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The effect of urban density and vegetation cover on the heat island of a subtropical city

The urban heat island (UHI) has a negative impact on the health of urban residents by increasing average temperatures. The intensity of the UHI effect is influenced by urban geometry and the amount of vegetation cover. This study investigated the impact of urban growth and loss of vegetation cover on the UHI in a subtropical city (Brisbane, Australia) during average and extreme conditions using the Conformal Cubic Atmospheric Model, run at a 1-km spatial resolution for 10 years. The average nighttime temperature increase was 0.7°C for the “Medium Density” urban growth scenario and 1.8°C for the “No Vegetation” scenario. During two widespread extreme heat events, the mean maximum increase in urban temperatures above the Control was between 2.2° and 3.8°C in the No Vegetation scenario and between 0.3° and 1.6°C in the Medium Density urban growth scenario. The results are similar to previous findings for temperate cities, with the intensity of the UHI effect higher at night and during winter than during the day and summer. Vegetation cover had the strongest impact on temperatures, more so than building height and height/width ratio. Maintaining and restoring vegetation, therefore, is a key consideration in mitigating the urban heat island. The large temperature increases found in this study, particularly during extreme heat events, shows the importance of reducing the UHI for protecting the health of urban residents, and this should be a priority in urban landscape planning and design.

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