Analysis Of Runoff Variation And Its Attribution In The Upper Reaches Of Weihe River

Under the influence of global climate change and human activities,runoff has changed dramatically,which also directly affects the development,allocation,management and utilization of water resources.The driving factors of quantitative analysis runoff are beneficial to the scientific and rational management of water resources.Therefore,based on the data of runoff,precipitation,air temperature,potential evapotranspiration and land use from 1960 to 2018 in the upper reaches of the Wei River Basin,this paper analyzed the characteristics of runoff change and its influencing factors,and discussed the correlation between runoff change and influencing factors,and the quantitative attribution analysis was carried out.The main conclusions were as follows:(1)The annual distribution of runoff presents a“Double peak”,and the interannual variation shows a significant decreasing trend.The annual mean runoff and the seasonal mean runoff decreased significantly(P<0.01),and the abrupt change point of the former was 1985,the mutation years of each season were 1978,1984,1990 and 1985,and all of them were super abundant years.The Hurst Indices of annual runoff,spring annual runoff,summer annual runoff,autumn annual runoff and winter annual runoff were0.37,0.39,0.43,0.36 and 0.25,respectively,the anti-persistence of annual runoff in winter is the strongest.The annual runoff decreased significantly in the wet season and the dry season(P<0.01),which had abrupt changes in 1989 and 1980,respectively,in the dry season,the annual runoff showed a weak persistence(H=0.52).(2)In the meteorological elements,the air temperature and potential evapotranspiration showed a significant upward trend except for the precipitation which showed a non-significant downward trend.The mean annual precipitation showed no significant decreasing trend(P=0.44),and the future change of surface precipitation showed anti-persistence(H=0.28).There were the first and second main cycles in 19 and 20 years The annual mean temperature showed a significant increasing trend(Z=5.587,P<0.01),and the surface mean temperature showed a reverse persistence(H=0.38).The mutation occurred in 1997 and 1998,there were the first and second main periods of 30 and 15 years,and the annual potential evapotranspiration was significantly increased(Z=2.079,P<0.05).The R/S analysis indicated that the potential evapotranspiration in the Upper Wei River was anti-persistent(H=0.27)with the first and second main cycles of 13 and 12 years.(3)From 1980 to 2020,cultivated land and grassland were the main types of land use.The area of cultivated land,water area and unused land decreased,while the area of woodland,grassland and construction land increased.Compared with 1980,the area of cultivated land in the watershed decreased by 1.88%,the area of forest increased by 0.69%,the area of grassland increased by 0.47%and the area of water decreased by 0.02%,the proportion of construction land increased by 0.77%and the proportion of unused land decreased by 0.01%.Among them,the construction land increased 264.1 km~2,the cultivated land decreased 651.12 km~2,the forest land increased 236.39 km~2 and the grassland increased 160.87 km~2.The NDVI increased significantly at a rate of 9.1%/(10 a)(P<0.01),and the coefficient of variation was about 0.10.(4)The main driving factor of runoff change in the upper reaches of the Wei River River is human activities,accounting for 52.95%.Based on the water-heat coupling equation of Budyko hypothesis,the contribution of precipitation and potential evapotranspiration to the change of runoff is 19.96%and 27.09%,and the contribution of human activities to the change of runoff is 52.95%.The elastic coefficient of the underlying surface parameter is between 0.3 and 3.4,and its absolute value has an increasing trend,indicating that the influence of human activities has a gradually strengthening trend.