| As the core element of economic growth,the allocation efficiency of land resources plays an important role in economic growth and achieving high-quality development.Irrational human exploitation of land resources has caused large-scale land degradation,making non-renewable resources increasingly depleted and the ecological environment increasingly degraded,endangering the survival and development of human beings.Therefore,studying the spatial and temporal characteristics of land use/cover changes in the region and exploring the influencing factors driving the changes in land use/cover types are crucial to promoting sustainable and high-quality development of land use in the region.With the successful completion of the Danjiangkou Dam Raising Project,the South-North Water Diversion Project was officially opened to water in 2014,and the land use/cover types in the core water source area have changed dramatically in both quantity and spatial distribution after the opening of water.The study of the spatial and temporal characteristics of land use/cover changes and their driving forces can provide theoretical support for the future development of the spatial pattern of land use in the core water source area,and promote the ecological and economic safety and high-quality development of the core water source area of the middle route of the South-North Water Diversion Project.This study first extracts the land use/cover data of the core water source area of the middle route of the South-North Water Diversion Project in consecutive years from 2008-2020 on Google Earth Engine platform and calculates the year-by-year land use/cover type area of each district and county;takes 2008,2014 and 2020 as the research time nodes,and uses Arc GIS10.6platform based on its Spatial analysis tools were used to obtain the conversion data between land use/cover types in the core water source area in two stages from 2008-2014 and 2014-2020,and the land use/cover transfer matrix was applied to study and analyze the spatial and temporal characteristics of land use/cover changes in the core water source area of the middle route of the South-North Water Diversion Project before and after the water connection in terms of quantitative structure and spatial structure.Secondly,the single land use/cover change dynamic attitude,comprehensive land use/cover change dynamic attitude and regional land use/cover type change trend and status index are introduced to analyze the land use/cover type change dynamics of the core water source area in each study period,so as to systematically analyze its land use/cover type change characteristic pattern.Finally,the PLUS model was used to investigate the driving factors affecting the land use/cover changes in the core water source area of the middle route of the South-North Water Diversion Project from the perspectives of natural,locational and socio-economic factors as well as policy and regulatory factors.The results of the study indicate that.(1)From 2008 to 2020,land use/cover in the core water source area of the middle route of the South-North Water Diversion Project was classified as farmland,forest,shrubs,grassland,water bodies,wasteland and impervious surface,with the largest proportion of forest area;followed by farmland and the smallest proportion of wasteland area.The area of forests,water bodies,wastelands and impervious surfaces showed an overall increasing trend during the study period,with a decrease in individual years,while the area of farmlands,shrubs and grasslands showed an overall decreasing trend,with an increase in individual years.The land use/cover change characteristics of the core water source area before and after the water connection from2008 to 2014 and from 2014 to 2020 were studied in segments,using the water connection of the South-North Water Diversion Project in 2014 as the critical point.Before the water connection,the impervious surface had the largest growth rate(25.35%)and the forest had the largest increase(265.53 km~2),in order of the magnitude of the change rate:impervious surface(25.35%),forest(2.41%),water bodies(-0.41%),agricultural land(-4.68%),grassland(-25.07%),and shrubs(-41.45%);after the water connection,the largest increase was in water bodies(335.15 km~2),the largest rate of change in wasteland(366.67%),and in order of magnitude of the rate of change,wasteland(366.67%),water bodies(53.88%),forest(2.64%),impervious surface(0.24%),agricultural land(-9.43%),shrubs(-19%),and grassland(-63.99%).(2)Before the water supply,a total of 1191.72 km~2 of land use/cover types in the core water source area were transferred to each other,among which the area of farmland was mainly transferred to forest(503.14 km~2)and impervious surface(73.78 km~2),the area of forest was mainly transferred to farmland(309.30 km~2),and the area of grassland was mainly transferred to farmland(84.92 km~2)and forest(71.99 km~2),indicating that the land use/cover changes in the core water source area before the water supply was passed were mainly the conversion of farmland and forest,while farmland was also partially converted to impervious surface;after the water supply was passed,a total of 1,401.98 km~2 of land use/cover types in the core water source area were transferred to each other,and the largest area transferred to other land use/cover types was farmland(834.39 km~2),indicates frequent conversion of farmland,and there is mutual conversion between forest and farmland,while the conversion of other land use/cover types is single,and the area of shrubs and grassland is mostly transferred out,and the area of water bodies is transferred in,with an increase of 338.60 km~2 and a decrease of 3.45km~2,with a net growth rate of 53.88%.The main reason is the expansion of Danjiangkou Reservoir and the expansion of water surface,which flooded the surrounding and upstream areas,and the area of water bodies in these areas increased and the area of other land use/cover types decreased.(3)The comprehensive land use dynamic attitude of the core water source area was 0.57%before and 0.68%after the water supply,which was greater after than before,indicating that the change of land use/cover type in the core water source area during the study period mainly came from after the water supply;the calculation results of the regional land use/cover type change trend and status index showed that although the core water source area was in equilibrium before and after the water supply,the equilibrium status after the water supply was worse than before.However,the equilibrium degree after the water supply is worse than that before the water supply,the equilibrium state of Maojian District and Yunyang District has changed for the better(the unbalanced state has risen to the balanced state),the state of Zhangwan District has remained in the quasi-balanced state in both periods,the state of Xichuan County has dropped from the quasi-balanced state to the unbalanced state,and the state of Danjiangkou City and Yunxi County has dropped from the balanced state to the unbalanced state,indicating that the land use/cover types of Xichuan County,Danjiangkou City and Utopia County have changed more drastically after the water supply.The changes in land use/cover types in Xichuan County,Danjiangkou City,and Yunxi County after the water supply was completed were more drastic and were related to a series of ecological protection of the water supply area to ensure the safety of water supply.(4)Driven by policy and regulatory factors,factors such as migration relocation,industrial restructuring,and ecological protection of water source areas promote changes in land use/cover types in the core water source areas of the middle route of the South-North Water Diversion Project.Driven by natural,locational and socio-economic factors,the drivers that contribute most to the increase in agricultural land and forest land before the water supply are GDP,and the drivers that contribute most to the increase in water bodies and impervious surfaces are distance from the reservoir and population density,respectively;after the water supply,the drivers that contribute most to the increase in agricultural land are elevation,the drivers that contribute most to the increase in forest land and water bodies are distance from the reservoir,and the drivers that contribute most to the increase in impervious surfaces are distance from the reservoir.The biggest driver for the increase in impervious surface is population density,indicating that the land use/cover types in the areas close to the reservoir are transformed to water bodies due to the raising of Danjiangkou Dam,and the impact on the change of land use/cover types in the water source area is also greater due to the promotion of the South-North Water Diversion Follow-up Project to ensure the ecological green development of the water source area. |
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