Analysis Of Water Balance In Yunyan River Basin Based On Vegetation Restorationon

The Loess Plateau is located in the middle of the transition from semi-humid regions to arid and semi-arid regions.It has less rainfall,large evapotranspiration,and serious soil erosion.Water resources have became the main factor restricting its ecological construction.In 1999,the implementation of projects,such as returning farmland to forest on the Loess Plateau promoted the restoration of vegetation ecology,greatly changed the original underlying surface conditions,greatly improved the vegetation coverage,and the original rainfall-infiltration-runoff-evaporation distribution relationship occurred Changes,the watershed water balance is affected.This paper selects the Yunyan River Basin,a typical watershed with vegetation restoration process in the loess area,calculates the water balance components of the watershed from 2001 to 2018.The evolution trend of each water balance component with vegetation restoration is analyzed to provide ecological hydrogeological basis for the rational use of water resources in the loess area,regional ecological balance and ecological sustainable development.The main discharge items in the watershed can be divided into three types: base flow,surface evapotranspiration and artificial extraction.The main recharge item is precipitation.In this paper,based on daily monitoring data of river basin runoff,remote sensing data,meteorological and topographic data,etc.the base flow automatic segmentation method,the evapotranspiration remote sensing inversion method based on the principle of surface energy balance,and the analysis and calculation of rainfall redistribution process were used.-Estimate runoff components,surface evapotranspiration and precipitation infiltration replenishment during 2018,and analyze the temporal evolution characteristics of runoff components and surface evapotranspiration,through Mann-Kendall analysis,double cumulative curve analysis,correlation analysis and other methods Explore the effects of human activities on excretory components.The analysis results show that: 1.The runoff and base flow show a downward trend from year to year,but the base flow index increases year by year;2.A large increase in vegetation coverage will cause a decrease in runoff and base flow,and it is the leading factor that causes its reduction;3.The surface evapotranspiration in the watershed showed an upward trend from year to year,and it was spatially higher in the west and lower in the east;4.NDVI value was significantly positively correlated with surface evapotranspiration,and the greater the NDVI value,the stronger the correlation between the two;5.The surface of different land use types The evapotranspiration data showed that forest land(2.04 mm/d)> grassland(1.65 mm/d)> cultivated land(1.52 mm/d).Based on the obtained data of each water balance component,combined with the vegetation coverage change data from 2001 to 2018,the responsiveness analysis and water balance calculation of each balance component to vegetation restoration are carried out.The analysis shows that: 1.There is a significant difference in the change trend of each equilibrium component with vegetation coverage.The watershed evapotranspiration and vegetation interception rate increased significantly with the increase of vegetation coverage.The watershed base flow,runoff and soil layer infiltration rate decreased with the increase of vegetation coverage,and the runoff showed a significant decrease.2.During the equilibrium period,the main source of water replenishment of the soil layer in the watershed is precipitation(99%),and the main discharge place is evapotranspiration(97%),and the soil layer water presents a negative equilibrium and is in a state of loss.