scholarly journals Potential for Application of Retroreflective Materials instead of Highly Reflective Materials for Urban Heat Island Mitigation

2016 ◽  
Vol 2016 ◽  
pp. 1-10 ◽  
Author(s):  
Jihui Yuan ◽  
Kazuo Emura ◽  
Craig Farnham
Keyword(s):  
Solar Radiation ◽  
Urban Heat Island ◽  
Air Conditioning ◽  
Green Roofs ◽  
Heat Sinks ◽  
Heat Island ◽  
Limited Effect ◽  
Building Envelopes ◽  
Urban Heat ◽  
Cool Roofs

Research on urban heat island (UHI) mitigation has been carried out globally. Several strategies have been proposed or developed to mitigate UHI, including highly reflective (HR) envelopes of buildings, green roofs, urban vegetation, shading, heat sinks, and air-conditioning efficiency. Among these techniques, HR envelopes have been extensively studied as an effective method to mitigate the UHI effect by reducing energy consumption. However, because most of HR materials are diffusive, HR envelopes applied to vertical surfaces can reflect both onto roads and nearby buildings. Additionally, HR roofs cannot reflect all incoming solar radiation to the sky if there are high buildings around it. Thus, HR materials applied as building envelopes have a limited effect against the solar contribution to the UHI. In order to solve this problem, retroreflective (RR) materials, which reflect the solar radiation back towards the source, have been studied and developed to be applied as building envelopes instead of HR materials. This paper summarizes several previous researches on HR envelopes and cool roofs and summarizes several current researches on RR materials. The potential for application of RR envelopes in cities is proposed with consideration of economic and environmental factors.

Cool Roofs vs Solar Systems

2016 ◽  
Vol 824 ◽  
pp. 779-785
Author(s):  
Dominika Kassai-Szoó ◽  
András Zöld
Keyword(s):  
Solar Radiation ◽  
Urban Heat Island ◽  
Urban Climate ◽  
Tall Buildings ◽  
Point Of View ◽  
Heat Island ◽  
Solar Systems ◽  
Negative Effect ◽  
Urban Heat ◽  
Cool Roofs

Well known problem of urban heat island is partly due to the albedo of traditional roofs. Mostexperts of urban climate are convinced that the intensity of urban heat island will be less if theroofs reflect as big part of the solar radiation as possible. Researchers have found or developedappropriate materials of low absorptance in the wavelength spectrum of solar radiation together with high emissivity in the long infrared interval. As a result, roof covering may have such extraparameters as metal roof painted with colored cool coating has 0.8 reflectance and 0.8 emittanceindex or single ply-membrane white (PVC) has 0.7 reflectance and 0.8 emittance index.No doubt taking into account the settlement as a whole cool roofs may decrease the intensity ofurban heat island however some local negative effect should not be forgotten. Approaching the citycenter it is typical that low rise and tall buildings are nearby. In some cases the same buildinghas high and low rise wings, from the point of view of geometry similar is the situation between thefacade and a canopy or a balcony. In this case the radiation reflect by the horizontal surfaceconsiderably increases the load on the facade, in this paper the relevant cases are analysed and thecalculated extra load and its consequences are evaluated.

scholarly journals Effectiveness of Different Urban Heat Island Mitigation Methods and Their Regional Impacts

2017 ◽  
Vol 18 (11) ◽  
pp. 2991-3012 ◽  
Author(s):  
Ning Zhang ◽  
Yan Chen ◽  
Ling Luo ◽  
Yongwei Wang
Keyword(s):  
Boundary Layer ◽  
Urban Heat Island ◽  
Air Temperature ◽  
Surface Air Temperature ◽  
Green Roofs ◽  
Heat Island ◽  
Near Surface ◽  
Regional Impacts ◽  
Urban Heat ◽  
Cool Roofs

