Effects of green roofs’ variations on the regional thermal environment using measurements and simulations in Chongqing, China

Jin, Chaoqiang; Bai, Xian–Xu; Luo, Te; Zhang, Min

doi:10.1016/j.ufug.2017.12.002

Cited by 57 publications

(32 citation statements)

References 48 publications

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“…Meanwhile, the increase of urban density restrains the pedestrian cooling performances, and green roofs play an insignificant role in medium- and high-density neighborhoods [21,24,26]. It is also evidenced that building layout and associated green roof arrangement can affect the cooling performance of green roof [27,28]. For instance, among idealized enclosing-, scattered-, and array-shaped neighborhoods, green roofs with enclosing layout had the best cooling performance, followed by the array layout, and the scattered layout [28].…”

Section: Introductionmentioning

confidence: 99%

Impact of Morphological Characteristics of Green Roofs on Pedestrian Cooling in Subtropical Climates

Zhang

Zhu

et al. 2019

IJERPH

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Growing and densifying cities set a challenge for preserving and enhancing green spaces to cool urban spaces. Green roofs, involving the planting of vegetation on rooftops, are regarded as an alternative approach to enhancing urban greenery and urban cooling. For better cooling performances, it is essential to reasonably configure green roofs, especially in real and complex neighborhoods. Therefore, the aim of this paper is to investigate the impact of morphological characteristics of green roofs on pedestrian cooling in real and complex neighborhoods. In specific, based on an ENVI-met model, we studied the effect of greening layout, coverage ratio, vegetation height, and building height on pedestrian air temperature reduction in the tropical city of Hangzhou, China. Results indicate green roofs could generate moderate effects on pedestrian air temperature reduction (around 0.10–0.30 °C), while achieving a cooling performance of 0.82 °C. Green roofs in upwind zones were able to generate the most favorable cooling performance, while green roofs in downwind zones made slight differences to pedestrian thermal environments. Green roofs with a low coverage ratio were not useful for lowering pedestrian temperature, and a greening coverage ratio of 25–75% in upwind zones was cost-effective in real neighborhoods. Locations that were horizontally close to green roofs enjoyed better cooling performances. Increasing vegetation height could strengthen cooling effects of green roofs, while an increase in building height weakened the cooling performance. Nevertheless, higher building height could enhance pedestrian cooling performances because of building shading effects. In addition, because of wind effects and building shading, building height limits for the cooling performance of green roofs could be higher than 60 m.

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Section: Introductionmentioning

confidence: 99%

Impact of Morphological Characteristics of Green Roofs on Pedestrian Cooling in Subtropical Climates

Zhang

Zhu

et al. 2019

IJERPH

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“…Furthermore, no obvious linear relationship is observed between 50% and 100% of green roofs in the three LCZs. It is noticeable that the Ta drop of green roof on the pedestrian height in this study is quite insignificant compared to the very few relevant studies [87]. The reason may be attributed to the improper physical characteristics of the green roof setting in the simulation, such as leaf area index, plant height, and soil thickness [88].…”

Section: Discussionmentioning

confidence: 58%

“…A previous study shows that the green roof strategy can effectively reduce the temperature of the outer surface of the roof and help reduce the building energy consumption [85]. However, the cooling impacts of the green roofs on sidewalks at pedestrian height depend on the building height [86,87]. Furthermore, no obvious linear relationship is observed between 50% and 100% of green roofs in the three LCZs.…”

Section: Discussionmentioning

confidence: 93%

Numerical Simulation of Local Climate Zone Cooling Achieved through Modification of Trees, Albedo and Green Roofs—A Case Study of Changsha, China

Chen

Zheng

2020

Sustainability

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By exploring the cooling potential of tree quantity, ground albedo, green roofs and their combinations in local climate zone (LCZ)-4, LCZ-5, and LCZ-6, this study focuses on the optimum cooling level that can be achieved in open residential regions in Changsha. It designs and models 39 scenarios by integrating in situ measurement and ENVI-met numerical simulation and further compares cooling effects of various combinations of the cooling factors. The results show that (1) an increased number of trees and higher albedo are more effective compared to green roofs in reducing summer potential temperatures at street level (2 m high) in three LCZs. Negative correlations are observed in the pedestrian air temperature with trees and ground albedo; (2) the effects of cooling factors vary among different LCZ classes, with the increased 60% more trees leading to lower outdoor temperatures for LCZ-4 (0.28 °C), LCZ-5 (0.39 °C), and LCZ-6 (0.54 °C), while higher albedo of asphalt surface (increased by 0.4) is more effective in LCZ-4 (reaches to 0.68 °C) 14:00, compare to LCZ-5 (0.49 °C) and LCZ-6 (0.38 °C); (3) applying combined cooling methods can provoke air temperature reduction (up to 0.96 °C), especially when higher levels of tree quantities (increased by 60%) are coupled with cool ground materials (albedo increased by 0.4). The results can contribute useful information for improving thermal environment in existing residential regions and future residential planning.

