Study On Soil Moisture Variation Characteristics Of Grassland Vegetation Under Urban Background

In order to reveal the change characteristics of soil moisture of grassland vegetation under the background of urbanization,based on the observation results of meteorological and grass soil moisture in Agricultural Water and Hydrology Ecology experimental field in Yangzijin campus of Yangzhou University,ten different rainfall events of different grades were selected to analyze the change process of soil moisture of grassland vegetation under different rainfall events,and the response characteristics of soil moisture in root layer of grassland vegetation to different rainfall events were revealed;the modified Penman-Monteith(P-M)formula recommended by FAO was used to calculate the reference crop evapotranspiration(ET0)in one hour step,Penman-Monteith formula was used to calculate the evapotranspiration(ET)of grassland in one hour step calibrated by the surface impedance(rs)of 0?30cm soil average water content and 10 cm soil water content respectively,and the water availability was evaluated;Hydrus-1D was used to simulate the soil water content at different depths,and the simulation results were evaluated with the measured soil water content,based on the Hydrus-1D simulation results,the rationality of rainfall infiltration depth in different rainfall events was tested.The main research results are as follows:(1)Among the ten selected rainfall events,the soil water content of 5cm changed in different degrees under all rainfall events,and the range of variation is related to rainfall intensity;generally,with the increase of rainfall,the change range of soil water content in 10cm increases;and the soil water content of 40cm does not change when the rainfall is small.The increasing rate of soil water content in root layer is related to rainfall intensity,and the higher the rainfall intensity,the faster the increasing rate of soil water content is.The infiltration rate of rainfall is greatly affected by the initial soil water content.The lower the initial surface water content is,the shorter the response time of soil water content to rainfall is.(2)During the calculation period(2020/01/01?2020/12/31),ETo accumulative value was 1101mm,accounting for 86%of the total rainfall(1282mm)in the same period.The mean value of ET0 in one-hour series was 0.125mm,and the maximum ET0 was 1.12mm.The sensitivity of ET0 to meteorological factors is as follows:wind speed>solar radiation>air temperature>relative humidity.(3)During the calculation period(2020/01/01?2020/12/31),the accumulated values of evapotranspiration(ET30,ET10)derived from surface impedance(rs)calibrated by average water content of 0?30cm soil and 10cm soil water content were 493 mm and 389mm respectively,and ET10 accounted for 79%of ET30,indicating that the water consumed by evapotranspiration of such grassland vegetation was mainly provided by the root layer(0?10cm);The diurnal and seasonal variations of ET were obvious.(4)The ma of root layer varied from 0.006 to 0.916,and the mean value is 0.37;the ma in the 0?30cm soil layer varied from 0.017 to 0.976,and the mean value is 0.47.The variation trend of ma in root layer and 0?30cm soil layer was similar,and the ma in root layer was slightly lower than that in 0-30cm soil layer in the same period,and the change of ma was mainly affected by ET.(5)Hydrus-1D was used to simulate soil moisture at different depths,during the simulation period(2020/05/01?2020/09/02),the root mean square error(RMSE)of measured and simulated soil water content at 10,25 and 40cm depths were 0.031,0.027 and 0.016,respectively,and the Nash efficiency coefficients(NSE)were 0.68,0.72 and 0.98,respectively,indicating that with the increase of soil depth,the fitting degree of simulation results and observation results is higher.(6)Hydrus-1D was used to simulate soil moisture under different rainfall events,the rainfall infiltration depth calculated by the simulation results is reasonable.In the absence of measured soil water content,rainfall data can be used to accurately calculate the rainfall infiltration depth in the study area by using Hydrus-1D.The results of this study are expected to provide some basic data for the further study of soil water movement of grassland vegetation under the background of urbanization.