Assessment of the Water Pond Cooling Effect on Urban Microclimate: A Parametric Study with Numerical Modeling

Effective utilization of urban surface modification and landscaping through appropriate planning and design is becoming increasingly important. In contrast to the large number of studies on urban microclimates, few studies have directly focused on the outdoor thermal environment, in particular those investigating the role of water bodies. To optimize the usage of water bodies and to identify the distinguishing factors that may affect the benefits of cooling, a coupled computational fluid dynamics calculation and surface temperature calculation were used to estimate the cooling influence of water bodies on urban microclimates. The study presented in this paper simulated nine unique cases of a simplified urban neighborhood to evaluate the unique effect of different water pond configurations. In summary, within the urban canyon, the study results highlight the importance of a water body’s configuration and positioning. Relative to prevailing winds, larger water pond surfaces tended to produce a better thermal environment, while equally distributed water ponds seemed to influence a wider area.

Cooling effect; Numerical modeling; Thermal environment; Urban canyon; Water body

        Considerable variations in land usage, land cover, and urban surface texture in a city contribute to various urban problems, such as an urban heat island (UHI). UHI, where the urban area is warmer than the rural area, affects a building’s energy consumption as well as the occupant’s thermal comfort, health, and well-being (Brontowiyono et al., 2011; Wibowo and Salleh, 2018; Ibrahim et al., 2018). This generates interest among planners and designers in UHI mitigating strategies. Although still limited, research has beenconducted on a water body’s ability to ameliorate a warm urban microclimate. Generally, these studies have shown that the air temperature is 1–5°C lower near water bodies (e.g., lakes, rivers, wetlands, and ponds) in comparison to adjacent built-up areas, particularly during the day (Jusuf et al., 2009; Völker et al., 2013; Lu et al., 2017; Jin et al., 2017; Syafii et al., 2017a; Cai et al., 2018; Jacobs et al., 2020). However, there is still a lack of design consideration in arranging effective water bodies to improve urban thermal environments. Therefore, further investigation is needed to verify the mitigating capacity of water bodies and to advance the current understanding of the influential factors that may be useful for planners and designers.

This paper presented the results from a parametric study with a hypothetically urban neighborhood in which the water surface area, spatial configuration, and water temperature were varied. Most of the factors affecting cooling of air temperature (pond sizes, arrangements, and thermal capacity) were considered. Coupled numerical modeling, surface temperature calculation, and CFD calculation were used to obtain a better understanding of the effects of these influential factors and to determine the most effective design consideration for a water body’s application inside the urban canyon, where buildings and other urban elements might influence a pond’s microclimate benefits. Parametric studies using numerical simulation have the advantage of allowing a broad sample of urban surface modifications to be analyzed and compared, thanks to the rapid development of computational technology.

The results show that the air temperature is lower near water bodies than near a hard surface (concrete). The water body's ability to reduce the air temperature can be seen as a positive indicator for achieving enhanced thermal environments. Furthermore, the cooling effect of water bodies in urban canyons is influenced by, and depends on, the size and distribution of the water bodies with respect to wind speed and direction. Generally, with the same water surface area, the cases with EQD configurations were able to influence a much larger area of the canyon while the cases with centered configurations tended to generate a greater amount of cool air. Additionally, by keeping the water temperature low, the cooling intensity from the ponds increased significantly. The greatest effect from the chilled water pond occurred in the larger bodies of water.

        However, the current study is limited to a simplified urban residential microclimate. Due to the complexity of the urban structure, surface materials, and other factors, the study’s conclusion may not be appropriate for higher-density urban city spaces. Thus, potential future research on the cooling impact of water bodies could include factors, such as the influence of other types of water bodies (e.g., flowing water, water spray, water wall, etc.) in combination with other surface modifications (e.g., trees, shading devices, etc.), a more detailed water bodies form factor, or even exposure to a different predominant microclimate. Furthermore, the current study demonstrates the possibility of enhancing the cooling benefits of water bodies by introducing chilled water, which needs further investigation.

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