Optimizing vertical urban development: The role of a multidimensional assessment framework for balancing vertical growth and habitability

Rapid urbanization and population growth have driven vertical urban development in densely populated cities facing land scarcity. However, such pursuit towards high-density living often compromises the quality of the built environment and habitability, and accurately assessing its impacts is challenging, making it difficult for urban planners to identify optimal vertical growth strategies. Here we present a comprehensive assessment framework that integrates detailed 3D urban landscape models with Computational Fluid Dynamics (CFD) to multidimensionally assess customizable factors such as ventilation, thermal comfort, air quality, sunlight exposure, and urban aesthetics under different vertical growth scenarios. The framework is demonstrated through a case study to guide the vertical growth in a new development area in Hong Kong. Our simulations show that high-rise building clusters pose challenges such as strong winds, and trapped heat and air pollutants, but well-designed configurations of tall, slim buildings with adequate spacing can harness wind flow to improve thermal comfort and air quality. Despite a general deterioration of habitability being observed as vertical growth increases, there exists a threshold below which habitability is less impacted. This observation enables us to develop a Vertical Urban Habitability Index (VUHI) that can determine the optimal vertical growth by quantifying the trade-offs between increasing building areas and maintaining environmental habitability. The result shows that relaxing building heights by 7–13 % and plot ratios by 26–32 % beyond the government's benchmark can optimize urban development without compromising habitability. This framework not only serves as a reliable tool to guide vertical urban planning, but also facilitates benchmarking the habitability of different vertical cities, which enables knowledge sharing and identifies best practices for sustainable vertical development worldwide.