Spatial Evolution Of Water Yield And Runoff Scale Effect In The Jinghe River Basin

The Jinghe River Basin belongs to the Loess Plateau,with ravines vertical and horizontal,and serious soil erosion.However,there is still a big gap in the existing research results on the spatial changes and spatial scale effects of the hydrological parameters of the basin.Therefore,in this article,the SWAT model is mainly used for research,combined with empirical orthogonal function(EOF),geographic detectors,and regression analysis,to reveal the characteristics of the hydrological parameters in the Jinghe River Basin in space,and analyze the driving factors of the hydrological parameters.The multi-spatial scale effect of runoff in this watershed is clarified.the main conclusions were as follows:(1)Based on the runoff observation data of three hydrological stations(Qingyang,Yangjiaping,Zhangjiashan)in the Jing River Basin,the Soil and Water Assessment Tool(SWAT)is used to conduct the sequential single-site calibration(SSSC)and the simultaneous multi-site calibration(SMSC).The two calibration methods have little difference in the simulation accuracy of the watershed outlet,model performance indicators mostly are 0.8 and 0.6 for Nash Sutcliff Efficiency(NSE)and coefficient of determination(R~2)respectively,while Percent of Bias(PBIAS)is mostly lower than the minimum threshold of 15%;the SSSC is significantly better than the SMSC within the watershed,In the SMSC of Qingyang Station and Zhangjiashan Station,the effect of Qingyang drops most obviously with NSE and R~2 even below 0.5,while the simulation accuracy of Yangjiaping Station does not change much.The sensitivity of parameters obtained by the two methods was significantly different,parameter sensitivity in the SSSC is mainly affected by the hydrological characteristics of local catchment,while in the SMSC,the parameter sensitivity of downstream sites covering a larger spatial scale maintains a high consistency with the parameter sensitivity of nested upstream sites.(2)The annual water yield of the Jinghe River Basin is generally decreasing.The multi-year average annual water yield has shown a decreasing trend from southeast to northwest in space,and the yield of various sub-basins has a significant positive correlation,but the positive correlation shows a slight decline from 1980 to 2010.The water yield of the basin was decomposed by empirical orthogonal function(EOF),and it was found that the water yield of the basin was prone to form three spatial modalities:"regional consistent","north-south"and"central-north-centered",and the modal variance contribution rates are 77.68%,12.92%and 6.67%,respectively.At the same time,through the analysis of the rotating empirical orthogonal function(REOF),the watershed Water production is divided into four regions:the north-south regions,the central region,the eastern region,and the western region.The variance contribution rates of the four regional modes are36.2%,32.35%,23.42%,and 7.58%,respectively.(3)Using geographic detectors to detect the water yield and its influencing factors of the 119 sub-basins divided by the SWAT model,and find meteorological factors(potential evaporation,evaporation,precipitation)and proportion of land use factor(arable land,forest land,grassland,water area and construction)for the spatial variation of water yield with different degree of risk.Among them,the significant statistics of precipitation accounted for more than 70%of the total statistics,which had a high risk to the spatial distribution of water yield.The q value representing the explanatory ability of the spatial variation of water yield reached 0.561 at the precipitation factor,which contributed the most to the variation of water yield and was the driving factor of the spatial variation of water yield.Compared with other influencing factors,the influence of evaporation on water yield changes is significantly different.The interaction between meteorological factors has two-factor enhancement and nonlinear enhancement,and there is only nonlinear enhancement between land use factors and meteorological factors.Therefore,meteorological factors play a major role in the changes in water yield.When land-use factors and meteorological factors work together,land-use factors will enhance the impact of meteorological factors on the changes in water yield.(4)In the study area,the annual and monthly runoff coefficients show a decreasing trend with the increase of the catchment area.Except for the monthly runoff coefficient and the area from February to April,which have a power function decreasing relationship,the others are all exponential functions decreasing.The runoff coefficient in the dry season is greater than the runoff coefficient in the wet season,and the basin's strong groundwater replenishment capacity in winter makes the conversion of precipitation in the dry season into runoff relatively high;due to the spatial heterogeneity of precipitation,the difference in topography and vegetation,the runoff on a small scale The coefficient difference is even greater.Larger-scale watersheds have fewer sensitivity factors to runoff,which are mainly affected by climatic factors,while the effects of vegetation and land use factors are mainly reflected in small and medium-sized watersheds.