Abstract
Adaptation to prepare for adverse climate change impacts in the context of urban heat islands and outdoor thermal comfort (OTC) is receiving growing concern. However, knowledge of quantitative microclimatic conditions within the urban boundary layer in the future is still lacking, such that the introduction of adequate adaptation measures to increase OTC is challenging. To investigate the cooling performance of a water spraying system in a sub-tropical compact and high-rise built environment in summer under the influence of future (2050) climatic conditions, results from two validated models (Weather Research and Forecast (WRF) and ENVI-met models) have been used and analyzed. Our results indicate that the spraying system provides cooling of 2–3 °C for ambient air temperature at the pedestrian-level of the urban canyons considered here, which benefits pedestrians. However, improvement of the OTC in terms of the physiological equivalent temperature (PET—a better indicator of human thermal sensation) was noticeable (e.g., <42 °C or from very hot to hot) when the urban canyon was orientated parallel to the prevailing wind direction only. This implies that in order to improve city resilience in terms of heat stress, more holistic adaptation measures in urban planning are needed. This includes the introduction of more breezeways and building disposition to facilitate the urban ventilation, as well as urban tree arrangement and sunshades to reduce direct solar radiation to plan for the impact of future climate change.
Highlights
The urban heat island (UHI), which features higher air and surface temperatures in urban areas relative to rural areas, affects the human health [1] and deteriorates the quality of urban living in sub-tropical and tropical regions
A noticeable is consistent with a study in Japan, which reported that the cooling effect of the water air temperature drop of more than 2 °C was found up to 17 m above ground level (AGL)
Since the ambient air temperature in the future (2050) could be increased by more than 4 ◦ C relative to the current situation, climate change adaptation measures to reduce heat stress in urban areas are urgently needed. This is especially true as physiological equivalent temperature (PET) were calculated to be 5 ◦ C higher in the urban street canyons than those in the ambient open areas in our study due to the low wind speeds in the urban canyons
Summary
The urban heat island (UHI), which features higher air and surface temperatures in urban areas relative to rural areas, affects the human health [1] and deteriorates the quality of urban living in sub-tropical and tropical regions. Multiple reflections of solar radiation within the urban street canyons increase the heat stored in the built environment. Climate change presents negative effects (e.g., via increasing ambient air temperature) to the built environment and OTC [2,3], and, receives growing concern [4,5,6]. The maximum increases in global average surface air temperature of 2 ◦ C and 4 ◦ C in 2050 and 2010, respectively, have projected by the Intergovernmental Panel on Climate Change (IPCC; [7]). Quantification of the climate change impact on the urban built environment remains challenging.
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