Current World Environment

Introduction

Rural and urban context react differently to processes of momentum transfer (air flow), energy (solar heating) and mass (precipitation). These differences are principles for unique combinations of moisture, thermal, radiative and aerodynamic properties of locations which effects how rural and urban surfaces regulate and partition  existing energy (T. Oke, 1987). In turn, energy partitioning affects the thermal fluxes of these surfaces and of the surrounding layer which they are next to. (Stewart, 2011).

Many features of the physical structure of the city can give impact on the urban climate and negatively results in amplifying urban heat island intensity(T. R. Oke, 1981; P Shahmohamadi et al., 2009).

Heat islands form in urban and suburban areas as many traditional construction materials absorb and restore more of the solar radiation than organic materials in untouched rural areas.

But there are two key factors for this heating. Firstly, most urban building materials are impervious and waterproof, so humidity is not easily accessible to dissipate the sun s energy. Secondly, dark color materials in collaboration with canyon-like structures of urban context trap and collect more of the suns radiative energy (Connors, Galletti, & Chow, 2013; Gartland, 2011; Prashad, 2014; Radhi, Fikry, & Sharples, 2013).

Reducing the surface temperature of roofs may play a key role in improving the thermal condition in cities facing urban heat island (Coutts, Daly, Beringer, & Tapper, 2013; KÅ‚ysik & Fortuniak, 1999; Kolokotsa, Santamouris, & Zerefos, 2013). This goal can be gained by replacement of traditional roof surfaces with green roofs offering much lower temperatures through the summer to enhance their thermal performance and reduce the absorption of solar radiation. This paper investigates the potential of green roofs in ameliorating the negative effects of UHI through the analysis of cooling process by green roofs.

Negative Effects of Heat Islands

UHI has extensive effects on urban context and the infrastructures that support the society (P. Shahmohamadi, Che-Ani, Etessam, Maulud, & Tawil, 2011).  The intensification of an urban heat island has  regional-scale effects on air quality, energy demand and  public health  (Guo, Barnett, & Tong, 2013; Rosenzweig, Solecki, & Slosberg, 2006). UHI phenomenon intensifies the request for energy, speeding up the creation of toxic smog and producing human thermal discomfort and health troubles by increasing heat waves over metropolises (Li, Harvey, & Kendall, 2013; Synnefa, Santamouris, & Apostolakis, 2007).

Summertime UHI significantly reduces the outdoor air quality along with intensifying the energy demand of a city and as a result of this energy intensification, extensive power blackout may happens caused by the increase of the air condition usage. Reports show that thousands of people annually die as a result of heat related diseases. (Davies, Steadman, & Oreszczyn, 2008)., and the latest example is the severe overheat wave was a factor to mortality of about 50, 000 population in Europe, in August 2003. As well as the impact of electricity and temperature consumption, UHI also increases pollutant concentration over cities. Moreover, it effects the local climate by changing wind patterns, forming fog and cloud, increasing humidity, and altering the precipitation rate.” (Mirzaei & Haghighat, 2010)

Both nocturnal and diurnal UHI have a significant effect on the primary and secondary local pollutants in the environment (Sarrat, Lemonsu, Masson, & Guedalia, 2006). They can amplify the pollutant concentrations 10 times higher than the clean atmosphere (Taha, 1997). This phenomenon creates convergence and consequently transfers air pollutants to an urban area and as a result increases respiratory related illnesses in the hot center of an urban area (Lai & Cheng, 2010).

It is obvious that cities with a low climatic quality consume more electricity for cooling the buildings in summer and at the same time for lighting. Furthermore, discomfort and inconvenience for the inhabitants resulting from high temperatures is very usual (Bitan, 1992).