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“…Similar simulation results have been also reported by Ng et al [135], who investigated the cooling potential of grass-planted roofs applied in high-rise buildings in Hong Kong, China. The analysis indicated a low decrease of the ambient T air at the street level that does not exceed 0.12 • C. Finally, Jin et al [136] have applied both measurement and simulation methods to investigate the effect of intensive and extensive roof types on the thermal environment of both mid-rise and high-rise areas in Chongqing, China. The obtained results suggested that the intensive and extensive roof types can lead to a reduction of the peak T air close to 0.40 • C and 0.30 • C, respectively, in the mid-rise area, while negligible differences have been noticed in the high-rise area for both roof types.…”

Section: Adding Green Roofsmentioning

confidence: 99%

“…-For the green roof with soil depth = 15cm and LAI = 2, a peak cooling effect at the human level of 0.4 • C and 1.1 • C, at noon and midnight, respectively -For the green roof with soil depth = 15cm and LAI = 1, peak cooling effect at the human level of 0.2 • C and 0.7 • C at noon and midnight, respectively -Negligible impact of green roofs on T mrt at the human level [131] Apply intensive and extensive types of roofs in low and high (HR)-rise areas in Hong Kong, China -In LR areas: maximum T air reduction by 0.7 • C and 1.7 • C due to extensive and intensive green roof types, respectively -In HR areas: maximum T air reduction by 0.4 • C and 0.8 • C due to extensive and intensive green roof types, respectively [136] Apply extensive and intensive types, LAI = 4.6 in several mid and high-rise urban areas in Chongqing, China -In the mid-rise area: maximum T air reduction of 0.3 • C and 0.4 • C due to the extensive and intensive roof types, respectively -In the high-rise area: negligible T air reduction both for the intensive and the extensive case [132] Add extensive and intensive roof types in buildings of generic high, medium and low-density areas, under four different climatic conditions (Hong Kong, Cairo, Tokyo, Paris) -Maximum T air reduction between 0.05-0.6 • C, depending on the roof type, climate and urban density -Low cooling effect in high rise areas, for all the examined climatic conditions [133] Add extensive green roofs covered by grass with a LAD of 0.3 m 2 /m 3 in all roofs of a dense urban block in Munich, Germany Negligible T air reduction and minor changes on thermal comfort indices…”

Section: Refmentioning

confidence: 99%

Urban Warming and Cities’ Microclimates: Investigation Methods and Mitigation Strategies—A Review

et al. 2020

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The increased rates of urbanization and industrialization of the 20th and 21st centuries have dramatically changed the land use and cover of modern cities, contributing to the degradation of the urban microclimate and the rise of the ambient urban air temperatures. Given the multiple negative energy, environmental and social consequences of urban warming, the present paper summarizes the findings of previous studies, assessing the main causes of the phenomenon along with the key investigation methods involving experimental and computational approaches. There follows a description of the most common mitigations, and adaption strategies towards the attenuation of urban warming are described. The analyzed elements include the addition of green spaces such as trees, grass and green roofs; changes on the albedo of the urban surfaces and water-based techniques, as well as a combination of them. The discussion of the reported findings in the existing literature clearly reflects the impact of urban morphology on the outdoor thermal environment, providing also useful information for professionals and urban planners involved at the phase of decision-making.

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Effects of green roofs’ variations on the regional thermal environment using measurements and simulations in Chongqing, China

Cited by 57 publications

References 48 publications

Impact of Morphological Characteristics of Green Roofs on Pedestrian Cooling in Subtropical Climates

Impact of Morphological Characteristics of Green Roofs on Pedestrian Cooling in Subtropical Climates

Numerical Simulation of Local Climate Zone Cooling Achieved through Modification of Trees, Albedo and Green Roofs—A Case Study of Changsha, China

Urban Warming and Cities’ Microclimates: Investigation Methods and Mitigation Strategies—A Review

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