| The response mechanism of water resources in a watershed under changing environment has become a hot and frontier issue in the current global change research,especially the watershed in the alpine and cold regions such as the source of Yangtze River is more sensitive to the change of climate factors.Climate change will have a profound impact on the runoff evolution law and water circulation mechanism of the watershed,and then bring new challenges to the spatial and temporal allocation of water resources and the development and utilization of water resources.Therefore,the characteristics and laws of climate change factors and water resources evolution are studied,and the impacts of climate change on runoff and its components are evaluated qualitatively and quantitatively,It is of great significance to the sustainable utilization of water resources and the maintenance of ecological functions of the source area of Yangtze River.Based on the precipitation,temperature and evapotranspiration data of the source region of Yangtze River from 1966 to 2015,and the runoff data of Zhimenda hydrological station from 1966 to 2015,this paper uses the digital filtering method,linear analysis,man Kendall rank correlation test,Spearman rank test,sliding t test,ordered clustering method and Morlet wavelet theory in the comprehensive analysis Based on the analysis of the variation characteristics of climate factors,runoff and its components in the source region of the Yangtze River in recent 50 years,the response process of runoff to climate change was deeply studied,and the driving factors of runoff and its components in the source region of the Yangtze River were qualitatively and quantitatively analyzed by combining partial correlation analysis,Granger causality test,cumulant slope method and double cumulative curve.The main achievements are as follows:(1)In the source region of Yangtze River in recent 50 years,the precipitation showed a significant upward trend and mutation occurred in 2004,with a period of 28 a and 19-20a;the temperature showed a significant upward trend and mutation occurred in 2002,with a period of 28 a and 16-17a;the evapotranspiration showed a significant upward trend and mutation occurred in 1995,with a period of 28 a and 18-19a;the evapotranspiration,precipitation and temperature showed a period of 28 a The maximum energy period and the significant period of evapotranspiration from 18 to 19 years are caused by the combined effect of precipitation from 19 to 20 years and temperature from 16 to 17 years.(2)From 1966 to 2015,the annual average runoff depth in the source area of the Yangtze River is 90.72 mm,the interannual fluctuation of the annual runoff depth is relatively gentle in its decadal fluctuation,the annual distribution of the runoff depth is uneven,and the process curve is "single peak type",and the peak value appears in July,with a value of20.37 mm.The digital filtering method is used to segment the base flow of the runoff in the source area of the Yangtze River.The average annual surface runoff depth is 41.72 mm,and the base flow depth is 48.99 mm.The peak value of the monthly runoff depth curve of the surface runoff depth appears in July,and the peak value of the monthly runoff depth curve of the base flow depth appears in August,and its distribution is relatively stable.Runoff depth and its components showed an increasing trend,and had a mutation in 2004,which was consistent with the year of precipitation mutation.The runoff fluctuation cycle and precipitation fluctuation cycle have a common cycle of about 3 years and 7 years,and a similar cycle of about 16 years with temperature and evapotranspiration.After the mutation year of 2004,the BFI index of the source area decreased,indicating that there is more surface runoff supply after the mutation.(3)Partial correlation analysis showed that there was a significant positive correlation between precipitation and runoff and its components,and also between temperature and runoff and its components under the condition of controlling the other two climate factors.However,there was a false correlation between evapotranspiration and runoff and its components.(4)Granger causality test shows that in the past 50 years,precipitation is the Granger causality of runoff depth and base flow depth,and temperature is the Granger causality of runoff depth and its components.Compared with the base period(1966-2003),climate factors,runoff and its components did not constitute the Granger causality,and the precipitation sequence in the change period(2004-2015)was the Granger causality.Comprehensive correlation analysis and Granger causality test show that precipitation is the main reason to control the change of runoff and its components in the source area,while the influence of temperature can not be ignored.Considering the influence of continuous warming is more helpful to predict the change of river runoff composition under the background of climate change.(5)Due to the direct influence of precipitation,evapotranspiration and the indirect influence of temperature and other factors,the runoff depth and its components in the source region of the Yangtze River show an increasing trend in recent 50 years.The contribution rate of precipitation to the runoff and its components is about 54%-63%,that of temperature to the runoff and its components is about 0%-14%,and evapotranspiration is about 32%-37%. |
