Dynamic Change Of Soil Moisture And Numerical Simulation Of Its Movement On The Slope Scale In Zhifanggou Watershed

Soil moisture is one of the most important factors which affect the survival of vegetation.In recent years,with the rapid development of regional economy and society,a serious conflict of water supply and demand arise,especially in the northwestern arid and semi-arid region of Loess Plateau.Therefore,the study on the distribution of soil moisture and its dynamic change is conducive to revealing the effects of the influencing factors on soil water and their mechanisms,as well as providing theoretical support for regional soil water management,vegetation restoration and soil erosion control,and is of great significance to improve the ecological environment of arid area.The primary objective of this study is to estimate the spatial distribution characteristics,spatial heterogeneity and main influencing factors of soil moisture and the numerical simulation of soil moisture movement of Zhifanggou Watershed.Incorporating the observed soil moisture of 0~160cm depth in 7 runoff fields under different slopes and different vegetation cover types,the measured data such as rainfall and evapotranspiration,the spatial distribution characteristics and spatial heterogeneity of soil moisture were analyzed from slope scales,as well as its main influencing factors.Firstly,the spatial distribution characteristics of soil moisture in different growth stages of maize and potato were analyzed by the measured data of soil moisture,and the main influencing factors of soil moisture were studied through canonical correspondence analysis(CCA)ordination methods.Secondly,the soil water storage capacity of different depths was calculated to analyze the spatial and temporal variability of the soil water storage capacity.Finally,HYDRUS software was used to simulate soil moisture migration.The stimulation values are consistent with the measured values.The RMSE values of each layer are small and the AVRE values are close to 1,which shows that the simulation results are well.The main conclusions are as follows:1.In the early period of vegetation growth,the vegetation grows slowly and the water requirement is small.And with the growth and development of the plants,the demand for water is gradually increasing.During the growth and development of corn,the jointing-heading-fillling stages need most water,while for potato,it is the tuber bulking stage.In the same soil layer,the soil water content is different at different stages of vegetation growth.Among them,the most obvious soil moisture variation is 0~60cm depth soil layer.2.From the vertical direction,the distribution of soil moisture in each runoff field has a certain degree of similarity,showing an increase and then decrease trend with the increase of soil depth.In the horizontal direction,the soil moisture at the low slope(5°,10°,and 15°)flow field decreased first and then increased,while the high slope(25°)first increased and then decreased.3.Slope and vegetation cover types have significant effects on soil moisture content at different depths,but the impact mainly occurs in shallow soil layers.Relatively speaking,the effect of vegetation cover type on depth of soil moisture content is deeper than that of slope,and the accumulation effect of soil moisture on the slope bottom is not obvious in the 0~160cm depth profile.4.According to the multivariate analysis of variance and canonical correspondence analysis(CCA)result of environmental factors of soil moisture,it can be seen that the relative order of the effects of the three factors on soil moisture is: slope(29)vegetation cover type(29)slope position.5.The coefficient of variation of soil water storage at all depths ranges from 0.11 to 0.20 at each measurement time,which means soil water storage is in the middle intensity.The water storage capacity in the soil layers of 40~100cm and 100~160cm depth in the study area was significantly higher than that of 0~40cm depth(p<0.05),while there was no significant difference between 40~100cm and 100–160cm depth.The soil water storage shows significant spatial autocorrelation at each depth range.The rate of structural variation in each layer accounted for more than 75% of the total variation,which means the spatial autocorrelation is strong.And,in each period,the spatial autocorrelation of soil moisture shows the trend of first decrease and following increase with the increase of soil depth.6.The stimulation values of HYDRUS software are consistent with the measured values.The RMSE values of each layer are small and the AVRE values are close to 1,which shows that the simulation results are well.The PRMSE values of 0~40 cm depth are more than 20% and the PRMSE values of 40~160 cm depth are less than 20%,indicating that the simulation accuracy is higher in 40~160 cm depth.