Abstract
This paper presents a literature review on urban design indicators addressing the impact of urban geometry and vegetation on the outdoor thermal environment at the pedestrian level, as urban geometry and vegetation have been regarded as the most influential urban design factors that affect outdoor microclimate. The thermal balance concept is first introduced to elaborate how each component of energy fluxes is affected by the urban built environment, which helps to explore the underlying thermophysical mechanisms of how urban design modifies the outdoor thermal environment. The literature on numerous urban design descriptors addressing urban geometric characteristics is categorized into five groups in this paper according to the design features that the parameters entail, including land use intensity, building form, canyon geometry, space enclosure and descriptive characteristics. The literature on urban vegetation descriptors is reviewed together, followed by the combined effect of urban geometry and vegetation. This paper identifies a series of important urban design parameters and shows that the impact of design parameters on thermal environment varies with time, season, local climate and urban contexts. Contradictory impacts often occur between daytime and nighttime, or different seasons, which requests trade-offs to be achieved when proposing design strategies.
Highlights
Accelerated world population growth and urbanization rate have caused considerable stress to our environment: for instance, environmental degradation and climate change
Computational fluid dynamic (CFD) simulations were conducted in Singapore and the results showed that applying an ideal H/W ratio for urban canyons would increase the wind speed by up to 35% and cool the air by up to 0.7 ◦ C [59]
Urban design and architectural design professionals have taken climate into consideration since early constructions in the human history, the design decisions were mostly made based on personal experiences and a common understanding of local climate effects accumulated from generation to generation
Summary
Accelerated world population growth and urbanization rate have caused considerable stress to our environment: for instance, environmental degradation and climate change. Evidence of the negative influences of UHI on energy consumption, air pollution, and public health began to accumulate decades ago. UHI could amplify the cooling energy load substantially in the summer, especially for hot areas [7,8]. According to Salvati, Coch Roura, and Cecere [9], the simulation showed that the cooling load of residential buildings can be increased by the local UHI intensity (2.8 ◦ C in winter and 1.7 ◦ C in summer) by around 18–28%. UHI effect was found to have a significant influence on extreme weather incidents, such as heat waves [11], which is highly related to public health and mortality rates [12,13,14]
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