A platform for research: civil engineering, architecture and urbanism
A platform for research: civil engineering, architecture and urbanism
Cool roof strategies for urban thermal resilience to extreme heatwaves in tropical cities
https://orcid.org/0000-0002-7869-1150
https://orcid.org/0000-0002-1049-082X
Graphical abstract Display Omitted
Highlights Cool roofs reduce peak ambient and surface temperatures by 2.3 °C and, 6.1 °C respectively. Cool roofs lower average night ambient and surface temperatures by 1.1 °C and, 4.1 °C respectively. Cool roofs can lower the planetary boundary layer height by up to 1978.5 m. Sea breeze onset may delay during peak temperatures due to the regional high effect. Outdoor comfort improves, with the index decreasing by up to 1.8 °C during peak hours.
Abstract Extreme heatwaves in tropical cities represent a significant short-term weather challenge, directly impacting urban heat, exacerbating human discomfort, and increasing energy demands. To alleviate this, meteorological adjustments utilizing reflective roofing technologies, such as cool roofs, can effectively mitigate heatwave-induced excess heat and enhance thermal comfort. This study assessed the effectiveness of cool roofs in cooling urban areas following heatwaves in Kolkata, India, using comprehensive city-scale simulations. The study presumed that the existing roofing materials, with a reflectivity of 0.15 and emissivity of 0.85, indicated the unmitigated condition. These materials were replaced with third-generation cool roof materials featuring a reflectivity of 0.80 and emissivity of 0.85, leading to a substantial improvement in urban meteorology and thermal comfort compared to the unmitigated state. Notably, during heatwave episodes, the most significant computed reductions in energy flux were 181.3 Wm−2, 16.6 Wm−2, 56.3 Wm−2, and 251.9 Wm−2 for sensible heat, latent heat, ground storage, and net inflow radiation, respectively. Consequently, this led to decreases of 2.3 °C, 6.1 °C, 21.8 °C, and 1.9 °C in urban thermal parameters during peak hours (14:00 LT) for ambient temperature, surface temperature, roof surface temperature, and urban canopy temperature, respectively. The maximum drops in the planetary boundary layer (PBL) were 130.6 m, 1978.5 m, and 1010.3 m for 6:00 LT, 14:00 LT, and 18:00 LT, with an average of 870.3 m. Cool roofs demonstrated their potential to minimize thermal stress during heatwave periods, showcasing a maximum drop in the heat stress index (HSI) of up to 1.5 °C in the morning. Furthermore, outdoor thermal comfort could be significantly enhanced by lowering the universal thermal comfort index (UTCI) at the near surface, resulting in reductions of up to 1.8 °C during peak hours. On average, there was a reduction in UTCI between day and night of approximately 1.2 °C and 0.7 °C in densely populated urban areas. Additionally, the study evaluated 32 case studies that focused on cool roof strategies, revealing remarkably consistent findings that suggest a plausible justification. These findings provide a valuable framework for urban planners and policymakers considering the integration of cool roofs-based heat reduction technology at the city scale.
Cool roof strategies for urban thermal resilience to extreme heatwaves in tropical cities
https://orcid.org/0000-0002-7869-1150
https://orcid.org/0000-0002-1049-082X
Graphical abstract Display Omitted
Highlights Cool roofs reduce peak ambient and surface temperatures by 2.3 °C and, 6.1 °C respectively. Cool roofs lower average night ambient and surface temperatures by 1.1 °C and, 4.1 °C respectively. Cool roofs can lower the planetary boundary layer height by up to 1978.5 m. Sea breeze onset may delay during peak temperatures due to the regional high effect. Outdoor comfort improves, with the index decreasing by up to 1.8 °C during peak hours.
