Anasua Chakraborty PhD
Unravelling the role of urban densification as a pragmatic strategy to achieve No Net Land Take 2050 - A futuristic Cellular Automata modelling for urban built-up scenarios
Supervisor: Prof. Jacques Teller
Abstract
Unprecedented urban growth has become a pressing challenge in the 21st century. More than half of the world’s population lives in urban areas, and this is expected to double by the year 2050. This surge has led to widespread land take through the conversion of agricultural and green spaces into built-up areas, often increasing travel distances and fragmenting natural habitats. To address these impacts, many cities are shifting towards urban densification, focusing on infill development to limit further expansion. The European Union’s goal of achieving No Net Land Take (NNLT) by 2050 stands as a bold ambition to promote compact growth. However, most studies have focused on (a) the theoretical analysis of the suggested policy regarding land take, (b) considering urban growth as a binary process to study urban expansion, and (c) conceptual evaluations of densification, with limited investigation into its real-world efficiency as a planning tool to manage urban expansion. Very little literature has quantitatively studied the impact of urban densification and its role in spatial planning strategies to achieve zero land take.
The main aims of this thesis are to: (i) understand the influencing factors behind urban expansion and densification, (ii) investigate the trajectories of historic demand trends of built-up development at a regional scale, (iii) model long-term urban development scenarios until 2050 to evaluate the efficiency of scenarios contributing to NNLT by 2050, and (iv) analyse the spatial distribution of urban built-up patterns across different NNLT scenarios.
To accomplish these objectives, the thesis first revisits the literature since 1971 to understand the role of Cellular Automata in modelling and predicting urban densification. Second, we conducted a base study through a comparative analysis of drivers impacting urban densification for cross-regional scenarios in the Brussels Metropolitan Area using a Multinomial Logistic Regression (MNL) model. In the third part, we analysed the model’s parameter sensitivity assessment and its impact on urban densification using a stepwise regression method. Finally, we developed a Cellular Automata (CA) model coupled with the MNL model to simulate urban growth scenarios: Business-As-Usual (BAU) and Growth-As-Usual (GAU). This study further extends to futuristic simulations of built-up areas under two additional scenarios: Densification Only (DO) and Centralities. The model includes long-term predictions for the BAU scenario—following historic trends; the GAU scenario—based on current observed demand; the DO scenario—a linear cessation of demand for expansion alongside an increase in densification; and the Centralities scenario—a demand allocation strategy focused on central zones predefined by the planning authorities of Wallonia. The formulation and integration of the GAU, DO, and Centralities scenarios represent the original contribution of this thesis to the field of urban densification modelling. The outcomes of these scenarios provide a holistic understanding of the impact, challenges, and prospects of urban densification as a solution to achieving NNLT.
Our results highlight the importance of considering a multi-level approach to understand the interplay between expansion and densification in urban development. Since the BAU and GAU scenarios do not follow any definite policy structure, an alternative framework is needed to address unregulated growth. Both the DO and Centralities scenarios can emerge as sustainable solutions to the land take issue by limiting the artificialization of green spaces through excessive construction. However, factors such as landowners’ resistance, changes in quality of living, and housing affordability may challenge the widespread adoption of urban densification. Decentralized planning and policy-making, or the intervention of municipal and supra-municipal bodies, should be encouraged to implement these spatial planning strategies effectively, paving the way for sustainable urban development. This thesis offers a detailed study of the role of urban densification in achieving NNLT by 2050 through spatial planning strategies, contributing to the broader goal of sustainable urban development.
