Response Of Soil Moisture To Precipitation And Water Balance Analysis Of Different Cover Types In Yulin Sandy Land

As an important carrier of the atmosphere-vegetation-soil continuum,soil moisture is a major player in the water cycle and plays a key role in the recovery and sustainable development of ecosystems,especially in arid and semi-arid regions where precipitation is much less than potential evapotranspiration.In this paper,the soil moisture changes of different cover types(bare land,grassland and salix)were studied to investigate the multi-year rainfall changes in the sandy area of Yulin,to analyze the soil moisture dynamics of bare land,grassland and salix and their response to rainfall,and to further analyze the water balance of the three,and to explore the remodeling process of soil hydrology by cover types.The main conclusions are as follows:(1)Precipitation and days of precipitation in Yuyang District from 1982 to 2021 showed a gradual increasing trend,with a change tendency rate of 43.1 mm/10 a and 3.1 days/10 a,respectively.rainfall distribution was more concentrated during the year,the rainfall is mainly concentrated in June to August,accounting for 59.7% of the annual precipitation and 43.5% of the annual precipitation days;it is mainly contributed by precipitation events of 0.1～9.9 mm and 10～24.9 mm levels,accounting for 32.4% and 32.9% of the total precipitation and 80.7%and 13.8% of the annual precipitation days,respectively.Through the analysis,2018 and 2019 are abundant water years,2020 and 2021 are dry water years.(2)Soil moisture of three cover types can be divided into stabilization period(December to February),accumulation period(March to May),depletion period(June to August)and recovery period(September to November),and precipitation recharge of soil moisture mainly occurs in the accumulation and recovery periods.Soil profile moisture showed significant spatial differentiation,with grassland being higher at 20 cm and salix land being higher at 50 cm and 150 cm.Grassland mainly utilized soil water at depths of 0～50 cm,and Salix mainly utilized soil water at 50～100 cm.Soil water response to precipitation was slower at shallow depths(0～50 cm)and faster at deeper depths(50～150 cm)than in bare land for both salix and grassland.The depth of precipitation recharge was significantly and positively correlated with precipitation amount,while the response lag time was significantly and positively correlated with precipitation ephemeris(p<0.05).The vegetation type,precipitation ephemeris,precipitation intensity,and freeze-thaw process influenced the redistribution of water in the soil profile and the succession of dominant vegetation types under changes in precipitation patterns.(3)Soil moisture transport models were established for grassland,salix and bare land,respectively,and the models were calibrated and validated,and the fitting effects were evaluated.The results showed that the soil moisture models under the three cover types had good fitting effects on the soil moisture content of the profiles,so the established numerical models could be used to simulate the soil moisture dynamics under different cover types in the study area.By simulating the response of soil moisture to precipitation,it can be seen that 20.4 mm precipitation would be able to recharge to 100 cm moisture in the bare land,so the bare land has higher moisture at 100 cm,grassland is affected by cover and root distribution,and precipitation at the level of light and moderate rain can only affect 20～50 cm,while the surface cover of Salix is less affected than grassland,and it is easy to form a preferential flow of roots,and the proportion of fine root distribution near 50 cm is denser than that of grassland.Therefore,the sample site has higher moisture in 50 cm～100 cm.(4)By simulating the soil water transport process under different cover types in 2018～2021,we found that the size of soil evapotranspiration was grassland>salix>bare land,and the water storage was bare land>salix>grassland.And the recharge size of seepage from different layers was bare land>salix>grassland,and it decreased with the deepening of soil layer and the decrease of rainfall.Due to the redistribution effect of vegetation on precipitation,bare land,grassland and sand willow had the largest average share of seepage water distribution below150 cm,20～50 cm and 50～100 cm layers,respectively;the seepage water at 20 cm and 50 cm depths of bare land,grassland and sand willow were highly significantly and positively correlated with cumulative rainfall at different time scales(p<0.01),and the seepage water at100 cm and The correlation coefficients of different layers gradually increased with the increase of time scale;while the correlation coefficients of daily,monthly and annual precipitation and seepage gradually decreased with the deepening of soil layer.(5)The water balance analysis shows that the rainfall in 2018 and 2019 has a certain recharge effect on 0～150 cm and deep soil water of different cover types,and the rainfall in2020 and 2021 can maintain the water balance of bare land,grassland and salix,and satisfy the basic evapotranspiration consumption of grassland and salix,although the recharge effect on deep layer is poor.In addition,Salix has a better ability to contain soil water and groundwater resources than grassland,and in dry years,Salix has a stronger ability to survive than grassland.