| Under the combined effect of climate change and human activities, spatial and temporal distributions of runoff have been significantly changed.Understanding the variation characteristics of runoff and its influencing factors are better able to the development and utilization of water resources, and provide theoretical guidance for the regional development. Based on the runoff data measured by four hydrological stations in the upper reaches of Fenhe River from 1956 to 2000, combined with precipitation and annual average temperature and other meteorological factors, linear regression, accumulation anomaly, Five point three sliding curve, the Mann-Kendall, orderly clustering, Empirical Mode Decomposition were used to analyze the variation characteristics of runoff and meteorological factors. Double mass curve, cross wavelet transform, wavelet coherence and statistical methods were used to estimate quantitatively the influence of human activities on the runoff, study sunspot activity, ENSO cycle affecting the changes in the runoff. The main content and results of this study are as follows:(1) The intra-annual distribution of runoff of four hydrological stations in the upper reaches of Fenhe River was extremely uneven. The largest runoff was in August, and the least runoff was in January. In the runoff distribution of four seasons, the proportion of summer and autumn are larger than spring and winter.Annual distribution curve of four hydrological stations showed a twin peaks distribution.(2) Apparent periodicities(high-low) of runoff of Fenhe reservoir hydrological station, Zhaishang hydrological station and Lancun hydrological station can be observed.Apparent periodicities(high-low-high-low) of runoff of Shangjingyou hydrological station can be observed. The annual runoff of Shangjingyou hydrological station varies abruptly in 1967. The annual runoff of Fenhe reservoir hydrological station and Lancun hydrological station varies abruptly in 1969. The annual runoff of Zhaishang hydrological station varies abruptly in 1970, later than above two hydrological stations. There were obvious periodic variations with scales 2~4a, 10 a for the annual runoff series in the upper reaches of Fenhe River.And in 45 years, there had been abrupt reductions in the observed annual runoff.(3) The average annual rainfall is 490.50 mm in the upper reaches of Fenhe River from 1956 to 2000. There had been reductions in the observed annual precipitation. The annual precipitation varies abruptly in 1967. There were obvious periodic variations with scales 2~3a, 10 a for the annual precipitation series. Average annual temperature of 45 years is 9.77 ℃ in the upper reachesof Fenhe River. There had been abrupt additions in the observed annual temperature.The annual temperature varies abruptly in 1993. There were obvious periodic variations with scales 2~4a, 8a or 16 a for the annual temperature series. The average annual evaporation is 1735.29 mm in the upper reaches of Fenhe River from 1956 to 2000. There had been abruptly reductions in the observed annual evaporation. The annual evaporation varies abruptly in1974. There were obvious periodic variations with scales 2~4a, 14 a for the annual precipitation series.(4)Through correlation analysis,path analysis and Set Pair Analysis,analysis results showed that runoff is closely related to the annual rainfall of four hydrological stations in the upper reaches of Fenhe River,and both showed a significant positive correlation.The annual average temperature was weakly related to the runoff,and both showed a negative correlation.In addition, there were other factors driving the evolution of runoff in the upper reaches of Fenhe River.Before mutation year and after mutation year,rainfall was closely related to the annual runoff of Shangjingyou hydrological station and Fenhe reservoir hydrological station.Before mutation year,rainfall was closely related to the annual runoff of Zhaishang hydrological station and Lancun hydrological station.after mutation year,the human activities had become the main factor that causes the runoff decrease compared with annual rainfall.(5)Contrast curve of runoff of four hydrological stations in the upper reaches of Fenhe River and sunspot were similar, in the peak years of sunspot,runoff reduced; in the valley years of sunspot, runoff increased.And sunspot activity was significantly correlated to annual runoff amount.There was significant in-phase resonance oscillation between runoff and sunspot number in8~11a, variation of runoff was earlier than the change of sunspot activity.(6)The cross wavelet figure of runoff of four hydrological stations in the upper reaches of Fenhe River and MEI was similar.There was significant in-phase resonance oscillation between runoff and MEI in 1~4a,variation of MEI was earlier than the change of runoff.From wavelet coherence spectrum analysis,both showed significant in-phase resonance oscillation in 3~4a,and observed a negative correlation.When El Nino occurred, the runoff decreased; in the end year of El Nino the runoff increased.When La Nina occurred, the runoff increased; in the end year of La Nina the runoff decreased.(7)The runoff in the upper reaches of Fenhe River with normalized difference vegetation index showed a significant positive correlation.Normalized difference vegetation index has a certain degree of influence on runoff change. |
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