Mitigation Strategies

Neutralizing the impacts of UHI is a main concern for the societies. Because of the problem severity, extensive research work has been done and a large scope of literature is accessible for the subject. The available literature in this field comprises of the concepts, methodologies, latest investigation tools, latest research approaches and mitigation strategies (A. M. Rizwan, L. Y. C. Dennis, & C. Liu, 2008). A number of strategies have been suggested, consolidated and employed with noticeable outcomes (McPherson, 1994; Onishi, Cao, Ito, Shi, & Imura, 2010; A. M. Rizwan, L. Y. Dennis, & C. Liu, 2008; Arthur H Rosenfeld et al., 1995; Arthur H. Rosenfeld, Akbari, Romm, & Pomerantz, 1998; Mat Santamouris, Synnefa, & Karlessi, 2011; M. F. Shahidan, Jones, Gwilliam, & Salleh, 2012; Solecki et al., 2005; Takebayashi & Moriyama, 2007; N. H. Wong & Yu, 2005).  Offered mitigation strategies and techniques include the use of green roofs (Alexandri & Jones, 2008; Bass, Krayenhoff, Martilli, Stull, & Auld, 2003; Bass, Krayenhoff, Martilli, & Stull, 2002; Kolokotsa et al., 2013; M Santamouris, 2012; Susca, Gaffin, & Dell Osso, 2011; Takebayashi & Moriyama, 2007; J. K. W. Wong & Lau, 2013), the use of greenery system in the urban context including proper landscaping and design of green modules (M Santamouris, 2013; Yu & Hien, 2009; Zoulia, Santamouris, & Dimoudi, 2009), proper shading and radiation control of surfaces (Akbari, Pomerantz, & Taha, 2001), using cool roofs (Berdahl & Bretz, 1997; Bretz, Akbari, & Rosenfeld, 1998; Prado & Ferreira, 2005; Arthur H. Rosenfeld et al., 1998; Synnefa, Dandou, Santamouris, Tombrou, & Soulakellis, 2008; Synnefa et al., 2007; Takebayashi & Moriyama, 2007), mitigating of anthropogenic heat (Ichinose, Shimodozono, & Hanaki, 1999; Sailor, 2011) , Increasing the albedo of construction  materials (Li, Harvey, Holland, & Kayhanian, 2013), and increasing wind velocity in order to alleviate the UHI impact in cities.

The impact of roofs on the intensification of UHI is very critical. Many researches have proven that roof surfaces are a main factor in the thermal balance of a city (Akbari, Shea Rose, & Taha, 2003; Arnfield, 1982; Bansal, Garg, & Kothari, 1992; KÅ‚ysik & Fortuniak, 1999; Susca et al., 2011). Roofs include a noticeable percentage of the urban area and participate extremely to the intensification of UHI. Roofs include almost 20 to 25% of the urban surface (Akbari et al., 2003; Susca et al., 2011) and conventional roof materials tend to heat up in the sun to temperatures of 50–90°C. By heating roof materials some problems are created for the buildings below them such as: uprising indoor temperature, increasing energy demand for cooling, reduced indoor thermal comfort, more expenditure on utility bills, rapid corrosion of the roof materials, more deterioration on cooling systems.

Moreover hot roofs are the source of problems for their communities like increasing electricity demand particularly in summer, more probability for electrical shutdown, increasing the rate of emissions in power plants, warmer suburban and urban temperatures, aiding smog formation because of the temperature and emission combination and sending more roof materials waste sent to landfill(Gartland, 2011). Reducing the surface temperature of roofs may play a key role in improving the thermal condition in cities facing urban heat island. This goal can be gained by replacement of traditional roof surfaces with green roofs offering much lower temperatures through the summer to enhance their thermal performance and reduce the absorption of solar radiation.

