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

Unprecedented urban growth has been a pressing challenge in the 21st century. More than half of the world’s population lives in urban areas, which 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, studies mostly focus their research on the following: (a) theoretical analysis of the suggested policy regarding land take, (b) considering urban growth as a binary process to study urban expansion, and (c) focusing on 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 strategy to achieve zero land take.

The main aims of the thesis are to: (i) understand the influencing factors behind urban expansion and densification, (ii) investigate the trajectories of historic demand trend of built-up development at a regional scale, (iii) model the long term urban development scenarios till 2050 to evaluate the efficiency of scenarios contributing to NNLT by 2050, and (iv) analyse the spatial distribution of urban built-up patterns over the different NNLT scenarios.

In order to accomplish the aforementioned objectives, the thesis first revisits the literature since 1971 to understand the role of Cellular Automata in Modelling and Predicting Urban Densification. Second, we created a base study by a Comparative Analysis of Drivers Impacting Urban Densification for Cross-Regional Scenarios in Brussels Metropolitan Area using an Multinomial Logistic regression (MNL) Model. Hereto, in the third part, we analyse 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 MNL to simulate urban growth scenarios: Business-As-Usual (BAU) and Growth-As-Usual (GAU). This study further extends to the futuristic simulation of built-up under the two scenarios: Densification Only (DO) and Centralities. The model includes long-term prediction of the BAU scenario--following historic trend, the GAU scenario--following current observed demand, the DO scenario--a linear cessation of demand for expansion and increment in densification, and the Centralities--a demand allocation strategy in 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 outcome of these scenarios provides us with a holistic inference of the impact, challenges, and prospects of urban densification as a solution to NNLT.

Our results highlight the importance of considering a multi-level approach to understand the interplay of expansion and densification in urban development. Since the BAU and GAU scenarios do not adhere to any definite policy structure, an alternative framework is needed for situations of unregulated growth. DO and Centralities scenarios can both emerge as sustainable solutions against the land take issue, limiting the concrete construction--which leads to the artificialization of green spaces. However, aspects such as the landowners' resistance, changes in quality of living, and housing affordability can question the hegemonic nature of urban densification. Decentralised planning and polices, or interventions of municipal and supra-municipal bodies, should be encouraged to realise these spatial planning strategies, forming sustainable urban development. This thesis provides a detailed study of the role of urban densification in NNLT 2050, through spatial planning strategies that will aid in sustainable urban development.