Urban densification and green space trade-offs for climate regulation in Sydney, Australia

Background/Question/Methods

In many parts of the world, urbanization is rapidly changing city landscapes, leading to reduced space for urban ecosystems. However, urban green spaces can provide many ecosystem services for cities, including climate regulation services that help reduce extreme temperatures during heat waves. Thus, the loss of urban ecosystems means a loss of many beneficial services for urban citizens. Because of this, there is growing tension to build more compact, dense urban areas while providing urban green spaces for ecosystem services and climate adaption. In this study, we investigate the spatial distribution of green space within Sydney, Australia, to determine how patterns of green space vary according to land use and residential density and how these patterns affect the ability to deliver the ecosystem service of climate regulation. Using hyperspectral and thermal airborne remote sensing imagery, we quantify the effect of tree shade on surface temperatures at the neighbourhood scale, and we explore the trade-offs between public and private green space availability in providing climate regulation services.

Results/Conclusions

More than half of urban Sydney is comprised of residential land use (private green space), representing the single largest contribution to Sydney’s green infrastructure. However, results show that as suburb dwelling density increases, the residential tree canopy cover decreases, and this loss of residential tree canopy is not compensated for by an increase in the area of suburban parkland (public green space). This reveals a general trend in green space reduction with increasing urbanization. At the neighbourhood scale, it was found that tree canopy cover reduces the surface temperatures of house rooftops and roads; and within neighbourhood parks, as tree cover increases, the land surface temperature decreases, showing that denser shade confers greater temperature reduction benefits. Thus, the loss of tree cover and green space in neighborhoods has also led to a greater exposure to high temperatures for people who live in these areas. Collectively, these findings highlight the shared responsibility of both public and private space for providing green space and the climate regulation services from such land uses, and the continued loss of urban green space from cities presents a challenge to urban decision-makers faced with urban heat waves.