Response Of Soil Moisture To Precipitation On The Micro-topography Of Loess Slope In Northern Shaanxi

Soil moisture is the main factor restricting the construction of forest and grass vegetation on steep slopes in the loess region of northern Shaanxi,precipitation is the only source of soil moisture in this area,and precipitation can be secondarily distributed by micro-topography to affect soil moisture content.Therefore,in this paper,Wuqi County in northern Shaanxi Province was selected as the representative research area,and taking the micro-topography of steep slopes as the research object in loess slopes of northern Shaanxi.The moving average method,Mann-Kendall test and wavelet analysis were used to analyze the characteristics of the multi-year precipitation change in the study area,to clarify the trend and cycle of multi-year precipitation change.Combined with the soil moisture data by field survey,the dynamic process of soil moisture was analyzed,Pearson correlation and gray correlation analysis method were respectively used to explore the relationship between micro-topography soil moisture and precipitation under different hydrological years and the degree of correlation between the previous year's precipitation characteristic value and the current year's soil moisture.Finally,revealing the response characteristics of micro-topography soil moisture to precipitation on the loess slopes in northern Shaanxi,and provided a theoretical basis for the rational use of water resources and the plant community structure configuration of forest and grass vegetation construction in this area.The main conclusions of this paper are as follows:(1)The multi-year precipitation trend in the research area is as follows: interannual precipitation fluctuates between 270.00mm-787.50 mm,and shows a decreasing trend with a reduction of 11.30mm/10 a.Seasonal precipitation also shows a decrease of different magnitudes,the dry season precipitation has the largest reduction(9.23mm/10a),the second in the rainy season(1.82mm/10a),the smallest reduction in winter snowfall(0.25mm/10a).The annual and seasonal precipitation have obvious periodic fluctuations.The 28 a characteristic time scale mainly controls the annual precipitation fluctuations in the study area,and the fluctuation period is about 18 years.The time characteristic scales that control the precipitation fluctuations in the rainy season,dry season,and winter are respectively 28 a,10a,and 26 a,and the corresponding fluctuation periods are 18 years,7 years,and 17 years.(2)Analysis of the soil moisture characteristics of various types of micro-topography and original slope surface under different precipitation years found that the scarp and original slope surface have low water storage efficiency during the growing season in dry year,and the rainfall supply cannot meet the soil moisture of the scarp and original slope surface consumption.Secondly,the precipitation storage efficiency of micro-topography in the growing season shows gully(22.60%)> shallow gully(20.42%)> platform(18.69%)> collapse(18.31%)> original slope surface(11.97%)> scarp(10.53%).The soil water content of each micro-topography generally showed a trend of decreasing first and then increasing with the increase of soil depth under the three types of precipitation years.(3)With the change of annual precipitation,the replenishment efficiency of precipitation to different layers of soil moisture in micro-topography is different.Dry year precipitation is beneficial to replenish surface layers(0-20cm)soil moisture in shallow gully and platform,and it is beneficial to replenish 40-60 cm soil moisture in collapse,scarp and gully,original slope surface soil moisture are all in the range of 20-40 cm.Normal precipitation year is beneficial to replenish 40-60 cm soil moisture in collapse,platform and gully,and which is conducive to replenish shallow gully,scarp,original slope surface soil moisture at 60-80 cm,100-120 cm and 80-100 cm respectively.High flow year is beneficial to replenish 60-80 cm soil moisture in collapse and gully,and it is beneficial to replenish 80-100 cm soil moisture in platform and original slope surface,shallow gully and scarp soil moisture are respective all in the range of 120-140 cm and 40-60 cm.(4)The previous year's annual precipitation has a greater impact on shallow gully,gully,scarp and collapse then soil moisture than other precipitation features.The rainfall of the previous year's rainy season has a greater impact on the soil moisture of the platform and original slope surface during that time than other precipitation features.