The team chose two deliberately contrasting case cities: Hong Kong and Zurich. Hong Kong is one of the densest vertical metropolises on Earth, a subtropical city where compact high-rise development presses against steep green terrain and a heavily engineered coastline. Zurich, by contrast, is a mid-sized European city with a temperate climate, lower densities, and a long tradition of green infrastructure planning. If consistent form–function relationships could be detected across two such different urban contexts, the researchers reasoned, those relationships would be far more convincing as general principles of sustainable urban design than findings drawn from a single city.

To capture multifunctionality, the study analyzed five key urban functions spanning social, ecological, and infrastructure domains: heat mitigation, pluvial flood regulation, bird diversity, a mortality-derived health outcome, and small business vitality. This selection is significant because most previous studies have evaluated urban functions in isolation—asking, for example, how tree canopy affects temperature, or how street connectivity affects commerce—without examining how the same physical features perform across multiple functions simultaneously. By assessing several functions together, the researchers could identify where benefits align into synergies and where they collide into trade-offs, the two currencies of multifunctional assessment.

The technical heart of the study lies in characterizing urban form and linking it statistically to each function across the two cities. Urban form descriptors included the coverage of impervious surfaces such as asphalt, concrete, and rooftops; the configuration of green space, including the size and shape irregularity of green patches; and the proximity of urban locations to water bodies. Each of these form variables was then associated with spatially explicit measures of the five functions, allowing the team to compare the direction, magnitude, and spatial heterogeneity of relationships in Hong Kong against those in Zurich. This comparative framework, built around a clearly defined and representative indicator set, is one of the study’s principal methodological contributions.

Some results were strikingly consistent across both cities. Increased impervious surface coverage was negatively associated with both pluvial flood regulation and heat mitigation—hardly a surprise to urban climatologists and hydrologists, since sealed surfaces prevent rainfall infiltration and store and re-emit heat—but the consistency of the signal in two climatically and morphologically different cities strengthens the case that reducing impervious cover is a robust, transferable design lever. Conversely, proximity to water was positively associated with both flood and heat mitigation functions, and was tentatively associated with the mortality-derived health outcome as well. Water, in other words, emerged as a rare form element whose benefits appear to ripple across multiple domains at once, echoing the growing international interest in blue-green infrastructure.

Green space, however, told a more complicated and arguably more interesting story. Rather than acting as a universal good, the form of green space was associated with urban functions in diverse ways that can involve genuine trade-offs. The most vivid example reported in the study concerns patch shape: irregular green patches—those with convoluted, ragged edges rather than compact outlines—were associated with higher bird diversity but lower pluvial flood mitigation capacity. Ecologists have long known that complex habitat edges can support richer avian communities, but the same irregular geometry appears to diminish the hydrological performance of green areas. For planners, this means a single prescription such as add more greenery cannot be applied blindly; the geometry of that greenery matters, and it matters differently for different functions.

Although the overall direction of the form–function relationships was generally consistent between Hong Kong and Zurich, the magnitude and spatial heterogeneity of those relationships differed, and the authors relate these differences to city-specific characteristics. In practical terms, the same increment of impervious surface or the same change in green patch configuration does not buy or cost the same amount of cooling, drainage capacity, biodiversity, health benefit, or commercial vitality in a subtropical vertical city as it does in a temperate European one. Local climate, topography, building morphology, and existing ecological conditions all modulate how strongly a given form element expresses its functional consequences. This is a caution against copy-pasting design guidelines across continents, but also an argument for the kind of diagnostic, city-specific assessment the study’s framework enables.

The inclusion of mortality-derived health outcomes and small business vitality alongside the more conventional ecological and hydrological indicators is what gives the study its cross-domain ambition. Heat and flooding are environmental hazards; bird diversity is an ecological signature; but mortality-based health measures and the vitality of small businesses are profoundly human concerns. By showing that urban form is simultaneously associated with functions within and across these ecological and human domains, the study makes the case that the city is best understood as an integrated system in which a planning decision in one domain inevitably transmits consequences into others. A street tree strategy is a public health strategy is, potentially, an economic strategy.

For practitioners, the implications are twofold. First, synergies should be actively hunted: form elements such as water proximity, which appear to deliver benefits across several functions, represent high-leverage interventions in the urban fabric. Second, trade-offs must be made explicit and balanced deliberately rather than discovered after the fact. The study’s multifunctional assessment framework provides a template for doing exactly that—mapping where functions align and conflict within a defined indicator set, and using those maps to guide zoning, greening, and infrastructure decisions. As cities worldwide confront intensifying heat, more extreme rainfall, biodiversity loss, and economic pressure on neighborhood commerce, the message of this research is that the shape of the city is not a neutral backdrop but an active determinant of how many things a city can do well at once.

The work was funded in part by the Future Cities Lab Global programme, supported by the National Research Foundation of Singapore under its CREATE programme and ETH Zurich, with contributions from the National University of Singapore, Nanyang Technological University, and the Singapore University of Technology and Design, and Yue Zhu received additional support from the Science and Technology Development Fund of the Macao SAR. Published open access in npj Urban Sustainability, the study establishes a comparative foundation that other cities can adapt—provided they respect the central lesson of Hong Kong and Zurich: the relationships are real and repeatable, but their strength and spatial texture are always local.

Subject of Research: Associations between urban form and multifunctionality across ecological and human urban functions in Hong Kong and Zurich

Article Title: Associations between urban form and urban multifunctionality: a comparative study

Article References: Zhu, Y., Burlando, P., Zhang, Y., Huang, J., Chi, D., Wang, J., Qiu, Y., Manoli, G., Fatichi, S., & Tan, P. Y. (2026). Associations between urban form and urban multifunctionality: a comparative study. npj Urban Sustainability. https://doi.org/10.1038/s42949-026-00481-3

Image Credits: AI Generated

DOI: 10.1038/s42949-026-00481-3

Keywords: urban form, urban multifunctionality, heat mitigation, pluvial flood regulation, bird diversity, green space, impervious surfaces, blue-green infrastructure, Hong Kong, Zurich, urban sustainability, comparative study