|Siti Halipah Ibrahim||Department of Civil Engineering, Faculty of Engineering, Universiti Malaysia Sarawak (UNIMAS), Jalan Datuk Mohammad Musa, 94300 Kota Samarahan, Sarawak|
|Nurul Izzati Ahmat Ibrahim||Department of Civil Engineering, Faculty of Engineering, Universiti Malaysia Sarawak (UNIMAS), Jalan Datuk Mohammad Musa, 94300 Kota Samarahan, Sarawak|
|Julaihi Wahid||Department of Civil Engineering, Faculty of Engineering, Universiti Malaysia Sarawak (UNIMAS), Jalan Datuk Mohammad Musa, 94300 Kota Samarahan, Sarawak|
|Nurakmal Abdullah Goh|
|Dona Rose Amer Koesmeri|
|Mohd Nasrun Mohd Nawi||School of Technology Management and Logistic, Universiti Utara Malaysia, 06010 Sintok, Kedah, Malaysia|
An urban heat island (UHI) is a climatic phenomenon caused by modifications to the climate due to changes in the form and composition of the land surface and atmosphere. The aim of this study is to investigate the impact of road pavement types for mitigating or intensifying UHI. This study was conducted in the Kota Samarahan area. Since Kota Samarahan is classified as a suburban area, it is still a developing district. Hence, there is still an opportunity for proper planning, such as choosing the most suitable type of pavement, before this area becomes a UHI. Data was collected by studying four types of pavements (asphalt, concrete, permeable, and industrialised building system (IBS) StormPav) in terms of their characteristics, performance, and maintenance costs. Additionally, their surface temperatures were investigated using ThermaCam and then plotted against the surrounding air temperature. Interview sessions were also conducted with the personnel of Jabatan Kerja Raya to obtain valuable information for this research. As a result, this study found that the construction of asphalt pavement can produce numerous potential impacts on the environment, which further contribute to air pollution and the UHI effect. Concrete, permeable, and IBS StormPav pavements retained less heat compared to asphalt, and can be implement to mitigate the UHI phenomenon. Furthermore, the implementation of green walls, cool roofs, vegetation and trees, and altering the properties and construction of asphalt pavement can help in mitigating this phenomenon.
Air temperature; Pavement; Surface temperature; Urban heat island (UHI)
The phenomenon known as an urban heat island (UHI) often forms in urban and suburban areas where the surface temperature and air are hotter than the rural surroundings. A heat island is also known as a reverse oasis. This phenomenon has been found in many cities worldwide and is growing. In 1818, Luke Howard’s study of London’s climate was the first documented UHI (Gartland, 2012). He found that the city had artificial heat in comparison to the country. Similar discoveries were made by Emilien Renou about Paris during the second half of the 19th century.
This phenomenon is seen as a negative factor in thermal comfort. The UHI phenomenon is simply the storage of solar energy during daytime (Katzschner, 2009), which would normally be released into the atmosphere at night. Heat islands are common in urban and suburban areas due to the concentrations of structures and pavement. The structures are typically composed of materials such as concrete that can retain and absorb higher amounts of heat from the sun than the natural materials utilized in rural areas (Gartland, 2012). Furthermore, the dark materials in concert with canyon-like configurations of pavement and buildings further contribute to the absorption of heat. When vegetated surfaces with moist soil underneath are exposed to direct sunlight, the temperature of the heat absorbed is only around 18°C (Gartland, 2012). However, the temperatures absorbed by dark and dry surfaces exposed to the same conditions can reach up to 52°C (Ibrahim et al., 2014). Waste heat from human activity also exacerbates this phenomenon. Some of the most notable sources of waste heat are air conditioners and emissions from vehicle engines.
The paved surfaces in urban and suburban areas are often warmer than the less-paved surfaces in rural areas. Pavement is usually comprised of materials with very low reflectivity or albedo. Albedo is defined as the fraction of the incident radiation that is reflected from a surface (Dobos, 2003). It plays a significant role in the energy balance on the surface of the earth since it defines how much solar radiation is absorbed.
