Delineating urban growth boundaries under multi-objective and constraints

Highlights

• A novel framework is proposed for urban growth boundaries delineation.

• Optimization algorithm, carrying capacity analysis, and land-use suitability evaluation are integrated.

• Carrying capacity analysis ensures sustainable development for each sub-region and quantifies as constrains.

• Land-use suitability evaluates the potential of land-use functions and views as optimization objectives.

• The proposed framework can facilitate urban growth boundaries delineation.

Abstract

Urban growth boundaries (UGBs) have viewed as an efficient tool to control disorderly urban expansion and promote urban sustainable development. The existing methods related to UGBs delineation have also focused mainly on improving the efficiency and applicability of the methods. However, it is not enough to emphasize simply the superiority of the methods, especially in China. UGBs delineation not only considers regional heterogeneous resource endowments but also further coordinates pre-existing land-use plans and the conflicts with one another. The study presents a novel framework for delineating UGBs from carrying-capacity-oriented perspective whose contributions are twofold. Firstly, the level of carrying capacity on resource and environment for each sub-region was evaluated by carrying capacity analysis. A modified mechanism was used to coordinate the inter-regional trade-off between urban growth and carrying capacity on resource and environment and quantify as the constraints of the algorithm. The suitability evaluations of multiple land-use type, including urban lands, agricultural lands, and ecological lands, are viewed as the optimization objectives of the algorithm together with urban landscape compactness. Second, we develop a comprehensive method coupling carrying capacity analysis, land-use suitability evaluation, and modified ant colony optimization algorithm. It can not only coordinate the conflicts with the land-use plans but also ensure the sustainable development for each sub-region. The dilation and erosion algorithm generates optimal UGBs. The proposed framework was applied to UGBs delineation in Wuhan, a rapidly urbanizing city in China. Multi-scenarios UGBs were delineated by the proposed framework. The results demonstrated carrying-capacity-oriented UGBs delineation perspective is more practical and closer to reality than the results of traditional methods. The conceptual and methodological advancement of this study is applicable to other cities to assist UGBs delineation.

Introduction

Over the past four decades, most cities in China are experiencing a rapid urbanization process (Hoekstra & Wiedmann, 2014; Long, Han, Tu, & Shu, 2015; Wang, Jiao, Dong, Xu, & Xu, 2019). However, disorderly urban expansion caused a serious of problems, such as farmland loss, urban ecosystem degradation, the waste of urban lands and among others (Hoekstra & Wiedmann, 2014; He et al., 2018), which would pose a significant threat to sustainable urban development. Facing those circumstances, many cities worldwide have put forward urban containment policies as tools to guide orderly urban development and safeguard compactness. Greenbelts, urban growth boundaries (UGBs), and urban service boundaries (USBs) are the common-used practices in urban containment policies, among which the common and effective one is UGBs (He et al., 2018; Long, Han, Lai, & Mao, 2013).

Conventionally, UGBs describes the extent of urban expansion using regional development licenses and land use policies to guide the legal urban growth within the UGBs to control disorderly urban expansion (He et al., 2018). Many countries, such as USA, Switzerland, India and among others, view the UGBs as useful tools for government planning departments to promote the efficiency in urban management (Coiacetto, 2007; Gordon & Vipond, 2005; Hepinstall-Cymerman, Coe, & Hutyra, 2013; Knaap & Hopkins, 2001; Long et al., 2013; Tayyebi, Pijanowski, & Tayyebi, 2011). Researchers introduced UGBs into China in the early 21 st century, and the subsequent studies give close attention to UGBs in theory and practice (Long, He, & Liu, 2006; Long, Han, & Mao, 2009; Long et al., 2015). Moreover, China government also have been aware that UGBs is an efficient tool to control disorderly urban expansion. The exploration of UGBs delineation has launched during pilot projects for delineating UGBs in 14 rapidly growing cities in 2014, including Beijing, Guangzhou, among others. Likewise, researchers have also discussed the implementation procedure of UGBs delineation in Wuhan and Guangzhou (Xun et al., 2018; Xia, Zhang, Wang, & Yeh, 2019). Their goals were to introduce UGBs in urban planning to limit the disorderly urban expansion and the scope of construction in the city, more important, to serve as a relevant precedent for future nationwide UGBs delineation. Besides, the authoritative policy document in China was released to implement nationwide UGBs delineation (China’s State Council, 2019). The application of UGBs as an urban planning tool to control disorderly urban expansion and guide the smart growth of the city has gradually been recognized by Chinese government.