Abstract Extreme heatwaves in tropical cities represent a significant short-term weather challenge, directly impacting urban heat, exacerbating human discomfort, and increasing energy demands. To alleviate this, meteorological adjustments utilizing reflective roofing technologies, such as cool roofs, can effectively mitigate heatwave-induced excess heat and enhance thermal comfort. This study assessed the effectiveness of cool roofs in cooling urban areas following heatwaves in Kolkata, India, using comprehensive city-scale simulations. The study presumed that the existing roofing materials, with a reflectivity of 0.15 and emissivity of 0.85, indicated the unmitigated condition. These materials were replaced with third-generation cool roof materials featuring a reflectivity of 0.80 and emissivity of 0.85, leading to a substantial improvement in urban meteorology and thermal comfort compared to the unmitigated state. Notably, during heatwave episodes, the most significant computed reductions in energy flux were 181.3 Wm−2, 16.6 Wm−2, 56.3 Wm−2, and 251.9 Wm−2 for sensible heat, latent heat, ground storage, and net inflow radiation, respectively. Consequently, this led to decreases of 2.3 °C, 6.1 °C, 21.8 °C, and 1.9 °C in urban thermal parameters during peak hours (14:00 LT) for ambient temperature, surface temperature, roof surface temperature, and urban canopy temperature, respectively. The maximum drops in the planetary boundary layer (PBL) were 130.6 m, 1978.5 m, and 1010.3 m for 6:00 LT, 14:00 LT, and 18:00 LT, with an average of 870.3 m. Cool roofs demonstrated their potential to minimize thermal stress during heatwave periods, showcasing a maximum drop in the heat stress index (HSI) of up to 1.5 °C in the morning. Furthermore, outdoor thermal comfort could be significantly enhanced by lowering the universal thermal comfort index (UTCI) at the near surface, resulting in reductions of up to 1.8 °C during peak hours. On average, there was a reduction in UTCI between day and night of approximately 1.2 °C and 0.7 °C in densely populated urban areas. Additionally, the study evaluated 32 case studies that focused on cool roof strategies, revealing remarkably consistent findings that suggest a plausible justification. These findings provide a valuable framework for urban planners and policymakers considering the integration of cool roofs-based heat reduction technology at the city scale.
Cool roof strategies for urban thermal resilience to extreme heatwaves in tropical cities
https://orcid.org/0000-0002-7869-1150
https://orcid.org/0000-0002-1049-082X
Graphical abstract Display Omitted
Highlights Cool roofs reduce peak ambient and surface temperatures by 2.3 °C and, 6.1 °C respectively. Cool roofs lower average night ambient and surface temperatures by 1.1 °C and, 4.1 °C respectively. Cool roofs can lower the planetary boundary layer height by up to 1978.5 m. Sea breeze onset may delay during peak temperatures due to the regional high effect. Outdoor comfort improves, with the index decreasing by up to 1.8 °C during peak hours.
Abstract Extreme heatwaves in tropical cities represent a significant short-term weather challenge, directly impacting urban heat, exacerbating human discomfort, and increasing energy demands. To alleviate this, meteorological adjustments utilizing reflective roofing technologies, such as cool roofs, can effectively mitigate heatwave-induced excess heat and enhance thermal comfort. This study assessed the effectiveness of cool roofs in cooling urban areas following heatwaves in Kolkata, India, using comprehensive city-scale simulations. The study presumed that the existing roofing materials, with a reflectivity of 0.15 and emissivity of 0.85, indicated the unmitigated condition. These materials were replaced with third-generation cool roof materials featuring a reflectivity of 0.80 and emissivity of 0.85, leading to a substantial improvement in urban meteorology and thermal comfort compared to the unmitigated state. Notably, during heatwave episodes, the most significant computed reductions in energy flux were 181.3 Wm−2, 16.6 Wm−2, 56.3 Wm−2, and 251.9 Wm−2 for sensible heat, latent heat, ground storage, and net inflow radiation, respectively. Consequently, this led to decreases of 2.3 °C, 6.1 °C, 21.8 °C, and 1.9 °C in urban thermal parameters during peak hours (14:00 LT) for ambient temperature, surface temperature, roof surface temperature, and urban canopy temperature, respectively. The maximum drops in the planetary boundary layer (PBL) were 130.6 m, 1978.5 m, and 1010.3 m for 6:00 LT, 14:00 LT, and 18:00 LT, with an average of 870.3 m. Cool roofs demonstrated their potential to minimize thermal stress during heatwave periods, showcasing a maximum drop in the heat stress index (HSI) of up to 1.5 °C in the morning. Furthermore, outdoor thermal comfort could be significantly enhanced by lowering the universal thermal comfort index (UTCI) at the near surface, resulting in reductions of up to 1.8 °C during peak hours. On average, there was a reduction in UTCI between day and night of approximately 1.2 °C and 0.7 °C in densely populated urban areas. Additionally, the study evaluated 32 case studies that focused on cool roof strategies, revealing remarkably consistent findings that suggest a plausible justification. These findings provide a valuable framework for urban planners and policymakers considering the integration of cool roofs-based heat reduction technology at the city scale.
Cool roof strategies for urban thermal resilience to extreme heatwaves in tropical cities
Khorat, Samiran (author) / Das, Debashish (author) / Khatun, Rupali (author) / Aziz, Sk Mohammad (author) / Anand, Prashant (author) / Khan, Ansar (author) / Santamouris, Mattheos (author) / Niyogi, Dev (author)
Energy and Buildings ; 302
2023-11-13
Article (Journal)
Electronic Resource
English
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