What are the most efficient cooling interventions for urban heat globally?

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Globally, botanical gardens, wetlands, green walls, street trees, and vegetated balconies offer the most effective air cooling in urban environments.

A comprehensive global review of green and blue-grey infrastructure (GBGI) reveals significant variations in urban cooling effectiveness across different regions and specific interventions. These infrastructures mitigate urban heat through processes like evaporation, transpiration, shading, and thermal insulation. While green elements like trees and grass provide cooling, blue infrastructures, such as water bodies, also contribute by absorbing heat and cooling the surrounding areas through evaporation.
Regional Cooling Effects of Green and Blue-Grey Infrastructure

The overall cooling impact of GBGI varies considerably by continent. In Europe, the cooling effect can be as high as 18.9°C, while in Asia, it reaches up to 17.7°C. North America observes a cooling effect of up to 12°C, and Australia records a maximum of 9.63°C. These figures highlight the diverse potential of these interventions depending on local conditions and the types of infrastructure implemented.
Asian Cities' Most Effective Cooling Strategies

Within Asian cities, engineered grey infrastructures, particularly roof gardens and pergolas, have demonstrated the highest efficacy in reducing urban temperatures. Singapore's roof gardens, for instance, achieved a notable temperature reduction of 17.7°C. In Japan and South Korea, pergolas and green roofs contributed to cooling by 16.2°C and 10.8°C respectively. Additionally, linear hedges and street trees have shown considerable impact, lowering temperatures by up to 10.8°C.
Specific Interventions in Mainland China and Hong Kong

In cities across Mainland China, botanical gardens, wetlands, green walls, and attenuation ponds have shown significant cooling effects, reducing temperatures by up to 10°C, 9.27°C, 8°C, and 7°C, respectively. For example, botanical gardens in Beijing can lead to a 10°C decrease. In Hong Kong, parks and green roofs are instrumental in mitigating urban heat, each providing a temperature reduction of 4.9°C, with golf courses contributing a 4.2°C reduction.
Framework for Implementing Green and Blue-Grey Infrastructure

To guide the effective implementation of GBGI, a nine-stage framework has been introduced. This framework encompasses stages from stakeholder engagement and feasibility studies through to design, policy development, implementation, monitoring, evaluation, and finally, upscaling and replication. This structured approach aims to optimise the benefits of GBGI and support the development of sustainable and resilient cities.

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What are the most efficient cooling interventions for urban heat globally?

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