| The lack of water resources,fragile ecological environment and serious soil erosion in the hilly area of the Loess Plateau directly threaten the sustainable development of the social economy and ecological environment in the region,while the lack of soil water resources will affect vegetation growth and ecological construction,and further deteriorate the ecological environment.The loess plateau has deep soil layer and deep underground water.Therefore,precipitation is the only source of soil moisture in the hilly region of the loess plateau,and it is one of the important factors limiting vegetation growth.Meanwhile,it also affects the process of soil moisture consumption and recharge on the slope.This paper selects the Loess Plateau hilly Ansai runoff plots slope as the research area,based on on-line monitoring soil moisture and different depth of soil samples,studied the main factors affecting soil moisture dynamic change,expounds that the law of the soil moisture response to rainfall,simulated the change characteristics of soil moisture under different conditions of rainfall and slope soil water consumption and compensation mode and provides a scientific basis for the efficient utilization of soil water resources and vegetation restoration in the hilly region of the loess plateau.The main conclusions are as follows:(1)The response process of soil moisture to rainfall was analyzed based on the measured data The response depth of soil moisture to different rainfall types is different.Light rain causes the increase of soil moisture in shallow layer(10?40cm),while moderate rain causes the increase of soil moisture in soil layer(20?60cm),and heavy rain could cause the increase of the deep soil moisture.Under the same rainfall condition,the response depth of soil moisture in slope farmland to rainfall was deeper and faster,followed by that of grassland,and that of forest land was shallowest and slowest.The phenomenon becomes more pronounced with greater rainfall.The process of soil moisture regression after rainfall is related to land use type,soil texture and rainfall intensity.After the rainfall,the soil moisture regression showed a diurnal trend,and the soil moisture regression rate increased during the day,while decreased at night.The regression rate of soil moisture in slope farmland,forest land and grassland was different.The average retreat rate of soil moisture after rainfall was generally shown as follows:Grassland>slope farmland>forest land.(2)The main factors affecting the dynamic change of soil moisture were identified.The influence of environmental factors on soil moisture changes was analyzed based on the grey correlation method.The influence of environmental factors on soil moisture changes was analyzed based on the grey correlation method.In the no-rain period,the most influential factors of soil moisture in the shallow and middle soil layers of the three types of land use are the daily average relative humidity,while the most important factor affecting the deep soil moisture is the soil temperature;During the rainfall period,the most important factors affecting soil moisture in the three land use types are the soil moisture in the early stage,followed by the daily average relative humidity.(3)The Hydrus model can well simulate the soil moisture change process on different slopes in the study area.HYDRUS-1D simulation process of soil water infiltration under different rainfall conditions the decisive coefficient R2 were greater than 0.7,the relative error less than 2.0%,soil moisture simulation values can accurately reflect the different land use types change trend of soil water content and depth over time,the result is reliable,can be applied to soil moisture simulation and prediction in the region.Based on the verified model to simulate the dynamic change of water under different rainfall conditions,the rainfall intensity and rainfall duration have an effect on the dynamic change of soil moisture,and the infiltration depth of water content was different under different rainfall conditions.(4)Revealed the soil water consumption and compensation mechanism on the slope of the Loess Plateau hilly area.The annual variation of soil water storage can be divided into three periods:soil water consumption period(April to June),soil water recovery period(July to October)and soil moisture stability period(November to March).Soil water deficit in different land use showed seasonal variation.Different land use types from April to June,the soil water storage deficit is grassland>forest land>slope farmland.The loss of soil water storage from July to October is:forest land>grassland>slope farmland.At the end of the rainy season,the soil water storage deficits of all three land use types were positive,indicating that the compensation for soil moisture was greater than the soil water consumption,and the soil water storage deficit was effectively compensated throughout the rainy season. |
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