Surfaces generally absorb most of the radiation that comes into contact with them (Calkins, 2012). This heats up the pavement material and the heat is then reradiated, elevating the surrounding ambient air temperatures. In pavement structures, the only surface which affects albedo is the topmost layer. Hence, if heat generation is a concern, albedo should be taken into consideration when selecting a pavement type. The two most commonly used pavements worldwide are hot mix asphalt (HMA) and Portland cement concrete (PCC) pavements. Permeable pavement is also commonly used in urban areas, usually in sidewalks and parking lots.
Figure 1 UHI profile (Katzschner, 2009)
Not only does the UHI increase the daytime temperature and reduce nighttime cooling, it is also associated with air pollution. This phenomenon leads to increased energy demand for air conditioning, which releases more heat as well as greenhouse gas emissions into the air (Rosenfeld et al., 1995). Therefore, the local air quality is degraded. Additionally, human health can also be affected by air pollution, leading to respiratory difficulties, heat cramps, non-fatal heat stroke, and general discomfort (Li, 2015). Sensitive populations such as older adults and children have the highest risk for these negative health effects.
In comparison to the rural surrounding areas, the urban areas have higher temperatures. The man-made land formed by development activities in an urban area can increase the environmental temperature by 0.5–1.5? (Brontowiyono et al., 2011). The modification of land surfaces using materials such as asphalt and concrete are considered to be the main factors that influence the environmental temperature and surface energy balance in urban areas. Generally, pavements have relatively high solar energy absorption because they possess a higher heat storage capacity. They tend to absorb heat during the day and then slowly release it back into the atmosphere at night (Katzschner, 2009).
Figure 2 Daily temperature of a Phoenix street (American Concrete Pavement Association, 2009)
Numerous theoretical and experimental studies have suggested that paved surfaces play a significant role in increased urban temperatures and declining ambient quality. A case study conducted by Rose et al. (2003) in Greater Houston, Texas concluded that 29% of the cities in that area are covered by paved surfaces. Another study conducted in metropolitan Chicago, Illinois by Akbari and Rose (2001) indicated that sidewalks, roads, and parking areas cover about 29–39% of the city when viewed from above the urban canopy and 36–45% when viewed from below the urban canopy. Various experimental studies conducted worldwide have also concluded that one of the main contributors to the UHI phenomenon is pavement (e.g., Asaeda et al., 1996). Therefore, it is crucial to study the pavement types and characteristics and how these contribute to the intensification or mitigation of this phenomenon.
In conclusion, since Malaysia is experiencing rapid urbanization, it is extremely important that the issue of UHI be addressed before the country experiences levels similar to Tokyo, Thailand, Paris, and other cities. Some strategies have been outlined to mitigate the UHI phenomenon:
• Implementation of green walls
• Implementation of cool/green roofs
• Minimizing the environmental impact of asphalt pavement
• Planting trees and vegetation
• Implementation of permeable pavement or surfaces
• Implementation of cool pavement
One of limitations of this study is that the interviewees were not familiar with the new, green pavement known as IBS StormPav. Information on its actual performance and durability are not yet known since this pavement has yet to be implemented. Therefore, there is no data that can support the theories about this pavement. Besides that, the surface temperature data for the IBS pavement could be more accurate if thermocouples were utilized. An accurate temperature can be obtained from inside the pavement by installing thermocouples on the inner top and bottom of the pavement. However, the surface temperature obtained from the outside of this pavement using ThermaCam is also sufficient and representative of the nature of the pavement. The recorded temperatures prove that this pavement absorbs less heat than asphalt and has similar characteristics to normal concrete pavement.
For future research, investigation of the thermal behavior and heat impact of the vertical surfaces of buildings should be conducted regarding their mitigation or intensification factors on UHI. This study will be based on the materials of buildings that are typically used in Malaysia: concrete, brick, white concrete tiles, and granite. This study could be implemented in the hottest area of Kuching. The data collection will include the hourly surface temperatures for 12 hours using ThermaCam and the air temperature using an anemometer. This future study can improve the knowledge and understanding of other factors that contribute to the UHI phenomenon.
The authors wish to thank the Faculty of Engineering (Universiti Malaysia Sarawak) for the opportunity to undertake this project, Jabatan Kerja Raya Sarawak and Jabatan Kerja Raya Batu Lintang for the support to complete this research.
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