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.
•Background and Timeline to the Urban Heat Island (UHI) is provided.•Key causes and consequences of the UHI are outlined and analysed.•Asphalt concrete's thermal properties are shown to significantly affect the UHI.•Existing mitigation measures discussed, and future methods outlined.•Combining different mitigation methods is an effective strategy against the UHI.
Urban heat island (UHI) could have significant impacts on building energy consumption by increasing space cooling demand and decreasing space heating demand. However, the impacts of UHI on building ...energy consumption were understudied due to challenges associated with quantifying UHI-induced temperature change and evaluating building energy consumption. In this study, we reviewed existing literature for improving the understanding of UHI impacts on building energy consumption. It was found that UHI could result in a median increase of 19.0% in cooling energy consumption and a median decrease of 18.7% in heating energy consumption. The reported UHI impacts showed strong intercity variations with an increase of cooling energy consumption from 10% to 120% and a decrease of heating energy consumption from 3% to 45%. The UHI impacts also showed clear intra-city variations with stronger impacts in urban center than that in urban periphery. There were significant differences in the method and the data used to evaluate the UHI impacts in previous studies. Four future research focuses were recommended to better understand the UHI impacts on building energy consumption.
•The literature of UHI impacts on building energy consumption was reviewed.•UHI could lead to a median of 19% increase in building cooling energy consumption.•UHI could lead to a median of 18.7% decrease in building heating energy consumption.•UHI impacts showed strong spatial variations within and among cities.•Four future research focuses were recommended for better understanding of UHI impacts.
The combination of global warming and urban sprawl is the origin of the most hazardous climate change effect detected at urban level: Urban Heat Island, representing the urban overheating respect to ...the countryside surrounding the city. This book includes 18 papers representing the state of the art of detection, assessment mitigation and adaption to urban overheating. Advanced methods, strategies and technologies are here analyzed including relevant issues as: the role of urban materials and fabrics on urban climate and their potential mitigation, the impact of greenery and vegetation to reduce urban temperatures and improve the thermal comfort, the role the urban geometry in the air temperature rise, the use of satellite and ground data to assess and quantify the urban overheating and develop mitigation solutions, calculation methods and application to predict and assess mitigation scenarios. The outcomes of the book are thus relevant for a wide multidisciplinary audience, including: environmental scientists and engineers, architect and urban planners, policy makers and students.
•The urban heat island expansion index was developed to identify the new UHI patches.•The new UHI patches are reclassified as infilling, edge-expanding and leapfrogging.•The new UHI patches have ...lower UHII but higher contributions than pre-existing patches.•The new UHI patches are predominantly edge-expanding with the maximum UHII.•Croplands, rural residential areas, and forests were the main sources for new UHI patches.
Urban ecological resilience enhancement is important for the mitigation of climate change risks; however, urban heat islands (UHIs) have negative impacts on urban resilience. A UHI expansion index (UHIEI) was developed to identify new UHI patches produced by including infilling, edge expansion, and leapfrogging. In this study, we used a simplified urban extent (SUE) algorithm to estimate new UHI patches and their associated UHI intensity (UHII) values in 371 cities in China during 2005–2020. Then, we analyzed the sources and sinks of the UHI patches according to land use data. The study sought to comprehensively determine the spatial expansion path of the new UHI patches at the national scale. The results showed mean UHII values of 2.11 °C ± 0.63 °C and 1.06 °C ± 0.54 °C during the day and night, respectively, for the 371 cities in the summer of 2020; these were slightly higher than the corresponding values in 2005. The UHII values of the new UHI patches were 0.57 °C and 0.29 °C lower during the day and night, respectively, compared with pre-existing UHI patches in summer. New UHI patches were predominantly formed through edge expansion, with maximum UHII values of 1.74 °C ± 0.80 °C and 0.88 °C ± 0.42 °C during the day and night, respectively; these are lower than the values of pre-existing UHI patches, but they represent greater contributions to the land surface temperature (LST) of the city. Croplands, rural residential areas, and forests were the main sources for new UHI patches. The results of this study will allow better identification and comparison of the temporal and spatial characteristics of pre-existing and new UHI patches; they will also facilitate the design of targeted measures to mitigate their ecological impacts according to expansion type, thereby improving the cities’ ecological resilience characteristics.
•The current status of UHI mitigation studies in Toronto are reviewed.•Three locations in Toronto are selected for the environmental simulation.•The effects of cool pavement, cool roof and urban ...vegetation on UHI are discussed.•UHI mitigation strategies are simulated and discussed in both summer and winter.•The results support new policies for sustainable urban development in Toronto.
Increasing awareness of the urban heat island (UHI) effect has raised attention about the outdoor thermal comfort in cities worldwide. Several studies in the last decades have revealed how critical the UHI effect can be in a cold climate, such as in Canadian cities. As a result, in Toronto, one of the cities experiencing the highest rate of building development in developed countries, UHI mitigation strategies are currently the object of extensive debates. This study evaluates different UHI mitigation strategies in different urban neighbors of Toronto, selected according to their building density. The effects of cool surfaces (on the roofs, on the street pavements or as vegetation areas) are evaluated through numerical simulations using the software ENVI-met. Having obtained the surface temperature, outdoor air temperature, mean radiant temperature, and physiologically equivalent temperature, this study compares the possible mitigation of net surface radiation and thermal radiative power. The results demonstrate that the duration of direct sun and the mean radiant temperature, which are strongly influenced by the urban form, play a significant role in urban thermal comfort. Finally, this research supports new policies for promoting sustainable urban development in Toronto, and suggests design strategies for a more resilient urban planning.
