SIMULATING COOLING STREET STRATEGIES ON URBAN HEAT ISLANDS EFFECTS: AN EMPIRICAL STUDY FOR BLACKTOWN CITY, AUSTRALIA

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ABSTRACT

Australia has ranked as one of the most vulnerable countries to the effects of climate change. The rising trend of temperature is intensifying the creation and extension of urban heat islands (UHI). This paper investigates different cooling street strategies in line with developing resilient Sydney to the effects of climate change. Two different approaches are investigated including, green canopy and cool pavement. A wide range of impacted parameters is examined including Air Temperature, Surface Temperature, Sensible Heat Flux, Sky View Factor, Human Thermal Comfort, and Mean Radiant Temperature. Also, different surface reactions to the sun and shadow were surveyed to investigate the various materials responses to the different levels of shadow. ENVImet software is adopted to simulate and quantify microclimate processes before and after introducing cooling street strategies. This study demonstrates that replacing asphalt pavement with light concrete pavement reduces surface temperature by up to 20°C. Planting short to medium height trees reduces air temperature by up to 3°C and surface temperature by up to 11°C. Also, human thermal comfort has a direct relationship with the Sky View Factor at daytime. Besides, the study proves that the Mean Radiant Temperature is reduced considerably by both green canopy and light pavement scenarios in the daytime; however, the night time radiant heat does not differ substantially in any of the scenarios. Overall, both proposed initiatives show the positive cooling effects on air, surface, and mean radiant temperature, human thermal comfort, and the heat fluxes in the daytime; however, the cool pavement scenario decreases both daytime and night-time air and surface temperature.

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The energetic basis of the urban heat island

T. Oke (1982)

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The urban heat island effect, its causes, and mitigation, with reference to the thermal properties of asphalt concrete.

Abbas Mohajerani, Jason Bakaric, Tristan Jeffrey-Bailey (2017)

The Urban Heat Island (UHI) is a phenomenon that affects many millions of people worldwide. The higher temperatures experienced in urban areas compared to the surrounding countryside has enormous consequences for the health and wellbeing of people living in cities. The increased use of manmade materials and increased anthropogenic heat production are the main causes of the UHI. This has led to the understanding that increased urbanisation is the primary cause of the urban heat island. The UHI effect also leads to increased energy needs that further contribute to the heating of our urban landscape, and the associated environmental and public health consequences. Pavements and roofs dominate the urban surface exposed to solar irradiation. This review article outlines the contribution that pavements make to the UHI effect and analyses localized and citywide mitigation strategies against the UHI. Asphalt Concrete (AC) is one of the most common pavement surfacing materials and is a significant contributor to the UHI. Densely graded AC has low albedo and high volumetric heat capacity, which results in surface temperatures reaching upwards of 60 °C on hot summer days. Cooling the surface of a pavement by utilizing cool pavements has been a consistent theme in recent literature. Cool pavements can be reflective or evaporative. However, the urban geometry and local atmospheric conditions should dictate whether or not these mitigation strategies should be used. Otherwise both of these pavements can actually increase the UHI effect. Increasing the prevalence of green spaces through the installation of street trees, city parks and rooftop gardens has consistently demonstrated a reduction in the UHI effect. Green spaces also increase the cooling effect derived from water and wind sources. This literature review demonstrates that UHI mitigation techniques are best used in combination with each other. As a result of the study, it was concluded that the current mitigation measures need development to make them relevant to various climates and throughout the year. There are also many possible sources of future study, and alternative measures for mitigation have been described, thereby providing scope for future research and development following this review.