Baseflow Change Of Different Geomorphologic Regions In The Middle Yellow River And Its Responses To Ecological Construction

Under the influence of climate change and large-scale human activities,the hydrological process in middle reaches of the Yellow River is strongly disturbed,so as to base flow.Therefore,quantitative analysis of the impacts of climate change and human activities on baseflow has great meanings to ecological en vironment construction and sustainable utilization of water resources in middle reaches of the Yellow River.Firstly,the study compared applicability of different baseflow segmentation methods in middle reaches of the Yellovw River,and selected DF4 of digital filtering method to segment baseflow of three typical watersheds(Huangfuchuan watershed,Hailiutu watershed and Dalihe watershed)which represent different geomorphic types.Secondly,M-K analysis was used to test baseflow changing trend in different periods,and complex Morlet wavelet analysis was used to judge baseflow periodicity.At the same time,double cumulative curve method was selected to identify the change point of baseflow and to verify it by cumulative anomaly method and ordered clustering method.Then,changing characteristics of baseflow before and after the change points were compared.Finally,relationship between precipitation,ecological construction measures and baseflow was indicat.ed by cross-wavelet analysis,and the contribution of climate change and human activities to baseflow was calculated by slope change ratio of cumulative quantity method.The main conclusions are as follows:(1)The baseflow of typical watersheds in different geomorphic areas shows a downward trend and periodic characteristics.The baseflow in Huangfuchuan,Hailiutu and Dalihe watershed was calculated by 9 segment methods.The baseflow index was analyzed by eigenvalue statistics and correlation analysis.The results show that DF4 in digital filtering method was the best one for baseflow segmentation.The annual baseflow of Huangfuchuan,Hailiutu and Dalihe watershed was 0.15,0.61 and 0.69 billion m3 respectively.The annual,decreasing trend(p<0.01).Due to located in different geomorphological regions,the baseflow index of Huangfuchuan,Hailiutu and Dalihe watershed were quite different.Annual baseflow indices were 0.12,0.79 and 0.55,respectively.The baseflow index of Huangfuchuan watershed showed a significant downward trend(p<0.001),while the others no significant.Complex Morlet wavelet analysis showed that there was a complete primary period of annual baseflow in Hailiutu and Dalihe watershed,which occurred at the time scale of 42 and 38 year,respectively,while Huangfuchuan River Basin does not have a complete evolution law.(2)The change point of baseflow in three watersheds were identified and differences before and after change point were compared.The change point of annual baseflow in Huangfuchuan watershed was 1982,Hailiutu watershed were 1967 and 1986,Dalihe watershed were 1971 and 1996.These change points were verified by cumulative anomaly method and ordered clustering method.The change rate of annual baseflow in Huangfuchuan watershed before and after change point is 75.78%,he change rates of annual base flow of Hailiutu watershed before and after two change point years were between 20%and 45%,and,the change rate of Dalihe watershed was less than 30%.Before and after the change point,the change rate of base flow of flood season in Huangfuchuan watershed was 71.54%,in Hailiutu watershed was 47.03%,in Dalihe watershed was 27.02%;the change rate of base flow in non-flood season in Huangfuchuan watershed was 88.79%,in Hailiutu watershed was 34.06%,and in Dalihe watershed was 14.69%.The change rate of precipitation in Dalihe watershed is more than 45%after the change point,while that in other watersheds weres less than 15%.(3)Ecological construction impact on watershed base flow was stronger than climate change.Cross wavelet analysis result showed that,precipitation,NDVI,and base flow of three watersheds have good linear regression relationship,multiple resonant periodic were found between terrace cumulation area in Huangfuchuan Watershed and annual base flow amount,with large phase change.Contribution rate of flood season precipitation to base flow was 1.95%,10.26%,and 42.99%for Huangfuchuan,Hailiutu and Dalihe watershed,respectively,human activity contributions were 98.05%,89.74%,57.01%,respectively;in non-flood season,precipitation contributions were 52.50%,16.82%,46.51%,while human activity contributions were 47.50%,83.18%,53.49%.(4)The relationship between base flow and check dam in different periods were discussed.Large scale check dam cumulative capacity change point was 1989 in Huangfuchuan watershed,1971 in Dalihe watershed.Before the change point,large scale check dam cumulative capacity had no significant relationship with annual,flood season and non-flood season hydrology parameter in Huangfuchuan watershed;large scale check dam cumulative capacity had no significant relationship with annual base flow and annual base flow parameter in Dalihe Watershed.After the change point,large scale check dam cumulative capacity had significant negative relationship with annual base flow rate,annual base flow parameter(p<0.05)and flood season base flow rate(p<0.01)in Huangfuchuan watershed;large scale check dam cumulative capacity had significant negative relationship with annual base flow rate(p<0.05),while no significant relationship with flood season and non-flood season base flow rate.Base flow rate decreases were mainly induced by coal mine in Huangfuchuan watershed while check dam construction in Huangfuchuan watershed.As the human activity like coal mine and dam construction increase,the base flow rate in middle reach of Yellow River will continuously decrease.