•Morphology-based tree planning methods are evaluated by measurement and simulation.•Cooling on road surface is 18°C and 15°C under high and low SVF, respectively.•Comfortable Tmrt (34°C) is provided ...by trees in heavily built areas with low SVF.•Combining trees with wind path doubles cooling in temperature and sensible heat.
Hong Kong suffers from an intense urban heat island (UHI) effect of up to 4°C as a result of compact urban form and highly urbanized land cover. Enhancing the cooling efficiency of urban greenery is essential for improving the microclimate in high-density cities. This paper aims to delineate design strategies for urban greenery to maximize thermal benefits and mitigate the daytime UHI effect. Two site-specific design strategies for tree planting in the urban environment are proposed. The sky view factor (SVF)-based design approach and the wind-path design approach are evaluated in the neighbourhood scale in two climate-sensitive areas with different urban morphologies. Observed data and simulation results indicated that the cooling effect of urban trees is highly associated with SVF. Air temperature reduction (a 1.5°C reduction) is the most profound for the high SVF scenario, whereas substantial radiation shading (Tmrt reduced to 34°C) is detected in areas with medium-low SVFs. The modelling study also showed that the cooling of air temperature and sensible heat were twice as high for vegetation arranged in wind corridors than those for leeward areas. The study demonstrated that tree planting in conjunction with proper planning is an effective measure to mitigate daytime UHI.
Due to its importance, the field of urban heat islands (UHIs) has witnessed an increasing trend of interest over time to many scientists on the international level. Consequently, large number of ...papers has been published aiming at reviewing the literature about UHIs internationally. However, this topic started to attract attention of researchers in the Arab world only relatively recently. Hence, the major goal of the present endeavor is to narratively review the literature about UHIs in the Arab world. The focus is on two significant aspects of UHIs: (1) determination of UHIs and (2) assessment of the impacts of UHIs. The results of this review exposed to the surface the historical development, current status, and future prospects of literature about determination and assessment of the impacts of UHIs in the Arab world. The research about this specific topic in the Arab world can be described as still in its infancy stage with huge gaps still exist and more further studies are needed.
Urban heat island is the more documented phenomenon of climate change. Information on the magnitude and the characteristics of the canopy layer urban heat island measured in 101 cities and regions of ...Asia and Australia and collected through 88 scientific articles, are compiled, evaluated and presented. Data are classified in several clusters according to the experimental protocol used and the type of statistical information reported regarding the magnitude of the urban heat island. Results and detailed analysis are given for each defined cluster. Very significant differences on the UHI intensity are found between the clusters and analyzed in detail. The detailed impact of the main weather parameters and conditions on the magnitude of the UHI is also investigated. The specific influence of anthropogenic thermal fluxes as well as of the urban morphological and construction characteristics to UHI is thoroughly examined. The relation between the UHI intensity and the city size is assessed and global relationships of UHI as a function of the urban population are proposed. The seasonal and diurnal variability of the UHI is analyzed and discussed while specific features and conditions like the urban heat island characteristics in coastal cities and the existence of daytime cool islands are explored. Finally, the impact of the selected reference station and its characteristics is considered.
This reprint focuses on the theoretical principles and practical adoption of remote sensing approaches and datasets in understanding the nexus between urbanization, natural landscapes, urban ...micro-climate, climate change and Urban Heat Islands. Urbanization, characterized by natural landscape transformation, influences thermodynamics, surface energy and micro- and macro climate perturbations. These changes result in environmental deterioration that in turn adversely affects bio-physical processes and quality of urban life. A major consequence of urbanization is the Urban Heat Island (UHI). It is anticipated that the increased UHIs, in concert with the increasing anthropogenic activities, will further increase the vulnerability of urban landscapes to climate-related disasters such as floods and heatwaves. Recent advances in optical and thermal remotely sensed datasets offer great potential in understanding the relationship between urban bio-physical characteristics and UHIs. Hence, this reprint provides a basis for understanding urban ecological and thermal patterns, which is critical for the management of urban physical, ecological and social processes within a remotely sensed data framework. This reprint should be of interest to both specialists and generalists interested in, among other fields, urban planning, ecological conservation, the urban micro-climate, and climate change.
This Special Issue explores the fascinating topic of urban heat islands (UHIs), examining them from temporal and spatial perspectives. We embark on a journey that focuses on the essential impacts of ...UHI formations, including land use composition, city characteristics, and anthropogenic factors. Our objective is to raise awareness of the many facets of UHIs and their significant effects on urban environments and sustainability. This collective aim is to further strengthen urban sustainability through a deeper understanding of UHI dynamics. This volume includes a wide range of topics related to UHIs, including cutting-edge methods and datasets for capturing UHI phenomena. We investigate the spatial interactions between UHI intensity and land use/cover distribution within metropolitan areas, examine the geographic patterns and processes underlying UHIs in sprawling cities, and analyze the spatial differences in UHI intensity between developing and developed countries. Additionally, we focus on UHI catastrophe mitigation and adaptation measures, which are crucial for setting sail for a sustainable urban future. Finally, we engage in the critical work of prediction and scenario analysis, equipping policymakers and urban planners with the insights necessary for informed decision-making. We express our thanks to the researchers, academics, and contributors who have made this Special Issue possible as we begin this investigation into urban heat islands. We aim to foster a comprehensive understanding of UHIs and contribute to the broader discourse on urban sustainability.