Roofs and their Effect on Urban Climate

The portion of solar radiation reflected by the exterior features of a construction extensively impacts the total heat gain or loss of the construction. This is especially true for areas that are exposed to a large amount of solar radiation (Reagan & Acklam, 1979). One of these elements is roof. Roofs cover between 20 to 25 percent of urban area and they are the hottest elements seen in thermal images of urban areas. As a matter of fact, most conventional roofing materials usually reach temperatures between 65–90ºC. Their solar reflectance extends between five and 25 percent which means they absorb 75–95 percent of the sun s radiative energy. The widespread use of traditional roofing materials in urban areas intensifies the amount of solar radiation collected by urban context. Conventional roofing materials also have other characteristics that deteriorate the heat island problem. Heat capacity and thermal conductivity are also critical issues. Traditional roofing materials tend to store more heat throughout the day, and dissipate it gradually at night.(Gartland, 2011). They emit the heat through infrared radiation and as well transfer it by convection to the volumetric air which surrounded them and exacerbate the UHI effect. As well, they conduct a part of the stored heat to the buildings below and disturb the thermal comfort of inhabitants and make them to spend more electricity for air-conditioning. As a consequence, the buildings emit more heat from air-conditioning process directly and power plants emission indirectly. Besides, the materials in traditional roofing systems are impermeable which turn them to solid elements that prevent water from penetration and latent heat evaporation process. Once latent heat phenomenon is involved, evaporation or sometimes condensation also impacts the thermal system of the roof surfaces (M Santamouris, 2013).

The Process of UHI Mitigation by Using Green Roofs

Plants are one of the essential elements for a healthy city. Greenery system provides enormous benefits to an urban area which includes less energy demand, pollutant reduction, run-off water management and better ecosystem (Arabi, 2014; Gartland, 2011) . But above all, vegetation mitigates the urban heat island effect through three processes ((Akbari & Rose, 2001, 18; Emmanuel, 2005, 1600; Huang, Akbari, & Taha, 1990; Arthur H Rosenfeld et al., 1995, 256; M Santamouris et al., 2001, 214; M. Shahidan, 2011, 168; Shashua-Bar & Hoffman, 2000, 227; Solecki et al., 2005, 39). Firstly, plants shade the buildings and protect them against solar radiation. As a result the building below them will be cooler. They reduce the heat convection to the air above, mitigate UHI and as a consequence decrease the energy for cooling. The rate of solar radiation transferred under the canopy of plants depends on plant type. But, it s usually between 6 to 30 percent in summer and 10 to 80 percent in winter (M. F. Shahidan et al., 2012). Moreover, the plants with high density canopy that produce lower quantities of radiant heat will lead to the minimum quantities of soil radiation below the plant canopy. This situation improves evapotranspiration and the generation of extra latent heat supports the air temperature mitigation process and relative humidity enrichment. Reduction in air warming results in cooling benefits by creation of high quality shade and filtering the solar radiation (M. F. Shahidan et al., 2012). Shading plants also make people feel cooler and more comfortable. Besides, they reduce the risk of heart attack and keep the people safe from the sun s dangerous ultraviolet rays. Secondly, during the photosynthesis process, vegetation converts water, carbon dioxide and solar radiation to glucose and oxygen. For this conversion, plants use an auxiliary process named evapotranspiration to keep themselves cool (Kalogirou, 2009). Plants absorb water through their roots and release it into the air in the form of vapor through their leaves (Monteith, 1965). They use the energy of solar radiation to evaporate water and as a consequence the energy consumed for evaporation is not used to increase the air temperature. It is calculated that an average tree evaporates 1460kg of water  during a clear summer day and consumes almost 860MJ of energy; this outdoor cooling effect is equivalent to five typical air conditioners (Che-Ani et al., 2009; Matheos Santamouris & Asimakopoulos, 2001). As a result, air temperature is lower within and downwind of well-vegetated regions because of evapotranspiration.

In overall, different studies (Huang et al., 1990, 7; Kurn, Bretz, Huang, & Akbari, 1994, 23) proves that peak temperatures in well vegetated areas are cooler than those in bare lands.