Abstract Cool roofs and green roofs are two popular methods to mitigate the urban heat island and improve urban climates. The effectiveness of different urban heat island mitigation strategies in the summer of 2013 in the Yangtze River delta, China, is investigated using the Weather Research and Forecasting (WRF) Model coupled with a physically based single-layer urban canopy model. The modifications to the roof surface changed the urban surface radiation balance and then modified the local surface energy budget. Both cool roofs and green roofs led to a lower surface skin temperature and near-surface air temperature. Increasing the roof albedo to 0.5 caused a similar effectiveness as covering 25% of urban roofs with vegetation; increasing the roof albedo to 0.7 caused a similar near-surface air temperature decrease as 50% green roof coverage. The near-surface relative humidity increased in both cool roof and green roof experiments because of the combination of the impacts of increases in specific humidity and decreases in air temperature. The regional impacts of cool roofs and green roofs were evaluated using a regional effect index. A regional impact was found for near-surface air temperature and specific/relative humidity when the percentage of roofs covered with high-albedo materials or green roofs reached a higher fraction (greater than 50%). The changes in the vertical profiles of temperature cause a more stable atmospheric boundary layer over the urban area; at the same time, the crossover phenomena occurred above the boundary layer due to the decrease in vertical wind speed.

URBAN HEAT ISLAND MITIGATION USING GREEN ROOF APPROACH

2018 ◽  
Vol 80 (3) ◽  
Author(s):  
Johan Sohaili ◽  
Leong Kar Yan ◽  
Shantha Kumari Muniyandi ◽  
Siti Suhaila Mohamad
Keyword(s):  
Air Pollution ◽  
Solar Radiation ◽  
Urban Heat Island ◽  
Air Pollutants ◽  
Green Roof ◽  
Green Roofs ◽  
Urban Environments ◽  
Heat Island ◽  
Urban Heat ◽  
Reduced Temperature

In urban environments, vegetation has largely been replaced by impervious and often dark surfaces. These conditions contribute to an Urban Heat Island (UHI) effect. This phenomenon is demonstrated in many cities and produced effects such as higher atmospheric temperatures, intensive precipitation, excessive solar radiation and increasing air pollution. Therefore, reducing the surface temperature of roofs in a building may play an important role in improving the conventional roof surfaces with green roofs that offer much lower temperatures throughout a day to reach their thermal performance and reduce the absorption of solar radiation. Thus, this study is focused on determining the effectiveness of the existing green roof in reducing the ambient temperature and humidity of the air above it by comparison with conventional open roof top without vegetation. This study also aims to evaluate the potential of green roof to reduce the air pollutants in improving air quality in urban cities. As a result, by adopting green roof system, it has reduced temperature during the hottest hour in a day at 1230 hour (hr) by 4.3°C when compared to open roof. Green roof has also recorded higher percentage of humidity compared to open roof. Most importantly, it was proven through this study that green roof has the potential of absorbing pollutants in the air by reducing the concentrations of Sulphur dioxide (SO2), Ammonia (NH3), Nitrogen dioxide (NO2), Ozone (O3) and Carbon monoxide (CO) compared to open roof. Thus, green roofs can be considered to be one of the effective methods to mitigate UHI effects in urban cities.

scholarly journals The Effects of Green Roofs on Outdoor Thermal Comfort, Urban Heat Island Mitigation and Energy Savings

Atmosphere ◽  
2020 ◽  
Vol 11 (2) ◽  
pp. 123 ◽  
Author(s):  
Guglielmina Mutani ◽  
Valeria Todeschi
Keyword(s):  
Surface Temperature ◽  
Thermal Comfort ◽  
Urban Heat Island ◽  
Land Surface Temperature ◽  
Land Surface ◽  
Green Roofs ◽  
Heat Island ◽  
Urban Context ◽  
Urban Heat ◽  
The City

