Green-blue-grey infrastructure effective in mitigating urban heat: study

A framework was introduced to guide GBGI implementation.

The Hong Kong Polytechnic University (PolyU) along with global researchers discovered that green-blue-grey infrastructure (GBGI) was an effective way to address the increasing heat being experienced in urban areas like Hong Kong.

According to PolyU, GBGI refers to green infrastructures that encompass naturally vegetation-based elements like trees, grass and hedges; blue infrastructures are water-based features like pools, lakes and rivers; and grey infrastructures are engineered structures including green walls, green facades and roofs.

Hai Guo, professor from the Department of Civil and Environmental Engineering at PolyU, joined the team of researchers to look into the effectiveness of GBGI in air cooling. 

The study found that GBGI was indeed effective and results vary depending on the area.

Specifically in Hong Kong, parks, green roofs and golf courses played vital roles in cooling urban heat, resulting in temperature reductions of 4.9°C, 4.9°C, and 4.2°C, respectively.

“Whilst green infrastructures can regulate urban heat through evaporation, transpiration, shading and thermal insulation, blue infrastructures absorb heat and cool the surrounding area through evaporation,” the study said. 

To help countries implement and maximise the benefits of GBGI, the researchers introduced a nine-stage framework. This outlines stages of stakeholder engagement, feasibility studies, design, policy development, implementation, monitoring, evaluation, eventual upscaling, and replication.

“Policymakers should conduct thorough investigation and planning tailored to the specific context and needs of their cities,” Guo said. “It is crucial for future GBGI implementation to adopt a holistic approach, optimising their multifunctional benefits to effectively address sustainability goals."

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Guo noted that the Hong Kong government actively promotes GBGI in new development areas and the adoption of green building design in new public projects. 

The “Shining City Project” to enhance urban green spaces was also proposed last year. This will involve greening of riverbanks, and planting of more trees in government venues and along major roads.