Thirdly, plants and greenery system can also be used as wind shield. This effect is useful throughout the cold seasons (Gartland, 2011). Experiments show that vegetation decrease wind velocity by 20–80 per cent, according to the canopy density (Huang et al., 1990). On the other hand, it s useful in summer too. With positioning vegetation on roofs, cooling energy needed to cool buildings will reduce and this is because the building is protected against sun radiations and reflected radiations of environment (Akbari, 2002, 119; Brown & Gillespie, 1995, 9; Robinette, 1972, 131; N. Wong et al., 2007, 2949; Yu & Hien, 2006, 118).

In total, most of the existing and recent studies (table below) conclude that green roofs have a strong effect in mitigation UHI and improving urban climate.

Table 1A: Summary of existing studies about the effect of green roofs on urban heat island

Conclusion

The urban environment is deteriorating annually and urban heat island phenomenon is amplifying in parallel. Increased temperature, high pollution, health problems are the negative effects of UHI. In order to ameliorate these negative effects, some strategies can be employed. One of them is the implementation of green roofs. Green roofs can be used as a multi-purpose strategy that mitigate heat island and compensate the shortage of green spaces simultaneously. Moreover, this technique leads to more positive effects such as mitigating air pollution, management of run-off water, improving public health and aesthetic aspects of an urban context. By using green roofs, the hottest spots of a city convert to the coolest ones. In a nutshell, using green roofs as a UHI mitigation strategy has the following benefits:

Reduction in cooling and heating energy demand, relying on the type of green roof, building size and climatic condition.

Apart from absorbing heat, reducing the tendency towards thermal movement of air, a green roof act as a wind buffer and filters the air moving through it;

During the photosynthesis process, greenery system converts water, carbon dioxide and sun radiation to glucose and oxygen. This cyclic process provides humans and animals food and oxygen and;

Through the evapotranspiration process plants absorb water through their roots and release it into the air in the form of vapor through their leaves. They use the energy of sun radiation to evaporate water and as a consequence the energy consumed for evaporation isn t used for increasing the air temperature.

Vegetation decrease wind velocity by 20–80 per cent, according to the canopy density and as a consequence cooling energy needed to cool buildings will reduce and this is because the building is protected against sun radiations and reflected radiations of environment. The studies investigated in this paper prove that the cooling and mitigation ability of green roofs is very important and can vastly participate in decreasing temperature in urban context. Thus, this paper recommends using green roofs not only for decreasing the harmful impacts of heat island but also for compensating the shortage of greenery system, pollutant reduction, management of run-off water and public health.

