Balancing urban environmental and societal performance in high-density cities: Morphological trade-offs and optimization strategies in Shenzhen and Hong Kong

Achieving both environmental sustainability and societal prosperity in high-density cities remains a major planning challenge because the same urban form can improve one dimension while worsening the other. This study examines how urban form and land use shape these trade-offs in Shenzhen and Hong Kong, two compact but developmentally distinct cities in southern China. Using a 500 m grid, we measure environmental performance (EPI) from land surface temperature and carbon dioxide emissions, and societal performance (SPI) from night-time light intensity and population density. We then combine XGBoost and SHAP to identify the morphological features that most strongly influence EPI, SPI, and their combined eco-societal performance (ESPI). Three findings emerge. First, neighborhood-scale morphology plays a more consistent role than purely on-site form in shaping both environmental and societal performance, indicating that a block’s outcomes are strongly conditioned by the urban fabric in which it is embedded. Second, the dominant morphological constraint differs across the two cities. In Shenzhen, surrounding sky openness and building enclosure exert the strongest aggregate influence, whereas in Hong Kong, floor area ratio remains the decisive net driver, suggesting that the two cities require different morphological priorities for balancing environmental and societal goals. Third, Pareto-front analysis identifies mid-rise, mid-density blocks as the most reliably balanced typology, and counterfactual simulations on selected underperforming sites show that targeted increases in surrounding greenery and calibrated height adjustments can improve SPI by as much as 94% or EPI by up to 45% without necessarily sacrificing the other dimension. These findings show that improving sustainability in compact cities requires city-specific, neighborhood-scale interventions rather than one-size-fits-all densification or greening strategies. By linking morphological trade-offs with optimization-oriented planning guidance, this study provides an interpretable framework for identifying renewal priorities and reconciling environmental and societal objectives in high-density urban settings.