Response Of Soil Water Storage To Cover Change And Precipitation In Small Basins Of Desert Wetlands

Artificial vegetation construction and sealing protection are the main measures for ecological construction in arid and semi-arid areas,while soil water,as a key limiting factor for vegetation restoration,is undoubtedly a hot issue of concern in theory and practice.It effectively reveals the response mechanism of soil water storage in watersheds to changes in land cover and precipitation,which is important for guiding vegetation restoration and reconstruction in desert areas.In this study,the Nanhaizi desert wetland small basin located in Yanchi County,Ningxia Province was selected as the research object.By using field observations,remote sensing image interpretation,and SWAT hydrological model simulations,this study analyzed the spatial and temporal evolution of soil water storage during vegetation construction and restoration at the watershed scale,and by simulating different vegetation pattern scenarios,the response mechanism of soil water storage in the watershed to the evolution of vegetation pattern is revealed.The conclusions of the study are as follows:(1)The shrubland in the watershed increased by 38.27%and natural grassland decreased by 173.22%from 1986 to 2021,and the two were transformed into each other during the 35 years.Artificial vegetation construction is the key factor to promote the land cover change in Nanhaizi desert wetland small basin.(2)In this study,the SWAT model of Nanhai small basin was established,and the calibration and validation of the model output daily runoff data were obtained:the R2 for the calibration period and validation period were 0.72 and 0.59,respectively;the NSE were 0.67 and 0.57,respectively;the percentage deviation PBIAS were less than 25%.The model simulated soil water storage was validated based on the measured soil moisture converted soil water storage data in the study area from 2021-2022.The R2 of the model validation was 0.56 and 0.79,respectively,indicating that the SWAT model can well characterize the trend of soil water storage in the watershed.(3)The trend of soil water storage in the basin during the year is consistent with the trend of precipitation,with obvious seasonality,and precipitation is the main source of soil water storage.The seasonal variability of both wind-sand and gray-calcium soils with precipitation shows corresponding seasonal changes,and the vertical variation of soil water storage varies among different soil types,with the largest intra-annual variation in surface soil water storage.The annual average values of soil water storage in 1986,2000,2010,and 2021 were 49.29 mm,41.37 mm,57.95 mm,and 42.39 mm for windsand soil and 30.64 mm,17.52 mm,34.20 mm,and 25.23 mm for gray-calcium soil,respectively,which indicated that the intra-annual variation of soil water storage in wind-sand soil was greater than that in gray-calcium soil.(4)Precipitation is the dominant factor causing changes in soil water storage in Nanhaizi small basin,but cover changes also have a non-negligible effect on changes in soil water storage。Rational allocation of trees,irrigation and grasses at the basin scale is important for soil water storage maintenance.The degree of response of soil water storage to precipitation in three vegetation types,namely,tree,irrigation and grass,decreases with increasing depth of soil layer.The seasonal variation of surface soil water storage is obvious,while the deep soil water storage and its variation are influenced by the vegetation type to a greater extent.