Urban heat mitigation by green and blue infrastructure: Drivers, effectiveness, and future needs

This systematic review synthesizes evidence from 202 peer-reviewed studies to evaluate the effectiveness of 51 types of green-blue-grey infrastructure (GBGI) in mitigating urban heat. As urbanization and climate change intensify heatwaves, understanding which interventions—ranging from parks and wetlands to green walls and roofs—provide the most reliable cooling is essential for urban planning. The authors categorized these interventions into 10 divisions and analyzed their performance across different climate zones, spatial scales, and methodologies.

The study identifies botanical gardens, wetlands, green walls, and street trees as the top-performing GBGI types for reducing air temperatures. While micro-scale interventions like green walls and street trees are highly effective for immediate, localized cooling, the research highlights that their efficiency is highly dependent on local climatic conditions, population density, and the surrounding urban environment. A notable finding is the potential for future climate shifts to reduce the efficacy of current GBGI strategies, suggesting that urban planners must look beyond present-day performance and consider long-term climate projections (e.g., RCP8.5) when designing resilient cities.

As cities densify, the urban heat island effect poses a direct threat to public health, energy consumption, and economic stability. This paper provides a comprehensive inventory that helps policymakers prioritize interventions based on evidence rather than intuition. By highlighting the multifunctional nature of GBGI—which can provide co-benefits like biodiversity and stormwater management alongside cooling—the authors offer a framework for creating more sustainable and climate-resilient urban landscapes. The study also serves as a call to action for researchers to address significant knowledge gaps, particularly regarding under-researched GBGI types and the need for standardized monitoring protocols.