中国半干旱区呼包鄂城市群地表覆盖等级结构时空特征研究

Study on the Pattern of Land Cover Hierarchy in Hohhot-Baotou- Ordos Cities in the Semi-arid Region of China

以地处半干旱区的呼包鄂城市群为例,基于精确的建成区边界,采用决策树阈值分类模型与指数耦合模式,植被—不透水—土壤选取模型结合最小二乘像元混合分解模型等方法,构建半干旱区城市化过程中地表覆盖等级结构体系研究,从城市化—城市结构—城市组分揭示不同尺度21世纪以来的城市化过程。结果表明:①呼包鄂城市群2000～2015年的城市化过程较快,2005～2010年时段最为明显;总体空间格局呈现呼和浩特市外延式扩张,包头市填充式内展,鄂尔多斯市飞地式扩张为主;②不透水空间持续增加,在城区的占比由2000年的62.46%提升到2015年的75.40%;绿地空间呈现出波动变化的增加趋势,反映出半干旱区的城市化过程注重城市化与绿地协同建设;城市发展将裸土空间纳入,但城市化过程明显降低了裸土空间范围,有效提升了生态系统服务功能和人类福祉;③不透水组分密度变更顺序为低、中、高,增加明显的时段为2005～2010年;绿地组分呈现先降低后增加的变化特征,总体微幅增加,说明城区绿地得到提升;裸土组分密度呈现高、中、低的变化趋势,表明城市化扩张纳入了大量的裸土,随后裸土进一步转化为不透水面和植被,使城区内生态环境得到明显提升。总体而言,半干旱区的城市化过程可以有效降低周边裸土的面积,使其转化为可被利用的建筑和植被,有效改善区域水热环境和生态系统服务功能。

Taking the Hohhot-Baotou-Ordos city group in semiarid area as an example,constructs a system of surface hierarchical structure in the semi-arid area for urbanization.It reveals the urbanization process of different scales since twenty-first Century.The results show that:(1) the process of urbanization in the study area is intense in 2000~2015,especially during the period of 2005~2010.Among them,the expansion of Hohhot city presents extension type,Baotou for filling type,and ordos for enclaving type.(2) The impermeable space continued to increase(low density-medium density-high density increasing),and its proportion in urban areas increased from 62.46% in 2000 to 75.40% in 2015.The green space shows an increasing trend of fluctuation,which reflects that the urbanization process in semi-arid area focuses on the coordinated construction of urbanization and green space.Although the development of the city includes the bare soil space,the process of urbanization obviously reduces the spatial scope of the bare soil,which effectively improves the ecosystem service and human well-being.(3) the change order of impermeable components density is low,medium and high.During this period,the composition of the green space was reduced first and then increased,and the overall micro amplitude increased,indicating that the green space in the urban area was promoted.At the same time,the density of bare soil components showed a trend of high,middle and low,indicating that urbanization was expanded into a large number of bare soil.Then bare soil was further transformed into impervious surface and vegetation,and the ecological environment in the urban area was significantly improved.