Acknowledgement

This paper was supported by Universiti Putra Malaysia

References

1. Akbari, H. (2002). Shade trees reduce building energy use and CO< sub> 2 emissions from power plants. Environmental Pollution, 116, S119-S126.
2. Akbari, H., Pomerantz, M., & Taha, H. (2001). Cool surfaces and shade trees to reduce energy use and improve air quality in urban areas. Solar Energy, 70(3), 295-310.
3. Akbari, H., & Rose, L. S. (2001). Characterizing the fabric of the urban environment: a case study of Salt Lake City, Utah. Lawrence Berkeley National Laboratory Report No. LBNL-47851, Berkeley, CA.
4. Akbari, H., Shea Rose, L., & Taha, H. (2003). Analyzing the land cover of an urban environment using high-resolution orthophotos. Landscape and Urban Planning, 63(1), 1-14. doi: http://dx.doi.org/10.1016/S0169-2046(02)00165-2
5. Alexandri, E., & Jones, P. (2008). Temperature decreases in an urban canyon due to green walls and green roofs in diverse climates. Building and Environment, 43(4), 480-493.
6. Arabi, R. S., Amir; Khodabakhshi, Sahar. (2014). Benefits of green roofs; a review paper. [Review paper]. Elixir International Journal, 68, 22222-22228.
7. Arnfield, A. J. (1982). An approach to the estimation of the surface radiative properties and radiation budgets of cities. Physical Geography, 3(2), 97-122.
8. Bansal, N. K., Garg, S. N., & Kothari, S. (1992). Effect of exterior surface colour on the thermal performance of buildings. Building and Environment, 27(1), 31-37. doi: http://dx.doi.org/10.1016/0360-1323(92)90005-A
9. Bass, B., Krayenhoff, E. S., Martilli, A., Stull, R. B., & Auld, H. (2003). The impact of green roofs on Toronto s urban heat island. Proceedings of Greening Rooftops for Sustainable Communities.
10. Bass, B., Krayenhoff, S., Martilli, A., & Stull, R. (2002). Mitigating the urban heat island with green roof infrastructure. Urban Heat Island Summit: Toronto.
11. Berdahl, P., & Bretz, S. E. (1997). Preliminary survey of the solar reflectance of cool roofing materials. Energy and Buildings, 25(2), 149-158. doi: http://dx.doi.org/10.1016/S0378-7788(96)01004-3
12. Bitan, A. (1992). The high climatic quality city of the future. Atmospheric Environment. Part B. Urban Atmosphere, 26(3), 313-329.
13. Bretz, S., Akbari, H., & Rosenfeld, A. (1998). Practical issues for using solar-reflective materials to mitigate urban heat islands. Atmospheric Environment, 32(1), 95-101. doi: http://dx.doi.org/10.1016/S1352-2310(97)00182-9
14. Brown, R. D., & Gillespie, T. J. (1995). Microclimatic landscape design: creating thermal comfort and energy efficiency: John Wiley & Sons.
15. Castleton, H. F., Stovin, V., Beck, S. B. M., & Davison, J. B. (2010). Green roofs; building energy savings and the potential for retrofit. Energy and Buildings, 42(10), 1582-1591. doi: http://dx.doi.org/10.1016/j.enbuild.2010.05.004
16. Che-Ani, A., Shahmohamadi, P., Sairi, A., Mohd-Nor, M., Zain, M., & Surat, M. (2009). Mitigating the urban heat island effect: Some points without altering existing city planning. European Journal of Scientific Research, 35(2), 204-216.
17. Chen, H., Ooka, R., Huang, H., & Tsuchiya, T. (2009). Study on mitigation measures for outdoor thermal environment on present urban blocks in Tokyo using coupled simulation. Building and Environment, 44(11), 2290-2299. doi: http://dx.doi.org/10.1016/j.buildenv.2009.03.012
18. Connors, J. P., Galletti, C. S., & Chow, W. T. (2013). Landscape configuration and urban heat island effects: assessing the relationship between landscape characteristics and land surface temperature in Phoenix, Arizona. Landscape ecology, 28(2), 271-283.
19. Coutts, A. M., Daly, E., Beringer, J., & Tapper, N. J. (2013). Assessing practical measures to reduce urban heat: Green and cool roofs. Building and Environment, 70, 266-276.
