Article published in the UNDRR Prevention Web. UNDRR is a United Nations Agency, for the coordination of disaster risk reduction.
A study published in The Innovation in March 2024 reviews thousands of papers on green-blue-grey infrastructure (GBGI), such as parks, wetlands, and engineered greening, focusing on their effectiveness in mitigating urban heating and their co-benefits.
Researchers screened 27,486 papers and reviewed 202 based on 51 types of green-blue-grey infrastructure (GBGI) classified under ten broad categories for their cooling benefits. They found that botanical gardens, wetlands, green walls, street trees, and vegetated balconies offered the most efficient air cooling.
A systematic review of hundreds of studies on green infrastructure shows that it regulates urban heating and reduces temperatures through shading, evapotranspiration, and thermal insulation. The cooling associated with green and blue infrastructure is also linked to lower energy consumption in buildings.
Examining where these studies are conducted and the type of GBGI being studied shows that most of the studies of green infrastructure originate from Asia (51.1%), primarily from China (29.95%), followed by Europe (30.4%), Australia (7.5%), and North America (7.0%).
Far fewer studies have been carried out in South America (1.8%), Africa (1.8%), and New Zealand (0.4%)
The type of GBGI studied also varied across continents.
Wetlands (14.7%) and parks (12.9%) were the most frequently studied GBGI types for combating urban overheating in Asia. In contrast, the most common GBGI measures reported in Europe were street trees (18.8%), green walls (15.9%), and green roofs (13.0%).
In Australia, green wall studies were prominent (17.6%), alongside irrigating backyards, parks, street trees, and green roofs, making up (58.8%) of the total GBGI studies. In North America, parks (31.3%), street trees (18.8%), and wetlands (12.5%) made up approximately (62.5%) of GBGI interventions described.
According to the study, the differences in the types of GBGI studied across continents likely stem from diverse regional contexts, climate conditions, and urban planning priorities reflecting the varying environmental needs and urban challenges specific to each continent and the best GBGI interventions to tackle urban overheating in their respective regions.
Besides cooling, GBGI’s co-benefits include managing stormwater, reducing flooding and sequestering CO2. However, potential drawbacks can consist of increased maintenance costs and land-use conflicts. Street trees offer the highest co-benefits in cooling and climate adaptation, followed by green roofs and botanical gardens.
In contrast, Playgrounds, green walls, green roofs, and street trees had the highest reported drawbacks, such as pollutants trapped in street canyons and allergic rhinitis. The study highlights the importance of considering a balanced heat mitigation and adaptation approach during their implementation.
The study provides a heat mitigation inventory that could help policymakers and urban planners select the best GBGI approach to reduce heatwaves and lower temperatures in cities facing the rising risks of extreme and deadly heatwaves that are projected to increase in intensity and frequency due to climate change.