The growing negative impacts of urban sprawl arising from the rapid urbanization are a major challenge for sustainable urban development [1
]. Emphasizing sustainable development and ecological ideas of today, while determining how to effectively curb urban sprawl and harmonize the conflicts between the urban development and ecological protection or farmland preservation are the important issues concerning the human-dominated ecosystems [2
]. Among the various approaches to managing urban growth, urban containment policy has been extensively studied and introduced to many countries to increase urban land-use density and protect open space from being developed [4
]. Greenbelts, urban growth boundaries (UGBs), and urban service boundaries (USBs) are three major forms of urban containment policy [6
]. All of these forms aim to promote compact and contiguous development patterns, while preserving open space, agricultural land, and environmentally sensitive areas that are not currently suitable for urban development [4
]. However, among the notions of these urban containment boundaries, the UGBs have been widely discussed in academia and implemented in various countries around the world [7
], due to their popularity and easy acceptance.
In China, the conception of UGBs began to be known among the planners and scholars in the late 1990s [11
]. The officially issued “Urban Planning Compilation Methods” by China’s former Ministry of Construction, requires that the city master planning outline and central urban area planning include research of UGBs. The definitions for “prohibited construction areas”, “restricted construction areas”, and “suitable construction areas” were officially proposed. Also, the boundaries of urban construction areas were put forward. According to China’s Town and Country Planning Act initiated in 2008, the urban construction boundaries (UCBs), defined as legal boundaries to distinguish urban land from rural areas, were expected to constrain intensive human activities in aggregated urban settlements and thus maintain the ecosystem services provided by the surrounding seminatural and natural environment. Thus, in the context of rapid urbanization and pronounced environmental deterioration over the past three decades, it is urgent to reduce artificial adverse impacts on ecosystem functioning, maintain the harmony human–nature relationship, and sustain the development of the society across local, regional, and national scales [13
]. Meanwhile, UCBs are also applied by the urban planning administrative department as the basis for issuing construction site planning permits, and they have played a crucial role in constraining urban growth in China [1
]. Therefore, as the most explicit legal urban containment boundaries, the planned UCBs can be approximately defined as the UGBs under China’s Town and Country Planning Act.
In the process of delimiting UGBs, various factors related to urban spatial growth need to be considered. To date, conventional methods of delineating UGBs of Chinese cities are based on local authority’s intentions and planners’ personal experiences. Most of the time, they lack an adequate scientific basis and quantitative support. Consequently, the UGBs often fail to effectively contain urban expansion. According to the study of Han et al. (2009) on the verification of the implementation of planned UGBs of Beijing using multi-temporal remote sensing images, more urban land development was found outside than inside the UGBs during the two previous planning periods (1983–1993 and 1993–2005) [13
]. Tian et al. (2008) and Xu et al. (2009) also found that substantial urban development recently occurred beyond the UGBs of Guangzhou and Shanghai [14
]. The reason for the inconsistencies between the planned UGBs and the practical urban developments may be inadequate awareness of the rules and trends of urban growth. In addition, the conventional approach to establishing UGBs is not appropriate when taking into consideration the comprehensive forces that quantitatively influence urban growth process. However, comprehensive studies on the practice of UGBs in urban planning are still very limited. Therefore, new methods that can account for the key driving forces and accurately predict the trend of urban growth are necessary for improving the delimitation of UGBs.
Identifying the primary causes, processes, and trends of land-use change are crucial for supporting urban planning and delimiting urban growth boundaries [16
]. Land-use change models are useful tools for analyzing driving forces and processes, understanding the causes and consequences, and predicting the possible future outcomes of land-use change [18
]. Analysis of scenarios with land-use modeling can provide support for land-use planning [20
] and help inform policymakers of possible future patterns under different policy restraint conditions [23
]. As a typical spatially explicit and empirically based statistical model, the CLUE-S (the Conversion of Land Use and its Effects at Small regional extent) model treats the competition between different types of land uses based on systems theory, simulating different land uses simultaneously. It has been recognized as an excellent tool for to interpret land-use change processes [24
], and has been successfully applied to modeling of land-use change in many different regions. It can better account for the processes that determine changes in the spatial pattern of land use and explore possible future changes in urban growth at various spatial scales [27
]. It can also specify the conditions of scenarios for future land use in detail [28
]. Compared to the relatively subjective land-use models based on decision-making behavior of locators [30
], the CLUE-S model is based on land-use change processes and its simulation result is more objective and persuasive.
