Multi-scale analysis of the surface layer urban heat island effect in five higher density precincts of central Sydney

Abstract

The urban heat island (UHI) effect is invariably present in cities, mainly due to increased urbanisation. It can result in higher urban densities being significantly hotter (frequently more than 4°C, even up to 10°C) than their peri-urban surroundings. Urban structure and land cover are key contributors to the surface layer urban heat island (sUHI) effect at city and district scale. This research aims to explore which urban configurations can make urban precincts and their microclimates more resilient to the dangerous sUHI effect. In the context of the city of Sydney, Australia, the research aims to explore the most heat resilient urban features for neighbourhoods, at precinct scale. The investigation examines five high density precincts in central Sydney. The analysis of these precincts is based on remote sensing thermal data of two independent sources: a nocturnal remote-sensing thermal image of central Sydney on 6 February 2009 and a diurnal Landsat 7– ETM+ data from 2008-2009. Comparing the surface temperature of streetscape and buildings’ rooftop feature layers indicates that open spaces are the urban elements most sensitive to the sUHI effect. Therefore, the correlations between street network intensity, open public space ratio, and urban greenery plot ratio and sUHI effect are being analysed in the five high density precincts selected. Results indicate that a higher open space ratio and street network intensity have a significant correlation to a higher sUHI effect at precinct scale. However, higher urban greenery plot ratios could mitigate the sUHI effect in these precincts. In addition, annual variation of land use features of streetscape, building (rooftop), open space and urban greenery are being analysed based on diurnal Landsat 7– ETM+ data for 2008-2009. Results indicate that an increase in urban greenery is the most effective strategy for land surface that is more resilient to the sUHI, while open public space is up to 15 per cent less heat resilient. The research outcomes support the importance of increasing urban greenery, particularly in open public spaces, to achieve cooler cities.