Urban expansion tends to result in encroachment on agricultural lands and ecological lands (Ke et al., 2018; Van Vliet, 2019). Obviously, in UGBs delineation, high-quality agricultural lands and superior ecological lands have the priority to be preserved. Likewise, the sub-regions with low carrying capacity on resource and environment should be assessed by the carry capacity analysis in favor of the maximum to mitigate the impact of urban growth on the regional ecosystem. The land-use suitability evaluation analyzes the suitability or importance of multiple land-use patterns, so as to find out location suitable for the corresponding land-use purposes, respectively. Therefore, it is necessary to introduce the carrying capacity analysis and land-use suitability evaluation into the algorithm to delineate UGBs. The corresponding UGBs will help minimize the impact of urban growth on the regional ecosystem. Standard technical guideline (Ministry Of Natural Resources of the People’s Republic of China, 2019) demonstrates the carrying capacity analysis evaluates the level of resources and environmental carrying capacity by the consideration of land resources, water resources, and environment and ecology condition; The land-use suitability evaluation mainly assesses the suitability for urban lands, agricultural production, and the importance of ecological protection. Their function is to analyze the suitability or importance of urban development lands, ecological lands, and agriculture lands, and thus determines the scale and scope of urban expansion based on carrying capacity level and its central objectives are similar to those established for previous research in ecological footprint and ecological capacity (Danish, Hassan, Baloch, Mehmood, & Zhang, 2019). Thus, the conceptual and methodological advancement of this study is applicable to other cities (or regions) to assist UGBs delineation.

Previous methods related to UGBs delineation include the “planar” expansion modeling and the “linear” expansion modeling (He et al., 2018). The former delineates UGBs by simulating urban dynamics in individual urban pixels (Li, Ma, Song, & Han, 2019; Xun et al., 2018; Zheng et al., 2017; Zhang, Liu, Lin, Zhang, & Zhang, 2020) while the latter treats UGBs as a single geometry and simulates the length expansion of the geometry in different azimuths to predict the future UGBs by setting up rules (He et al., 2018; Tayyebi, Perry, & Tayyebi, 2014; Xia et al., 2019; Zheng & Lv, 2016). These methods focused mainly on improving the efficiency and applicability of the methods. However, it is not enough to emphasize simply the superiority of the methods, especially in China. The corresponding UGBs may not be easily coordinated with pre-existing land-use plans, land-use status quo, and urban growth processes. Besides, the methods fail to consider spatial landscape characteristics, which will cause the inconvenience in urban management (Lin & Li, 2019). In China, the standard guidance provided a clear definition, types, principles, technical processes, and methodology in the delineation of UGBs (Ministry of Natural Resources of the People’s Republic of China, 2019). Wherein UGBs delineation in methodology is currently mainly conducted through a combination of land-use suitability evaluation, carrying capacity analysis, spatial overlaying analysis, and GIS mapping techniques. Although this method may be applied in future nationwide UGBs delineation, the results ignore the conflicts among the different land-use functions. Likewise, the combination method also ignores the spatial landscape characteristics.

Increasing numbers of studies show the spatial optimization methods have the potential to coordinate the conflicts among optimization objectives and consider the spatial landscape characteristics (Liu et al., 2015; Li & Parrott, 2016; Lin & Li, 2019; Zhao, Ma, Tang, & Liu, 2019). To break the management boundaries in planning bureaus, Chinese governments have replaced multiple related plans with territory spatial planning, so as to form the unique layout that can coordinate the conflicts among various land-use planning (China’s State Council, 2019). However, how to coordinate the conflicts still faces issues. Previous studies show that ant colony optimization (ACO) algorithm, which is a global heuristic optimization algorithm, has been proved to be an effective solution in land-use optimization problems, such as land-use allocation (Liu, Li, Shi, Huang, & Liu, 2012), natural reserve zoning (Li, Lao, Liu, & Chen, 2011), UGBs delineation (Ma, Li, & Cai, 2017), etc. In land-use optimization algorithms, the optimal land-use pattern is generated by setting the multiple optimization objective and constraints and configuring quantifiable parameters and operation procedures (Liu et al., 2012; Li & Parrott, 2016). The modified ACO algorithm was used to adapt to the urban land-use optimization problem. Besides, a modified mechanism (See Section 4.3 for details) incorporates results derived from carrying capacity analysis into the modified ACO algorithm as the macro-scale constraints of the algorithm. The results of land-use suitability evaluation are viewed as the optimization objectives of the algorithm together with urban landscape compactness. Such a coupling approach can efficiently incorporate carrying capacity analysis and land-use suitability evaluation into the ACO algorithm to optimize the urban land-use pattern. Consequently, the dilation and erosion algorithm was used to generate the final UGBs. In summary, the aims of this study were twofold: (1) to present a novel framework for UGBs delineation from the carrying-capacity-oriented perspective and (2) to develop a comprehensive method coupling carrying capacity analysis, land-use suitability evaluation, and a modified ACO algorithm. Those delineated UGBs can not only help minimize the impact of urban growth on the regional ecosystem but also coordinate the conflicts among multiple land-use functions. Wuhan was selected as the study area to assess our method with a 30-m resolution spatial data.