Academic journal article Journal of Sustainable Development

Comparative Analysis of Surface Urban Heat Island Effect in Central Sydney

Academic journal article Journal of Sustainable Development

Comparative Analysis of Surface Urban Heat Island Effect in Central Sydney

Article excerpt

Abstract

The Urban Heat Island (UHI) effect can result in higher urban densities being significantly hotter (frequently more than 4 °C, even up to 10 °C) compared to their peri-urban surroundings. Such artificial heat stress increases the health risk of spending time outdoors and boosts the need for energy consumption, particularly for cooling during summer. Urban structure, land cover and metabolism are underlined as key contributors in city scale. Under question is which urban configurations can make urban precincts and their microclimates more resilient to the surface layer Urban Heat Island (sUHI) effect?

The City of Sydney is increasingly experiencing the UHI effect due to its numerous urban development projects and changes in climate. In the Sydney context, this ongoing research aims to explore the most heat resilient urban features at precinct scale. It covers five high density precincts in central Sydney and is based on a nocturnal remote-sensing thermal image of central Sydney taken on 6 February 2009. Comparing the surface temperature of streetscapes and buildings' rooftops (dominant urban horizontal surfaces), indicates that open public spaces and particularly streetscapes are the most sensitive urban elements to the sUHI effect. The correlations between street network intensity, open public space plot ratio, urban greenery plot ratio and sUHI effect is being analysed in Sydney's high density precincts. Results indicate that higher open space plot ratio and street network intensity correlate significantly to higher sUHI effect at precinct scale. However, higher urban greenery plot ratio can effectively mitigate the sUHI effect in high density precincts.

Keywords: urban heat island effect, urban greenery, public space surface, streetscape, heat stress, Sydney

1. Introduction

Cities are anticipated to accommodate up to 70% of the global population by 2050 (DESA, 2012). Compared to the current urbanization rate of 50%, almost all the expected global population growth will be accommodated in cities. Such rapid urbanization means higher densities in existing cities and many more new urban areas to accommodate up to 2 billion new urban dwellers. However, rapid urban development in fast-growing cities tends to overlook the environmental and social aspects of urban life (Girardet, 2008; Lehmann, 2010; Register, 2002). A considerable amount of natural landscape is transformed into building mass and hard surfaces, creating environmental threats for existing and future cities.

With huge demands for natural resources (i.e. energy, food, water and materials) cities are contributing up to 80% of greenhouse gas (GhG) emissions, resulting in global warming (UNECE, 2011; UNHS, 2011). Climate change projections indicate a likely increase of 2 to 5 °C in Australian surface temperature by 2050 (CSIRO, 2007; OECD, 2010). Such an increase in temperature will have a severe impact on natural ecosystems and human life in cities, including public health and quality of public space (Guest et al., 1999; Stone, 2012).

Cities also suffer from the effect of an additional form of heat, known as the Urban Heat Island (UHI) effect. This human-made heat is trapped in the built environment's thermal mass and can result in higher densities being significantly hotter, compared to their peri-urban surroundings. The urban-rural temperature difference frequently reaches 4.0 °C and can peak at more than 10 °C (Gartland, 2008; Oke, 2006; Wong & Yu, 2008). Such additional heat can seriously impact citizens' health and the quality of public life in cities.

The higher density of cities can bring efficiency gains, but there is interplay between the increased risk of the urban heat island effect and higher densities, which needs to be understood. Because cities are often covered in heat-absorbing surfaces and materials, such as concrete and bitumen, they absorb and store heat (e.g. through solar radiation), making urban areas warmer than the surrounding hinterland and rural areas, especially at night time. …

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