The effectiveness of cool and green roofs as urban heat island mitigation strategies

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.

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Green Infrastructure as an Urban Heat Island Mitigation Strategy—A Review

Water ◽

10.3390/w12123577 ◽

2020 ◽

Vol 12 (12) ◽

pp. 3577

Author(s):

Fatma Balany ◽

Anne WM Ng ◽

Nitin Muttil ◽

Shobha Muthukumaran ◽

Man Sing Wong

Keyword(s):

Thermal Comfort ◽

Urban Heat Island ◽

Green Infrastructure ◽

Mitigation Strategies ◽

Heat Island ◽

Recent Past ◽

Simulation Tools ◽

Human Thermal Comfort ◽

Different Types ◽

Urban Heat

Research on urban heat mitigation has been growing in recent years with many of the studies focusing on green infrastructure (GI) as a strategy to mitigate the adverse effects of an urban heat island (UHI). This paper aims at presenting a review of the range of findings from GI research for urban heat mitigation through a review of scientific articles published during the years 2009–2020. This research includes a review of the different types of GI and its contribution for urban heat mitigation and human thermal comfort. In addition to analysing different mitigation strategies, numerical simulation tools that are commonly used are also reviewed. It is seen that ENVI-met is one of the modelling tools that is considered as a reliable to simulate different mitigation strategies and hence has been widely used in the recent past. Considering its popularity in urban microclimate studies, this article also provides a review of ENVI-met simulation results that were reported in the reviewed papers. It was observed that the majority of the research was conducted on a limited spatial scale and focused on temperature and human thermal comfort.

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Mitigating the Urban Heat Island Effect in Megacity Tehran

Advances in Meteorology ◽

10.1155/2014/547974 ◽

2014 ◽

Vol 2014 ◽

pp. 1-19 ◽

Cited By ~ 35

Author(s):

Sahar Sodoudi ◽

Parisa Shahmohamadi ◽

Ken Vollack ◽

Ulrich Cubasch ◽

A. I. Che-Ani

Keyword(s):

Urban Heat Island ◽

Rural Areas ◽

Heat Waves ◽

Mitigation Strategies ◽

Cooling Effect ◽

Heat Island ◽

Microscale Model ◽

Negative Effect ◽

Urban Heat ◽

Surrounding Areas

Cities demonstrate higher nocturnal temperatures than surrounding rural areas, which is called “urban heat island” (UHI) effect. Climate change projections also indicate increase in the frequency and intensity of heat waves, which will intensify the UHI effect. As megacity Tehran is affected by severe heatwaves in summer, this study investigates its UHI characteristics and suggests some feasible mitigation strategies in order to reduce the air temperature and save energy. Temperature monitoring in Tehran shows clear evidence of the occurrence of the UHI effect, with a peak in July, where the urban area is circa 6 K warmer than the surrounding areas. The mobile measurements show a park cool island of 6-7 K in 2 central parks, which is also confirmed by satellite images. The effectiveness of three UHI mitigation strategies high albedo material (HAM), greenery on the surface and on the roofs (VEG), and a combination of them (HYBRID) has been studied using simulation with the microscale model ENVI-met. All three strategies show higher cooling effect in the daytime. The average nocturnal cooling effect of VEG and HYBRID (0.92, 1.10 K) is much higher than HAM (0.16 K), although high-density trees show a negative effect on nocturnal cooling.

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Urban heat island intensity and its mitigation strategies in the fast-growing urban area

Journal of Urban Management ◽

10.1016/j.jum.2019.09.004 ◽

2020 ◽

Vol 9 (1) ◽

pp. 54-66 ◽

Cited By ~ 1

Author(s):

Shweta Jain ◽

Srikanta Sannigrahi ◽

Somnath Sen ◽

Sandeep Bhatt ◽

Suman Chakraborti ◽

...

Keyword(s):

Urban Heat Island ◽

Urban Area ◽

Mitigation Strategies ◽

Urban Heat Island Intensity ◽

Heat Island ◽

Fast Growing ◽

Urban Heat

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Modeling nexus of urban heat island mitigation strategies with electricity/power usage and consumer costs: a case study for Phoenix, Arizona, USA

Theoretical and Applied Climatology ◽

10.1007/s00704-016-1985-5 ◽

2016 ◽

Vol 131 (1-2) ◽

pp. 661-669 ◽

Cited By ~ 2

Author(s):

Humberto Silva ◽

Baron S. Fillpot

Keyword(s):

Urban Heat Island ◽

Mitigation Strategies ◽

Heat Island ◽

Electricity Power ◽

Urban Heat

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Spatial Superposition Method via Model Coupling for Urban Heat Island Albedo Mitigation Strategies

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-11-064.1 ◽

2012 ◽

Vol 51 (11) ◽

pp. 1971-1979 ◽

Cited By ~ 2

Author(s):

Humberto Silva ◽

Jay S. Golden

Keyword(s):

Urban Heat Island ◽

Mesoscale Model ◽

Coupled Model ◽

Mitigation Strategies ◽

Turbulence Theory ◽

Superposition Method ◽

Heat Island ◽

Lumped Model ◽

Hourly Temperature ◽

Urban Heat

AbstractA spatial superposition design is presented that couples the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5) with the National Center of Excellence (NCE) lumped urban thermal model for application to the city of Phoenix, Arizona. This technique utilizes an approach similar to Reynolds decomposition from turbulence theory. The presented decomposition takes the NCE model prediction from a mitigated strategy as the mean temperature and the difference between the NCE and MM5 predictions without mitigation strategy as the perturbed temperature. The goal of this coupled model is to provide spatial variability when simulating mitigation strategies for the urban heat island effect, as compared with the spatially invariant lumped model. A validation analysis was performed incorporating a maximum 35% change from the baseline albedo value for the urban environment. It is shown that the coupled model differs by up to 0.39°C with comparable average surface temperature predictions from MM5. The coupled model was also used to perform analysis of three different albedo-driven spatial mitigation schemes. This resulted in the identification that having a lesser number of mitigated points on a square urban grid in Phoenix with the same average albedo leads to a greater reduction in average hourly temperature.

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