Study On The Runoff Changes And Influencing Factors In The Water Conservation Area Of The Upper Reaches Of Yellow River Basin

As the main water-producing area of the entire Yellow River Basin,the water conservation area in the upper reaches of the Yellow River has continued to decline in recent decades,which has had an important impact on the water resources,water ecology and water security of the entire Yellow River Basin.It is an urgent need to study the characteristics and influencing factors of past runoff changes in the water conservation area of the upper reaches of the Yellow River,and to explore the runoff changes under the future climate model.In this paper,the variation characteristics of meteorological and hydrological data were analyzed by using the Mann-Kendall trend and mutation test method as the study area,and the"natural period"and"influence period"were divided according to the runoff sequence mutation test results.Based on the data of the natural period,the SWAT(Soil Water Assessment Tool)hydrological model of the study area was constructed,and the influence of climate change and human activities on the runoff changes in different regions during the study period was analyzed by simulating the quorum of the model,and the water consumption and storage capacity of large and medium-sized reservoirs in the study area from 2009 to2015 and the contribution of land use changes to runoff changes were further analyzed,so as to further analyze the contribution of human activities to runoff changes.The runoff changes under future climate scenarios are simulated and analyzed,and the laws and dynamic mechanisms of runoff changes in the upper reaches of the Yellow River Basin are explored at different spatio-temporal scales,with a view to providing decision-making basis and scientific guidance for the management of water resources,ecological environmental protection and high-quality development in the upper reaches of the Yellow River.The main conclusions of the study are as follows:(1)Using the natural runoff data of six hydrological stations in the study area from 1965 to 1985,the SWAT model was determined and verified at the annual,month and daily scales.The results show that the periodic R~2 and Ens on the annual scale are both greater than 0.80,and the verification period R~2 and Ens are greater than 0.70;the periodic R~2 and Ens are both greater than 0.84 on the monthly scale,and the R~2 and Ens in the verification period are both greater than 0.77;and the periodic and verification period R~2 and Ens on the daily scale are greater than 0.70.The relative errors of the six sites on the three time scales were between±15%during the rate periodicity and the validation period.In general,the SWAT model has good applicability in the water conservation area of the upper reaches of the Yellow River.(2)The actual measured runoff sequence in the study area from 1965 to 2015was tested for mutation testing,and combined with the construction time of the reservoir,1986 was divided into mutation points of runoff sequence in the study area,and the natural period(1965-1985)and the impact period(1986-2015)were divided according to the mutation points.The trend analysis of hydrometeorological data in the study area shows that the precipitation and temperature in the study area show a significant upward trend from 1965 to 2020.The overall runoff in the study area showed a downward trend from 1965 to 2015.(3)Compared with the base period of 1965-1985,climate change was the leading factor in the reduction of runoff in the source area from 1986 to 2015,with a contribution rate of about 81.46%.Human activities are the leading drivers of the reduction of runoff in the downstream agricultural areas of the source area from 1986to 2015,with a contribution rate of about 78.95%,of which human activities are mainly manifested as industrial and agricultural water consumption and reservoir capacity regulation,accounting for about 77.00%of the contribution of all human activities.The contribution of land-use change to the impact of runoff change is relatively small in all human activity contributions.(4)Under the scenario path of SSP126,SSP245 and SSP585 of the CNRM-CM6-1 climate model,the precipitation in the study area from 2021 to 2100increased by about 10.82%-23.35%compared with the historical period(1986-2020),and the temperature increased by about 1.9°C-3.9°C compared with the historical period.While maintaining the current land use scenario unchanged,the runoff under the SSP126 scenario increased by 16.92%compared with the historical period(1986-2020),increased by 16.58%under the SSP245 scenario path,and increased by33.32%under the SSP585 scenario path.