A Study of Urban Heat Island using “Local Climate Zones” – The Case of Singapore

Abstract

Aims: The study of urban heat islands and traditionally relies on simplistic descriptors such as “urban” and “rural”. While these descriptors may be evocative of the landscape, they are insufficient in providing information like its site properties which have direct impacts on the surface-layer climate. The newly developed “Local Climate Zones” (LCZ) characterization scheme from Oke and Stewart [1] was applied to three case study areas to provide a more objective assessment of the urban heat island (UHI) phenomenon in Singapore. Study Design: The three step procedure of site metadata collection, definition of the thermal source area, and selection of the appropriate climate zone was followed for the three case study areas representing green space, a typical high rise residential housing area, and the CBD to identify and explain UHI characteristics. Place and Duration of Study: Singapore; January-March, 2014. Methodology: Characterization of the three study sites included scoring of a sky view factor, canyon aspect ratio, terrain roughness, building surface fraction, impervious surface fraction, surface energy admittance, surface albedo, and anthropogenic heat flux based on observation, photography, and Google Earth imagery, to determine the LCZ class. Temperature, wind speed, and relative humidity were recorded on an hourly basis at each site using Kestrel 4000 weather trackers and data logger at a 2 m elevation for five consecutive days in January, 2014. Results: The three study sites were characterized as LCZ 1 (compact high rise (CBD)), LCZ 4 (open high rise (high rise residential housing area)), and LCZ 9 (sparsely built (green space)). The temperature for LCZ 9 was lower than the other two sites, with the greatest UHI intensity (difference between mean air temperature being 2.01ºC between LCZ 4 and LCZ 9. Interestingly, although the CBD area was warmer than the open high rise area between midnight and 6 a.m., a typical UHI phenomenon, the mean air temperature for the entire 5 day period was greater at the open rise site. Conclusion: The lower temperature at the green space site emphasizes the importance of such spaces in the urban landscape as a means to make cities more liveable and resilient to climate change impacts. The higher mean temperature at the open high rise site as compared to the CBD site was related to anthropogenic activities (particularly traffic patterns), landscaping/green space, and the influence of a large green-certified building within the circle of influence at the CBD site. Overall, the use of LCZ in quantifying the UHI magnitude of Singapore was relatively straightforward to apply and this approach should be widely applied to more objectively investigate the UHI phenomenon, particularly in tropical cities.