The CLUE-S model simulation results, as an alternative future urban form or a possible land-use scenario, can be applied as the basis for Chinese UGBs, which were schematically made with less scientific support and designed by the need of economic and population growth, and the planners’ experiences and topographical and geologic characteristics. The CLUE-S model can be conveniently applied to predict future land-use and urban growth patterns. In addition, the impact of the policies related to the control and guidance of urban growth can be simulated as different scenarios in the CLUE-S model. The model can be utilized as a planning support system to delimit UGBs. To our knowledge, there are extensive publications on land-use change simulation using the CLUE-S model. However, to date, case studies using the CLUE-S model simulation to establish UGBs have been relatively scarce.
This paper aims to bridge the gap between future land use, urban growth pattern, and UGBs by using the Xinzhuang town of Changshu city, eastern China, as an example. The objectives of this study are (1) to simulate future land-use changes and urban growth under different scenarios based on the CLUE-S model; and (2) to evaluate the feasibility and applicability of a land-use change model to support urban planning and delimit the UGBs. The paper is organized as follows. Firstly, we provide a detailed account and the implementation issues of the methodology. Secondly, the analysis of the simulation accuracy of CLUE-S model and future spatiotemporal changes of land use and urban growth under three scenarios are described. Thirdly, the simulated UGBs based on CLUE-S model are compared with the planned UGBs to evaluate the feasibility and applicability of land-use change model for supporting spatial planning. Finally, we discuss the deficiency of this research and present the conclusion. We intend our study to be helpful for urban planners and decision-makers for better understanding the complexities of land-use change so that they can make scientifically sound decisions for future urban growth boundaries.
China’s practice in delimitation of UGBs are often proven to be inefficient in curbing the uncontrolled urban expansion and associated adverse impacts on the surrounding environment. In this paper, the fast-growing Xinzhuang town of Changshu city, eastern China, was used as an example to demonstrate how to develop a new method towards delimiting UGBs based on a land-use change model (CLUE-S). The methodology adopted in this study can simulate possible patterns of urban growth and land-use change, and indicate how different policies, spatial restraints, and growth trends may or may not be conducive to the objectives of delimiting UGBs under different scenarios. The results show that the land-use change and urban growth simulation accuracy of CLUE-S model is high. The expansion of construction land and the decrease of paddy field would be the main changing trends of local land-use, and a massive area of cultivated land and ecological land providing ecosystem services would be transformed into construction land in 2009–2027. There is remarkable discordance in the spatial distribution between the simulated UGBs based on the CLUE-S model and the planned UGBs based on the conventional method, while the simulated results may more closely reflect the reality of urban growth laws. Herein, focusing on the future, UGBs may quite differ from the planned UGBs in the master planning, we consider that there is a strong need to develop an improved solution by using available historical data for land use, and configuration of model parameters during the calibration of the CLUE-S model. Only by doing these, can the enhanced land-use change models serve as scientific planning support tools that are helpful for assisting spatial planners and decision-makers to understand the urban growth process and delimit the UGBs. In the context of China’s reality, the findings would help local authorities better understand the complex land-use system and develop the improved urban development and land-use management, which can better balance urban expansion, basic farmland, and ecological land protection. In summary, this study proves that a land-use change model can provide the requisite theoretical guidance and technical support for delimiting and improving UGBs in Chinese cities. From a broad view, the findings of this study may provide beneficial lessons for our international colleagues who are engaged in urban planning, land development, spatial modeling, and ecosystem management.