The cooling efficiency of urban landscape strategies in a hot dry climate

Shashua‐Bar, Limor; Pearlmutter, David; Erell, Evyatar

doi:10.1016/j.landurbplan.2009.04.005

Cited by 388 publications

(192 citation statements)

References 35 publications

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“…Consequently, land cover strategies will have a different impact on the SEB under different climates. Our results confirm findings of previous studies showing that the spatial context of land cover strategies is important and that planning strategies have to be designed appropriate to the climatic region and to the related urban environment (Shashua-Bar et al, 2009;Gober et al, 2010).…”

Section: Analysis Of Energy Partitioningsupporting

confidence: 90%

Land cover, climate, and the summer surface energy balance in Phoenix, AZ, and Portland, OR

Middel

Brazel

Gober

et al. 2011

Intl Journal of Climatology

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Changes in land use and land cover alter the local energy balance and contribute to distinct urban climates. This paper presents a local-scale above-canopy study of intra-urban land cover mixes in two cities to analyse the relative effects of surface morphology and local climate on the surface energy balance (SEB). The study is conducted for urban areas in Phoenix, Arizona, and Portland, Oregon, cities with distinct climates but similarly warm and dry summers. A Local-Scale Urban Meteorological Parameterization Scheme (LUMPS) is used to analyse the relative contributions of local weather extremes and land cover variations on the urban energy balance. The partitioning of net all-wave radiation into turbulent sensible and latent heat fluxes as well as heat storage is investigated for a typical dry summer month and two extreme weather scenarios in the two cities. Results of sensitivity analyses show that incoming solar radiation is an important driver of the SEB in LUMPS and should be considered in the generation of climate scenarios. The relationship between individual land cover fractions and SEB fluxes is not clear because of interrelated effects of surface characteristics in the land cover mix. Daytime Bowen ratios vary inversely with vegetation fraction between and within cities for all weather scenarios. Impervious surface cover is positively correlated to the available energy that is partitioned into sensible heat. Cumulative evapotranspiration (ET) is similar for average weather conditions across medium wet sites in Phoenix and Portland but varies more in Portland than in Phoenix under extreme weather conditions. Results suggest that land cover manipulation could offset influences of weather extremes on ET in Portland to a certain degree but not in Phoenix. These findings highlight the importance of spatial and climatic context in the urban design process to mitigate the effects of urbanization.

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Section: Analysis Of Energy Partitioningsupporting

confidence: 90%

Land cover, climate, and the summer surface energy balance in Phoenix, AZ, and Portland, OR

Middel

Brazel

Gober

et al. 2011

Intl Journal of Climatology

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“…Once again a small advantage is seen during daytime for the purely vegetative configuration ('trees-grass') compared with 'meshgrass', meaning that the fully 'green' space is the one in which the daytime pedestrian stress is lowest. In this fully vegetated courtyard, air temperature at peak daytime hours was lower than in the bare exposed courtyard by up to 2.5°C (Shashua-Bar et al, 2009). Interestingly, neither the presence of grass nor the presence of trees introduced any significant change in the cooling efficiency Figure 4.…”

Section: Pedestrian Thermal Stressmentioning

confidence: 85%

“…It may also be seen that the vegetative shading treatment ('trees-bare') results in fewer hours of discomfort than 'mesh-bare', owing largely to the high radiative temperatures (45-50°C) of the mesh's bottom surface relative to the underside of tree canopy (which remained close to the courtyard air temperature of up to about 35°C; Figure 3). At the same time, the overhead shading treatments introduced effects which decrease convective heat loss: the trees restricted air flow by up to 80%, and the mesh increased air temperature by up to nearly 1°C (Shashua-Bar et al, 2009).…”

Section: Pedestrian Thermal Stressmentioning

confidence: 99%

The influence of trees and grass on outdoor thermal comfort in a hot‐arid environment

Shashua‐Bar

Pearlmutter

Erell

2011

Intl Journal of Climatology

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381

171

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ABSTRACT:The effects of vegetation on human thermal stress in a hot-arid region were tested in two semi-enclosed urban spaces with various combinations of mature trees, grass, overhead shading mesh and paving. The index of thermal stress was calculated hourly from measured meteorological data in the studied sites to evaluate thermal comfort in the different spaces based on radiative and convective pedestrian-environment energy exchanges and sweat efficiency, and expressed on a thermal sensation scale ranging from 'comfortable' to 'very hot'. The efficiency of water use in providing improved comfort was gauged for each of the vegetative landscaping treatments by comparing the total evapotranspiration with the reduction in thermal stress, both expressed in terms of their values in equivalent energy. While conditions in a paved, unshaded courtyard were found to be uncomfortable throughout the daytime hours (with half of these hours defined by severe discomfort), each of the landscape treatments made a clear contribution to improved thermal comfort. With shading, either by trees or mesh, discomfort was reduced in duration by over half and limited in maximum severity when the shading was placed above paving. When combined with grass, both shading mechanisms yielded comfortable conditions at all hours. In both cases, the effect of trees was more pronounced than that of the mesh, but by a small margin. With unshaded grass, 'hot' conditions in the courtyard were restricted to a short period in mid-afternoon, a considerable improvement over unshaded paving, attributable mainly to the lower radiant surface temperatures.

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“…TVF is defined as the fraction occupied by vegetation canopy of the overlying hemisphere. Therefore, it is suggested that the implementation of grass planting should be combined with trees [96,97]. Shashua-Bar et al [98] compared different combinations of mature trees, grass, overhead shading mesh and paving in a hotarid region.…”

Section: Urban Vegetation Descriptorsmentioning

confidence: 99%

The Impact of Urban Design Descriptors on Outdoor Thermal Environment: A Literature Review

et al. 2017

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This paper presents a literature review on urban design indicators addressing the impact of urban geometry and vegetation on the outdoor thermal environment at the pedestrian level, as urban geometry and vegetation have been regarded as the most influential urban design factors that affect outdoor microclimate. The thermal balance concept is first introduced to elaborate how each component of energy fluxes is affected by the urban built environment, which helps to explore the underlying thermophysical mechanisms of how urban design modifies the outdoor thermal environment. The literature on numerous urban design descriptors addressing urban geometric characteristics is categorized into five groups in this paper according to the design features that the parameters entail, including land use intensity, building form, canyon geometry, space enclosure and descriptive characteristics. The literature on urban vegetation descriptors is reviewed together, followed by the combined effect of urban geometry and vegetation. This paper identifies a series of important urban design parameters and shows that the impact of design parameters on thermal environment varies with time, season, local climate and urban contexts. Contradictory impacts often occur between daytime and nighttime, or different seasons, which requests trade-offs to be achieved when proposing design strategies.

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The cooling efficiency of urban landscape strategies in a hot dry climate

Cited by 388 publications

References 35 publications

Land cover, climate, and the summer surface energy balance in Phoenix, AZ, and Portland, OR

Land cover, climate, and the summer surface energy balance in Phoenix, AZ, and Portland, OR

The influence of trees and grass on outdoor thermal comfort in a hot‐arid environment

The Impact of Urban Design Descriptors on Outdoor Thermal Environment: A Literature Review

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