20. Davies, M., Steadman, P., & Oreszczyn, T. (2008). Strategies for the modification of the urban climate and the consequent impact on building energy use. Energy Policy, 36(12), 4548-4551. doi: 10.1016/j.enpol.2008.09.013
21. Emmanuel, R. (2005). Thermal comfort implications of urbanization in a warm-humid city: the Colombo Metropolitan Region (CMR), Sri Lanka. Building and Environment, 40(12), 1591-1601.
22. Gartland, L. (2011). Heat islands: understanding and mitigating heat in urban areas: Routledge.
23. Guo, Y., Barnett, A. G., & Tong, S. (2013). Spatiotemporal model or time series model for assessing city-wide temperature effects on mortality? Environmental Research, 120(0), 55-62. doi: http://dx.doi.org/10.1016/j.envres.2012.09.001
24. Harazono, Y., Teraoka, S., Nakase, I., & Ikeda, H. (1990). Effects of rooftop vegetation using artificial substrates on the urban climate and the thermal load of buildings. Energy and Buildings, 15(3–4), 435-442. doi: http://dx.doi.org/10.1016/0378-7788(90)90018-E
25. Huang, Y., Akbari, H., & Taha, H. (1990). The wind-shielding and shading effects of trees on residential heating and cooling requirements: Lawrence Berkeley Lab., CA (USA).
26. Hui, S. (2009). Study of Thermal and Energy Performance of Green Roof Systems: Final Report. Department of Mechanical Engineering, The University of Hong Kong, Hong Kong.
27. Ichinose, T., Shimodozono, K., & Hanaki, K. (1999). Impact of anthropogenic heat on urban climate in Tokyo. Atmospheric Environment, 33(24–25), 3897-3909. doi: http://dx.doi.org/10.1016/S1352-2310(99)00132-6
28. Kalogirou, S. A. (2009). Solar energy engineering: processes and systems: Academic Press.
29. KÅ‚ysik, K., & Fortuniak, K. (1999). Temporal and spatial characteristics of the urban heat island of Łódź, Poland. Atmospheric Environment, 33(24), 3885-3895.
30. Kolokotsa, D., Santamouris, M., & Zerefos, S. (2013). Green and cool roofs urban heat island mitigation potential in European climates for office buildings under free floating conditions. Solar Energy, 95, 118-130.
31. Lai, L. W., & Cheng, W. L. (2010). Urban heat island and air pollution--an emerging role for hospital respiratory admissions in an urban area. Journal of environmental health, 72(6), 32.
32. Li, H., Harvey, J., Holland, T., & Kayhanian, M. (2013). The use of reflective and permeable pavements as a potential practice for heat island mitigation and stormwater management. Environmental Research Letters, 8(1), 015023.
33. Li, H., Harvey, J., & Kendall, A. (2013). Field measurement of albedo for different land cover materials and effects on thermal performance. Building and Environment, 59, 536-546.
34. McPherson, E. G. (1994). Cooling urban heat islands with sustainable landscapes. The ecological city: preserving and restoring urban biodiversity. University of Massachusetts Press, Amherst, 151-171.
35. Mirzaei, P. A., & Haghighat, F. (2010). Approaches to study urban heat island–abilities and limitations. Building and Environment, 45(10), 2192-2201.
36. Monteith, J. (1965). Evaporation and environment. Paper presented at the Symp. Soc. Exp. Biol.
37. Oke, T. (1987). Boundary Layer Climates (2nd edn.) Methuen. Co. Ltd.: London, 435.
38. Oke, T. R. (1981). Canyon geometry and the nocturnal urban heat island: comparison of scale model and field observations. Journal of Climatology, 1(3), 237-254.
39. Onishi, A., Cao, X., Ito, T., Shi, F., & Imura, H. (2010). Evaluating the potential for urban heat-island mitigation by greening parking lots. Urban forestry & Urban greening, 9(4), 323-332.
40. Pompeii II, W. C. (2010). Assessing Urban Heat Island Mitigation using Green Roofs: A Hardware Scale Modeling Approach. SHIPPENSBURG UNIVERSITY.
41. Prado, R. T. A., & Ferreira, F. L. (2005). Measurement of albedo and analysis of its influence the surface temperature of building roof materials. Energy and Buildings, 37(4), 295-300. doi: http://dx.doi.org/10.1016/j.enbuild.2004.03.009