There is growing attention to the use of greenery in urban areas, in various forms and functions, as an instrument to reduce the impact of human activities on the urban environment. The aim of this study has been to investigate the use of green roofs as a strategy to reduce the urban heat island effect and to improve the thermal comfort of indoor and outdoor environments. The effects of the built-up environment, the presence of vegetation and green roofs, and the urban morphology of the city of Turin (Italy) have been assessed considering the land surface temperature distribution. This analysis has considered all the information recorded by the local weather stations and satellite images, and compares it with the geometrical and typological characteristics of the city in order to find correlations that confirm that greenery and vegetation improve the livability of an urban context. The results demonstrate that the land-surface temperature, and therefore the air temperature, tend to decrease as the green areas increase. This trend depends on the type of urban context. Based on the results of a green-roofs investigation of Turin, the existing and potential green roofs are respectively almost 300 (257,380 m2) and 15,450 (6,787,929 m2). Based on potential assessment, a strategy of priority was established according to the characteristics of building, to the presence of empty spaces, and to the identification of critical areas, in which the thermal comfort conditions are poor with low vegetation. This approach can be useful to help stakeholders, urban planners, and policy makers to effectively mitigate the urban heat island (UHI), improve the livability of the city, reduce greenhouse gas (GHG) emissions and gain thermal comfort conditions, and to identify policies and incentives to promote green roofs.

Green and cool roofs’ urban heat island mitigation potential in tropical climate

Solar Energy ◽  
2018 ◽  
Vol 173 ◽  
pp. 597-609 ◽  
Author(s):  
Junjing Yang ◽  
Devi llamathy Mohan Kumar ◽  
Andri Pyrgou ◽  
Adrian Chong ◽  
Mat Santamouris ◽  
...  
Keyword(s):  
Urban Heat Island ◽  
Tropical Climate ◽  
Heat Island ◽  
Mitigation Potential ◽  
Urban Heat ◽  
Cool Roofs

scholarly journals Mitigating Urban Heat Island Through Green Roofs

2015 ◽  
Vol 10 (Special-Issue1) ◽  
pp. 918-927 ◽  
Author(s):  
Roozbeh Arabi ◽  
Mohd Shahidan ◽  
M. S Kamal ◽  
Mohamad Jaafar ◽  
Mehdi Rakhshandehroo
Keyword(s):  
Urban Heat Island ◽  
Green Roofs ◽  
Heat Island ◽  
Urban Heat

scholarly journals Analysis of Urban Heat Island and Heat Waves Using Sentinel-3 Images: a Study of Andalusian Cities in Spain

2021 ◽  
Author(s):  
David Hidalgo García
Keyword(s):  
Solar Radiation ◽  
Urban Heat Island ◽  
Heat Wave ◽  
Land Surface ◽  
Heat Waves ◽  
Economic Cost ◽  
Heat Island ◽  
Multivariate Relationships ◽  
Urban Heat ◽  
Wave Conditions

Abstract At present, understanding the synergies between the Surface Urban Heat Island (SUHI) phenomenon and extreme climatic events entailing high mortality, i.e., heat waves, is a great challenge that must be faced to improve the quality of life in urban zones. The implementation of new mitigation and resilience measures in cities would serve to lessen the effects of heat waves and the economic cost they entail. In this research, the Land Surface Temperature (LST) and the SUHI were determined through Sentinel-3A and 3B images of the eight capitals of Andalusia (southern Spain) during the months of July and August of years 2019 and 2020. The objective was to determine possible synergies or interaction between the LST and SUHI, as well as between SUHI and heat waves, in a region classified as highly vulnerable to the effects of climate change. For each Andalusian city, the atmospheric variables of ambient temperature, solar radiation, wind speed and direction were obtained from stations of the Spanish State Meteorological Agency (AEMET); the data were quantified and classified both in periods of normal environmental conditions and during heat waves. By means of Data Panel statistical analysis, the multivariate relationships were derived, determining which ones statistically influence the SUHI during heat wave periods. The results indicate that the LST and the mean SUHI obtained are statistically interacted and intensify under heat wave conditions. The greatest increases in daytime temperatures were seen for Sentinel-3A in cities by the coast (LST = 3.90 °C, SUHI = 1.44 °C) and for Sentinel-3B in cities located inland (LST = 2.85 °C, SUHI = 0.52 °C). The existence of statistically significant positive relationships above 99% (p < 0.000) between the SUHI and solar radiation, and between the SUHI and the direction of the wind, intensified in periods of heat wave, could be verified. An increase in the urban area affected by the SUHI under heat wave conditions is reported. Graphical Abstract

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