变化趋势一致,均呈先升后降再升的波动趋势。

Scholars have paid close attention to the phenomenon of frequent flood events caused by climate change. Using the data from the annual flood hydrological elements extract table of Jiutiaoling hydrological station of the Xiying River from 1972 to 2019, we applied the annual maximum sampling method to obtained the annual maximum daily discharge and spring and summer maximum daily discharges. We calculated the respective basic moments of the three sample series and analyzed the trend change using the linear trend method. The M-K test method was used to test the trend of the series, the GEV distribution was used to analyze the trend, and the K-S method and PPCC test were used to evaluate the accuracy of fit of the theoretical distribution and the measured series. The results of the analysis revealed that from 1972 to 2019, there was a downward trend in the annual maximum daily discharge and the maximum daily discharge series in spring and summer, and the spring floods tended to occur earlier. The M-K test revealed that there was no significant change trend in the three sequ-ences. The GEV distribution can well fit the maximum daily discharge series of Jiutiaoling hydrological station. The annual maximum daily discharge series and spring maximum daily discharge series followed the Weibull distribution, and the summer maximum daily discharge series followed the Frechet distribution. The analysis of the theoretical return period showed that the number of floods in spring has been decreasing, whereas the number of floods in summer first decreased and then increased since the 1980s. The runoff in the mountainous area of the Xiying River Basin is affected significantly by climate change, and the phenomenon of increasing temperature and consequent drying up is common. The increase of precipitation cannot meet the supply of runoff and snow cover in the mountainous area, which causes a year by year decline of the runoff in the basin. The high frequency of sudden temperature rises in spring causes the spring flood to occur earlier, and the large temperature rise in winter hinders the formation of snow. The reduction of the proportion of ice and snow melt in the water supply reduces the frequency of spring floods in the Xiying River Basin. The precipitation in the summer flood season largely determines the size of floods in the basin, and the trend of variation of annual precipitation in the basin is closely related to the number of flood events. The change trend first increased, then decreased, and then increased.