42. Prashad, L. (2014). Urban Heat Island. Encyclopedia of Remote Sensing, 878-881.
43. Radhi, H., Fikry, F., & Sharples, S. (2013). Impacts of urbanisation on the thermal behaviour of new built up environments: A scoping study of the urban heat island in Bahrain. Landscape and Urban Planning, 113, 47-61.
44. Reagan, J., & Acklam, D. (1979). Solar reflectivity of common building materials and its influence on the roof heat gain of typical southwestern USA residences. Energy and Buildings, 2(3), 237-248.
45. Rizwan, A. M., Dennis, L. Y., & Liu, C. (2008). A review on the generation, determination and mitigation of Urban Heat Island. Journal of Environmental Sciences, 20(1), 120-128.
46. Rizwan, A. M., Dennis, L. Y. C., & Liu, C. (2008). A review on the generation, determination and mitigation of Urban Heat Island. Journal of Environmental Sciences, 20(1), 120-128. doi: http://dx.doi.org/10.1016/S1001-0742(08)60019-4
47. Robinette, G. O. (1972). Plants, people, and environmental quality: A study of plants and their environmental functions (Vol. 4): US Department of the Interior, National Park Service.
48. Rosenfeld, A. H., Akbari, H., Bretz, S., Fishman, B. L., Kurn, D. M., Sailor, D., & Taha, H. (1995). Mitigation of urban heat islands: materials, utility programs, updates. Energy and Buildings, 22(3), 255-265.
49. Rosenfeld, A. H., Akbari, H., Romm, J. J., & Pomerantz, M. (1998). Cool communities: strategies for heat island mitigation and smog reduction. Energy and Buildings, 28(1), 51-62. doi: http://dx.doi.org/10.1016/S0378-7788(97)00063-7
50. Rosenzweig, C., Solecki, W., & Slosberg, R. (2006). Mitigating New York Citys heat island with urban forestry, living roofs, and light surfaces. A report to the New York State Energy Research and Development Authority.
51. Sailor, D. J. (2011). A review of methods for estimating anthropogenic heat and moisture emissions in the urban environment. International Journal of Climatology, 31(2), 189-199. doi: 10.1002/joc.2106
52. Santamouris, M. (2012). Cooling the cities–a review of reflective and green roof mitigation technologies to fight heat island and improve comfort in urban environments. Solar Energy.
53. Santamouris, M. (2013). Using cool pavements as a mitigation strategy to fight urban heat island—A review of the actual developments. Renewable and Sustainable Energy Reviews, 26, 224-240.
54. Santamouris, M., & Asimakopoulos, D. D. N. (2001). Energy and climate in the urban built environment: Routledge.
55. Santamouris, M., Papanikolaou, N., Livada, I., Koronakis, I., Georgakis, C., Argiriou, A., & Assimakopoulos, D. (2001). On the impact of urban climate on the energy consumption of buildings. Solar Energy, 70(3), 201-216.
56. Santamouris, M., Synnefa, A., & Karlessi, T. (2011). Using advanced cool materials in the urban built environment to mitigate heat islands and improve thermal comfort conditions. Solar Energy, 85(12), 3085-3102.
57. Sarrat, C., Lemonsu, A., Masson, V., & Guedalia, D. (2006). Impact of urban heat island on regional atmospheric pollution. Atmospheric Environment, 40(10), 1743-1758. doi: 10.1016/j.atmosenv.2005.11.037
58. Scherba, A., Sailor, D. J., Rosenstiel, T. N., & Wamser, C. C. (2011). Modeling impacts of roof reflectivity, integrated photovoltaic panels and green roof systems on sensible heat flux into the urban environment. Building and Environment, 46(12), 2542-2551. doi: http://dx.doi.org/10.1016/j.buildenv.2011.06.012
59. Shahidan, M. (2011). The potential optimum cooling effect of vegetation with ground surface physical properties modification in mitigating the urban heat island effect in Malaysia. Cardiff University.
60. Shahidan, M. F., Jones, P. J., Gwilliam, J., & Salleh, E. (2012). An evaluation of outdoor and building environment cooling achieved through combination modification of trees with ground materials. Building and Environment.
