城市扩张情景模拟及对城市形态与体系的影响——以广西西江经济带为例

针对区域层面城市扩张模拟研究的缺失,以快速城市化的广西西江经济带为案例区,构建了生态重要性和土地开发建设适宜性两种扩张情景;借助最小累积阻力模型对经济带内主要城市的扩张进行情景模拟,进而分析城市扩张对其形态和位序—规模特征的影响,揭示不同情境间的差异。结果表明,随着扩张强度增加,城市形态趋于紧凑和稳定,城市位序—规模发生变化。对比两种情景,生态重要性情境下,新增建设用地的分配相对均匀,首位城市发生变化,首位度明显下降,城市扩张方式多样,形态较为复杂、松散,内部各城市之间形状差异较大;土地开发建设适宜性情景下,大中城市扩张速度较快,首位城市保持不变,其首位度略有下降,城市扩张以外延式和填充式扩张为主,形态相对紧凑、规则,各城市间形状差异较小。研究认为基于生态重要性的城市扩张情景有利于减少重要生态空间占用、维护城市生态系统健康、合理调控城市体系结构,是一种更加可持续的扩张方式。

Scenario simulation of regional urban expansion and effects on urban form and system：A case study of Xijiang River Economic Belt in Guangxi

Previous research focused on urban expansion of individual city mostly, and less attention was paid to urban expansion at a regional level, especially in rapidly developing regions. Aiming at enriching the research fields of urban expansion and covering the shortage of regional-level research, Xijiang River Economic Belt in Guangxi (GXEB for short) was chosen as the study case to examine urban expansion simulation and its effects at the regional level. The minimum cumulative resistance model (MCR for short) was adopted and all urban areas of the whole region were chosen as the sources of urban expansion. Two kinds of resistance surfaces were designed based on spatial evaluation results of regional Ecological Importance and land Construction Suitability (EI and CS for short respectively). The effects of urban expansion on urban form and regional rank-size structure of urban system structure were analyzed, and the differences between two scenarios were also studied. Results indicated that urban form tended to be more compact and stable with the increasing intensity of urban expansion, and the rank-size also changed. However, there were significant differences between EI and CS scenarios. Under the EI scenario, the newly-added construction lands were relatively evenly distributed to all cities in this area, causing the change of primary city from Nanning city to Binyang county and the decline of primacy ratio. The types of urban expansion are more diverse, which caused the significant difference of urban form and the trend of becoming more and more complex and incompact. Under the CS scenario, larger cities dominated the expansion of newly-added construction lands. Although the primacy ratio tended to decline slightly, Nanning kept the role of primary city. Extension and infilling dominated the type of urban expansion, causing relatively compact, regular and similar urban form. In comparison of the results and effects of EI and CS scenarios, the EI scenario was of significant advantage in reducing occupation of important ecological spaces, maintaining the health of urban eco-system and regulating the structure of regional urban system, and was a more sustainable expanding scenario.