Green walls cool cities and create urban habitats

Urban areas face rising temperatures and shrinking green spaces. Cities replace natural landscapes with concrete, making heat waves more intense. Wildlife struggles to find habitats, leading to biodiversity loss.

In response, architects and ecologists explore solutions to make cities more livable. Green walls have emerged as a promising option.

These plant-covered facades do more than make buildings look better. They help cool urban areas and provide essential habitats for birds, insects, and other organisms.

A recent study led by Utrecht University ecologist Katharina Hecht provides scientific evidence of these benefits. The research compares green walls with bare walls and natural cliffs, shedding light on their ecological value.

Insights into green walls

The study, published in the journal Building and Environment, highlights the impact of green walls on urban cooling and biodiversity.

Hecht and her team worked with researchers from Singapore’s Nanyang Technological University and the Singapore-based company bioSEA. Together, they examined 20 green walls in Singapore’s urban environment.

“Green walls can be much more than just a decorative trend,” said Hecht. Many construction companies and policymakers promote them, but solid scientific evidence has been lacking.

Cooling effects in cities

One of the study’s key findings is the ability of these walls to reduce temperatures. The researchers measured a cooling effect of up to 0.6–0.7 degrees Celsius between the front and back sides of these walls.

“This might sound like a small difference. But in the context of urban heat, even small reductions can lower energy costs and make buildings more comfortable to live and work in,” said Hecht.

With increasing numbers of green walls, this cooling effect could help combat the urban heat island phenomenon.

Urban heat islands occur when cities absorb and retain heat, making them significantly warmer than surrounding rural areas. Green walls provide shade, reduce heat absorption, and improve thermal comfort in dense urban settings.

They also contribute to climate resilience by lowering reliance on air conditioning, reducing energy consumption.

Supporting urban biodiversity with green walls

Beyond cooling, green walls also enhance urban biodiversity. The researchers found that plant-covered facades hosted over 100 animal species, including insects, spiders, and birds. This is a stark contrast to non-vegetated walls, which support only a handful of species.

The study also compared green walls to natural cliffs to assess their effectiveness in replicating natural habitats. Natural cliffs, unsurprisingly, supported slightly more biodiversity. However, green walls still provided valuable shelter for many species.

“This shows that we can learn from nature’s design strategies to enhance man-made green walls,” said Hecht. “They provide valuable habitats in places that would otherwise be inhospitable for many species.”

Role of surrounding greenery

Hecht noted that plant-covered walls alone cannot maximize their ecological potential. The surrounding environment plays a crucial role in their effectiveness.

“What I found really interesting to confirm in our study is how important trees and other vegetation are,” she said.

“The crowns of nearby trees and patches of greenery serve as stepping stones. They allow bees, bugs, and even small birds to hop from tree to tree, and eventually reach the green walls.”

Without a network of trees and vegetation, green walls may struggle to attract diverse species. Isolated green walls offer limited benefits compared to those integrated into larger green corridors. Urban planners and architects must consider the broader ecological landscape when designing green spaces.

Applications beyond the tropics

Although the study focused on Singapore’s tropical climate, Hecht believes the findings apply to temperate regions as well. She noted that the principles of green wall design remain consistent across different climates.

“The principles would be similar,” said Hecht. “Although we would need to tailor the plant species and specific designs to the local biodiversity and weather conditions.”

In temperate regions, green walls may naturally be colonized by mosses, perennials, and local climbers. These plants could influence the types of species that thrive. Architects and ecologists must adapt their designs to match local climate conditions while preserving the ecological benefits of green walls.

Expanding research on green walls

The study highlights the need for more research on green walls, particularly in temperate regions.

Earlier studies in the Netherlands, conducted by students from Utrecht University, have shown promising results. However, Hecht emphasizes that more empirical data is necessary to confirm the long-term benefits of green walls in different climates.

She is already leading a follow-up project under Utrecht University’s “Pathways to Sustainability” program. Her team is developing a digital system to collect and compare data on green walls from different locations.

By analyzing data from multiple climates, the researchers aim to refine plant-covered wall designs and maximize their ecological potential.

Building a greener future

The foundation of this research was laid by Leanne Haan, a master’s student at Utrecht University. She conducted the initial fieldwork in Singapore, spending eight months collecting data.

Her work included trekking through urban parks to gather information that helped launch the research project.

Haan’s efforts not only provided critical data but also established strong collaboration between Utrecht University and Singapore-based researchers. The success of this study highlights the importance of interdisciplinary research in creating sustainable urban solutions.

As cities continue to grow, integrating green walls into urban planning could help mitigate climate change, reduce heat, and support biodiversity. With more research and innovation, these living facades could become a standard feature in the cities of the future.

The study is published in the journal Building and Environment.

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