61. Shahmohamadi, P., Ani, A., Abdullah, N., Maulud, K., Tahir, M., & Nor, M. (2009). The Conceptual Framework on Formation of Urban Heat Island in Tehran Metropolitan, Iran: A Focus on Urbanization Factor. European Journal of Scientific Research.
62. Shahmohamadi, P., Che-Ani, A., Etessam, I., Maulud, K., & Tawil, N. (2011). Healthy Environment: The Need to Mitigate Urban Heat Island Effects on Human Health. Procedia Engineering, 20, 61-70.
63. Shashua-Bar, L., & Hoffman, M. (2000). Vegetation as a climatic component in the design of an urban street: An empirical model for predicting the cooling effect of urban green areas with trees. Energy and Buildings, 31(3), 221-235.
64. Smith, K. R., & Roebber, P. J. (2011). Green roof mitigation potential for a proxy future climate scenario in Chicago, Illinois. Journal of Applied Meteorology and Climatology, 50(3), 507-522.
65. Solecki, W. D., Rosenzweig, C., Parshall, L., Pope, G., Clark, M., Cox, J., & Wiencke, M. (2005). Mitigation of the heat island effect in urban New Jersey. Global Environmental Change Part B: Environmental Hazards, 6(1), 39-49. doi: http://dx.doi.org/10.1016/j.hazards.2004.12.002
66. Stewart, I. D. (2011). Redefining the urban heat island.
67. Sun, C. Y., Lee, K. P., Lin, T. P., & Lee, S. H. (2012). Vegetation as a Material of Roof and City to cool down the temperature. Advanced Materials Research, 461, 552-556.
68. Susca, T., Gaffin, S., & Dell Osso, G. (2011). Positive effects of vegetation: Urban heat island and green roofs. Environmental Pollution, 159(8), 2119-2126.
69. Synnefa, A., Dandou, A., Santamouris, M., Tombrou, M., & Soulakellis, N. (2008). On the Use of Cool Materials as a Heat Island Mitigation Strategy. Journal of Applied Meteorology and Climatology, 47(11), 2846-2856. doi: 10.1175/2008jamc1830.1
70. Synnefa, A., Santamouris, M., & Apostolakis, K. (2007). On the development, optical properties and thermal performance of cool colored coatings for the urban environment. Solar Energy, 81(4), 488-497. doi: http://dx.doi.org/10.1016/j.solener.2006.08.005
71. Taha, H. (1997). Urban climates and heat islands: albedo, evapotranspiration, and anthropogenic heat. Energy and Buildings, 25(2), 99-103.
72. Takebayashi, H., & Moriyama, M. (2007). Surface heat budget on green roof and high reflection roof for mitigation of urban heat island. Building and Environment, 42(8), 2971-2979.
73. Wong, J. K. W., & Lau, L. S.-K. (2013). From the urban heat island to the green island? A preliminary investigation into the potential of retrofitting green roofs in Mongkok district of Hong Kong. Habitat International, 39, 25-35.
74. Wong, N., Kardinal Jusuf, S., Aung La Win, A., Kyaw Thu, H., Syatia Negara, T., & Xuchao, W. (2007). Environmental study of the impact of greenery in an institutional campus in the tropics. Building and Environment, 42(8), 2949-2970.
75. Wong, N. H., Kardinal Jusuf, S., Aung La Win, A., Kyaw Thu, H., Syatia Negara, T., & Xuchao, W. (2007). Environmental study of the impact of greenery in an institutional campus in the tropics. Building and Environment, 42(8), 2949-2970. doi: http://dx.doi.org/10.1016/j.buildenv.2006.06.004
76. Wong, N. H., & Yu, C. (2005). Study of green areas and urban heat island in a tropical city. Habitat International, 29(3), 547-558.
77. Yu, C., & Hien, W. N. (2006). Thermal benefits of city parks. Energy and Buildings, 38(2), 105-120.
78. Yu, C., & Hien, W. N. (2009). Thermal impact of strategic landscaping in cities: A review. Advances in Building Energy Research, 3(1), 237-260.
79. Zoulia, I., Santamouris, M., & Dimoudi, A. (2009). Monitoring the effect of urban green areas on the heat island in Athens. Environmental monitoring and assessment, 156(1-4), 275-292.