中国建设用地的坡谱演化规律与爬坡影响

Evolution characteristics of slope spectrum and slope-climbing effects of built-up land in China

城镇建设用地规模与结构变化是国土空间开发与规划研究的基础。以往相关研究更关注建设用地水平空间扩张格局特征与模式,极少关注建设用地三维梯度上的“爬坡”特征规律与影响。因此,本文基于Google Earth Engine(GEE),并结合高精度地形数据与土地利用数据,在建设用地坡谱概念基础上,首次构建了平均建设用地爬坡指数(ABCI),系统地分析了1990—2018年中国建设用地坡谱在国家、区域、省级和城市4个尺度上的变化特征与规律并深入剖析建设用地爬坡的空间影响。结果显示:①1990—2018年中国坡度5°以上地区建设用地面积增长了1.43倍,比例由10.25%上升至14.81%。其中2010—2015年是建设用地爬坡发展最迅速与规模最大的时期,且中西部地区建设用地爬坡最为显著。②依据平均建设用地爬坡指数与上限坡度变化,可将中国34个省(自治区、直辖市)划分为高爬坡型、低爬坡型和水平扩展型3类,其中高爬坡型省份占50%以上,水平扩展型省份仅有7个,在空间上呈现“东南—西北”的两极分布特征。③1990—2010年爬坡型城市以山地与丘陵地貌城市为主,2010年后少数民族聚居区及低丘缓坡开发试点城市成为建设用地爬坡的主力。④建设用地爬坡在一定程度上能够减少建设用地扩张对平原优质耕地与生态用地的胁迫和侵占,缓解建设用地供需矛盾,但是无规划约束的开发和房地产驱动的“削山造地”则会导致地质灾害和生态环境风险的增加。

The changes in the scale and structure of built-up land is the basis for spatial development and planning of the national territory.Previous studies mainly focused on the characteristics and patterns of the horizontal expansion of built-up land,but little attention has been given to the"three-dimensional"gradient characteristics and effects of built-up land(such as slope-climbing).Therefore,based on Google Earth Engine,this study,for the first time as far as we know,uses DEM and land use data to draw built-up land slope spectrums and calculates the average built-up land climbing index(ABCI).The gradient characteristics and laws of the slope climbing of China's built-up land from 1990 to 2018 at the national,regional,provincial,and urban scales are systematically analyzed and the various spatial effects are explored.The results show that:(1)From 1990 to 2018,the area of built-up land with slope angle above 5°in China increased by 1.43 times,and the proportion of the total built-up land area rose from 10.25%to 14.81%.Particularly,the 2010-2015 period witnessed the fastest and largest slopeclimbing development of built-up land in China.Moreover,the slope-climbing intensities in the central and western regions are higher than that in other regions.(2)According to the average built-up land climbing index(ABCI)and the upper limited slope angle change(ULSC),the 34 provinces(autonomous regions and municipalities)in China can be divided into three types:high-climbing,low-climbing,and horizontally expanding.Among them,the number of highclimbing provinces accounts for more than 50%of the total.And seven horizontally-expanding provinces present the distribution characteristics of"southeast-northwest"in space.(3)Before 2010,the cities with slope-climbing phenomenon were mainly mountainous cities.However,ethnic minority settlements and low-hill and gentle slope development pilot cities became the main force for the slope-climbing of built-up land after 2010.(4)The slope-climbing of builtup land can reduce the occupation of plain arable land and ecological land by built-up land expansion to a certain extent,and thus alleviate the contradiction between supply and demand of build-up land.However,it is worth noting that development and construction without reasonable plans and bulldozing mountains to build cities driven by real estate can also lead to increased geological disasters and ecological risks.