228 Ow et al: Benefits of Tree Shade and Turf in an Urban Environment Arboriculture & Urban Forestry 2020. 46(3):228–244 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & The Benefits of Tree Shade and Turf on Globe and Surface Temperatures in an Urban Tropical Environment By Lai Fern Ow, Subhadip Ghosh, and Mohamed Lokman Mohd Yusof Abstract. The process of urbanisation increases temperature and alters the thermal comfort in cities. Urban heat islands (UHIs) result in the rise of ambient temperatures. For example, in the densely populated island state of Singapore, the UHI intensity was some 4.5 °C. Such elevation in heat can negatively impact outdoor thermal comfort and may give rise to serious health problems. The present study investigated the bene- fits of trees and turf as mitigation strategies for urban areas. Short- and long-term observations were made for surface and globe temperatures over smaller plots of vegetation and hard surfaces involving tree shade and full sun. Similar observations were investigated over a larger extent of vegetation across concrete, asphalt, and turf within an urban park setting. The presence of turf and shade from trees greatly affected surface temperatures, and the effect was most pronounced when both were present. The presence of turf reduced surface temperatures by up to 10 °C, while tree shade led to a 12 °C reduction. Globe temperatures showed that the presence of turf and shading reduced temperatures between 5 and 10 °C. These results suggest that turf and trees can effectively cool surfaces and improve outdoor thermal comfort. The results of this study can be applied to urban planning of greenery and can be used as a reference for other tropical cities with similar climates that are also working to develop mitigation measures to improve the liveability of their cities. Keywords. Globe Temperature; Surface Temperature; Tree Shade; Turf; Urban Environments. INTRODUCTION The effects of the urban heat island (UHI) had been studied extensively in the last decade. Built surfaces, such as concrete, asphalt, and bricks, found in urban areas, absorb heat during the day, and the absorbed heat is re-radiated back into the environment (Arn- field 2003; Kuttler 2008). The temperature differen- tial is larger at night than during the day, and this becomes more pronounced when winds are weak. For example, Jusuf et al. (2007) showed that in the day and within an urban city, the effect of UHI on sur- face temperature for various land use types was in the order of industrial, commercial, airport, residential, and park, respectively, while at night, the order changes to commercial, residential, park, industrial, and airport. Similarly, Rinner and Hussain (2011) also confirmed that there was higher average surface temperature for commercial and industrial land use and lower average surface temperature for parks and ©2020 International Society of Arboriculture water bodies. The relationships between land use and the UHI effect were further reinforced in the work conducted by Zhang et al. (2013) in Shanghai, China. The effect of UHI enhances with land surface modification. For example, the loss of vegetation reduces the reflection of solar radiation. Additionally, this change negatively impacts on evapotranspira- tional cooling. The effect of UHI in various urban centres can result in temperature increments of between 4.5 and 7 °C (Imhoff et al. 2010). The urban heat island is more pronounced in humid tropical environments where the increase in temperature exacerbates the requirement for air conditioning indoors, but this, in turn, causes thermal discomfort to people outdoors. The effect of the UHI is likely to escalate with climate change, as mean ambient tem- peratures are set to rise. For instance, if nothing is done to combat global warming, temperature projec- tions for Asia are set to rise by 4.8 °C by the year
May 2020
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