Research On Multi-model Attribution Of Runoff Changes In The Upper Reach Of The Heihe River Basin

The upper reaches of Heihe River,located in the arid area of Northwest China,is the main runoff producing area of Heihe River Basin.Its runoff evolution has a significant impact on the whole basin.Since the 1990 s,the temperature in Qilian Mountains has risen obviously,and the hydrological cycle has been intensified.Add the influence of other factors,the spatiotemporal evolution of the hydrological cycle in Heihe River Basin has become more and more complicated.Scholars at home and abroad have analyzed the attribution of runoff changes in many river basins,including Heihe River Basin.Among these methods,statistical method,empirical semi-empirical formula method and hydrological model method are commonly used.Based on the runoff climate data of the upper reaches of Heihe River from 1960 to 2015,and on the basis of analyzing the trend and catastrophe characteristics of runoff variation in the study area by using various statistical methods,this study chooses three methods(double mass curve method,Budyko hypothesis empirical formula method and SWAT model)for quantitative study.Those methods represent general statistical model,empirical formula-based Hydrothermal Coupling equilibrium model and physical mechanism-based distributed hydrological model,respectively.Combined with the climate conditions and land use types in the basin,this paper explores the attribution of runoff change in the upper reaches of Heihe River,and quantitatively analyses the contribution rate of different factors to runoff change in the upper reaches of Heihe River.The main conclusions are as follows:(1)During the study period(1960-2015)there was a significant increase in the runoff sequence in the upper reaches of the Heihe River,and abrupt changes occurred in 1997 and 2004.Based on this,the baseline period(1960-1997)and the mutation period I(1998-2004),Three stages of mutation period II(2005-2015).(2)From 1960 to 2015,the trend of changes in the average annual temperature,annual precipitation and other climatic factors in the upper reaches of the Heihe River,as well as the time of mutation points,and the characteristics of runoff changes showed a high consistency.Permanent glaciers and snowfields appeared after the mid-1990 s.The area reduction coincides with the 1997 abrupt change point of runoff.The underlying surface conditions in the region are relatively stable,and the upstream human activities are weak,which has little impact on runoff changes.Under the multi-model attribution analysis,the increase in precipitation and changes in underlying surface conditions have a positive effect on the increase in runoff,and the increase in temperature has a negative effect on the increase in runoff;the coupling effect of precipitation-temperature-land use type changes and other factors have caused the increase in runoff a positive effect.(3)The results of multi-model attribution make up the limitation of single method,and it is considered that the contribution rate of climate change is decreasing in two mutation period,and precipitation change is the dominant factor of runoff change.The contribution rate of precipitation change is about 120% and 80% ? 100% in mutation period I and mutation period II,and the result of double mass curve method in mutation period I is 80%,lower than others;Budyko hypothesis empirical formula method and SWAT model suppose that the contribution rate of temperature change decreases from-40% ?-70% in mutation period I to-20% ?-30% in mutation period II;On the basis of the above,the coupling factors of land use and precipitationair temperature-land use were separated by SWAT model.The contribution rate of cover type change was less than 10%,and the coupling contribution rate increased from 7% in mutation period I to 16% in mutation period II,the interaction between the factors is increasing;and the contribution rate of other factors to the change of runoff is about 30% ? 40%.