Abstract:

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.

Key words: generalized extreme value distribution, flood frequency, temperature soared, climate change, Xiying River Basin, Northwest China