Effectiveness of Road Cool Pavements, Greenery, and Canopies to Reduce the Urban Heat Island Effects

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Abstract

The ongoing climate change is manifesting itself through the increasing expansion of Urban Heat Island (UHI) effects. This paper evaluates the microclimate benefits due to cool road pavements, greenery, and photovoltaic canopies in a parking lot in Fondi (Italy), identifying the best strategy to counteract the negative effects of UHIs. The ENVI-met software allowed a microclimatic analysis of the examined area in July 2022 through the comparison of the thermal performances between the current asphalt pavement and ten alternative scenarios. The proposed layouts were investigated in terms of air temperature (AT), surface temperature (ST), mean radiant temperature (MRT), and predicted mean vote (PMV). The results showed that the existing asphalt pavement is the worst one, while the cool pavement integrated with vegetation provides appreciable benefits. Compared to the current layout, a new scenario characterized by light porous concrete for carriageable pavements and sidewalks, concrete grass grid pavers for parking stalls, a 2-m-high border hedge, and 15-m-high trees implies reductions of AT above 3 °C, ST above 30 °C, MRT above 20 °C, and a maximum PMV value equal to 2.2.

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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.