| Loess Plateau is located in semi-arid and semi-humid areas,with special soil structure and deep water table,so soil water is very important for vegetation growth.Since 1999,the Loess Plateau has been carrying out the project of returning farmland to forest（grass）.During the implementation of the project,the fallow vegetation may overconsume soil water and cause ecological environment changes.Therefore,it is significant to study the influence on soil water during the vegetation restoration process.In this study,based on remote sensing monitoring land use/cover and soil moisture fusion product data,land use transfer matrix,transfer mapping and change magnitude were used to analyze the spatial and temporal changes of land use on the Loess Plateau from 2000 to 2020,and the Theil-Sen Median slope estimation and Mann-Kendal trend analysis were used to study the spatial and temporal changes of soil water on the Loess Plateau from 2000 to 2020.The spatial and temporal changes of land use on the Loess Plateau from 2000 to 2020 were studied,based on which the effects of vegetation restoration on soil moisture on the Loess Plateau were further analyzed.The main results obtained are as follows（1）The changes of arable land,forest land and unused land on the Loess Plateau from2000 to 2020 are obvious,with arable land decreasing by 12,918 km2（accounting for 6%of the total arable land area）,forest land increasing by 3,232 km2（accounting for 6%of the total arable land area）,shrubs increasing by 555 km2（accounting for 1.4%of the total shrub area）,and unused land decreasing by 1,982 km2（accounting for 5%of the total unused land area）;during the recent During the last 20a,arable land mainly shifted to grassland,with an area of 58,576km2（28%of the total arable land area）,mainly in the semi-arid central Shaanxi and Shanxi;forest land mainly shifted to grassland and arable land,with an area of10,599km2（20%of the total forest land area）and 6,890km2（13%of the total forest land area）,mainly in the semi-arid and semi-humid areas;shrubland mainly shifted to grassland,with an area of 11,088 km2（13%of the total area of shrubland）.km2（28%of the total shrubland area）,mainly in Yan’an City,Shanxi Province,and Shanxi Province in the semi-arid zone;grassland is mainly transferred to cropland,with an area of 54,923 km2（28%of the total grassland area）.km2（21%of the total area of grassland）,mainly located in semi-arid areas,and the transfer of unused land mainly to grassland,with a transfer area of10,278 km2（24%of the total area of unused land）,mainly occurring in Inner Mongolia and eastern Qinghai to grassland.（2）Soil moisture in the Loess Plateau showed an overall increasing trend(4.9×10-4yr-1)during the growing season from 2000 to 2020,and soil moisture trends in all climatic zones were consistent with the Loess Plateau,with an overall increasing trend,but with slightly different rates of rise,with the semi-arid zone being the fastest(6.1×10-4yr-1),the arid zone the second fastest(4.4×10-4yr-1),and the semi-humid zone the slowest(1.8×10-4yr-1).Soil moisture in the Loess Plateau in spring,summer,autumn and winter show fluctuating rising trend,but the rising rate is slightly different,from large to small,spring>summer>autumn>winter;soil moisture in the growing season of the Loess Plateau from 2000 to2020 showed rising trend in 73%of the area,rising area of 459809km2,mainly in Gansu,Ningxia and part of Inner Mongolia region.Among them,23%of the regions showed a highly significant rising trend,with a regional area of 142,370 km2,mainly distributed in Ningxia,Gansu and Qinghai regions.（3）The growing season soil moisture of untransformed land types all showed an increasing trend from 2000 to 2020,with shrubs showing the largest increasing trend(8.8×10-4yr-1),followed by woodland(6.7×10-4yr-1)and cultivated land the smallest(1.3×10-4yr-1).However,the process fluctuated slightly,with soil moisture showing a trend of decreasing and then increasing,decreasing in the time period 2000-2009 and increasing in 2009-2020.soil moisture varied in the growing seasons of different vegetation restoration methods from 2000-2020,with soil moisture increasing when transforming from cropland to woodland,shrubland and grassland,with shrubland rising the fastest,followed by woodland and grassland the slowest.The trend of soil moisture change from unutilized to forested land was opposite to that of unutilized to grassland,and the overall trend of soil moisture increase from unutilized to grassland(8×10-4yr-1),in which the trend of soil moisture increase was higher after 2010.The soil moisture in the transition from unutilized to forested land first increased and then decreased,with a decreasing trend from 2000 to2010(1.6×10-3yr-1)and an increasing trend from 2010 to 2010(2.1×10-3yr-1),and an overall fluctuating decreasing trend(1.2×10-3yr-1). |
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