The influence of trees and grass on outdoor thermal comfort in a hot-arid environment
01 Aug 2011-International Journal of Climatology (John Wiley & Sons, Ltd.)-Vol. 31, Iss: 10, pp 1498-1506
TL;DR: In this article, 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.
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. Copyright © 2010 Royal Meteorological Society
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Cites background from "The influence of trees and grass on..."
...The shading efficiency in improving the urban microclimate has already been tested by various researchers. shashua-bar et al. (2011) compared an exposed courtyard, which a maximum air temperature of 34 °C in mid-afternoon with a similar courtyard treated a fabric shading mesh. the air temperature…...
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Cites background from "The influence of trees and grass on..."
...Shading is critical for improving human thermal comfort, particularly via reductions in mean radiant temperature which is the dominant influence on outdoor human thermal comfort under warm, sunny conditions [40, 41]....
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References
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TL;DR: The physiological equivalent temperature (PET) is defined as the air temperature at which the heat budget of the human body is balanced with the same core and skin temperature under the complex outdoor conditions to be assessed, and enables a layperson to compare the integral effects of complex thermal conditions outside with his or her own experience indoors.
Abstract: With considerably increased coverage of weather information in the news media in recent years in many countries, there is also more demand for data that are applicable and useful for everyday life. Both the perception of the thermal component of weather as well as the appropriate clothing for thermal comfort result from the integral effects of all meteorological parameters relevant for heat exchange between the body and its environment. Regulatory physiological processes can affect the relative importance of meteorological parameters, e.g. wind velocity becomes more important when the body is sweating. In order to take into account all these factors, it is necessary to use a heat-balance model of the human body. The physiological equivalent temperature (PET) is based on the Munich Energy-balance Model for Individuals (MEMI), which models the thermal conditions of the human body in a physiologically relevant way. PET is defined as the air temperature at which, in a typical indoor setting (without wind and solar radiation), the heat budget of the human body is balanced with the same core and skin temperature as under the complex outdoor conditions to be assessed. This way PET enables a layperson to compare the integral effects of complex thermal conditions outside with his or her own experience indoors. On hot summer days, for example, with direct solar irradiation the PET value may be more than 20 K higher than the air temperature, on a windy day in winter up to 15 K lower.
1,674 citations
"The influence of trees and grass on..." refers methods in this paper
...Computation of thermal stress A variety of models have been used to assess outdoor thermal comfort, often through the use of a hypothetical, ‘physiologically equivalent’ temperature (e.g. Hoppe, 1993, 1999)....
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Book•
14 Jan 2013
TL;DR: In this paper, the authors present a Chronological Sketch of the history of the theory of evaporation and its application in the field of meteorology, including the lower atmosphere and the surface roughness of the Earth's surface.
Abstract: 1. Introduction.- 2. History of the Theories of Evaporation - A Chronological Sketch.- 3. The Lower Atmosphere.- 4. Mean Profiles and Similarity in a Stationary and Horizontally Uniform ABL.- 5. The Surface Roughness Parameterization.- 6. Energy Fluxes at the Earth's Surface.- 7. Advection Effects Near Changes in Surface Conditions.- 8. Methods Based on Turbulence Measurements.- 9. Methods Based on Measurements of Mean Profiles.- 10. Energy Budget and Related Methods.- 11. Mass Budget Methods.- Historical References (Prior to 1900).- References.
1,206 citations
TL;DR: In this article, the thermal effect of covering the building envelope with vegetation on the microclimate in the built environment, for various climates and urban canyon geometries, is discussed.
803 citations
"The influence of trees and grass on..." refers background in this paper
...…ShashuaBar and Hoffman, 2000; Chen and Wong, 2006; Potchter et al., 2006) and of up to 2 K in the case of vegetated surfaces such as urban lawns (Bonan, 2000; SpronkenSmith et al., 2000) and green walls and roofs (e.g. Onmura et al., 2001; Takebayashi and Moriyama, 2007; Alexandri and Jones, 2008)....
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..., 2000) and green walls and roofs (e.g. Onmura et al., 2001; Takebayashi and Moriyama, 2007; Alexandri and Jones, 2008)....
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TL;DR: In this article, the contribution of street design, i.e. aspect ratio (or height-to-width ratio, H / W ) and solar orientation, towards the development of a comfortable microclimate at street level for pedestrians is discussed.
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"The influence of trees and grass on..." refers background or methods in this paper
...Although the measurement of MRT using globe thermometers of varying diameters and materials has received wide attention in recent studies (Ali-Toudert and Mayer, 2006, 2007; Thorsson et al., 2007; Kenny et al., 2008), this approach is still subject to uncertainties given the extreme variability of…...
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...It has been observed repeatedly that due to the dominance of radiation in hot-arid settings, air temperature alone is not necessarily a robust indicator of overall thermal comfort for pedestrians in the urban space (Ali-Toudert and Mayer, 2006; Johansson, 2006; Pearlmutter et al., 2006)....
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TL;DR: The approach to the determination of evaporation varies significantly depending upon the constraints that control the system of interest as discussed by the authors. But, as a result, comprehensive texts on the subject are rare.
Abstract: Evaporation is a topic that crosses several disciplines, and comprehensive texts on the subject are rare. Evaporation Into the Atmosphere is, therefore, a welcome addition to the literature. The approach to the determination of evaporation varies significantly depending upon the constraints that control the system of interest. The oceanographer, for example, is concerned with evaporation from large bodies of water and tends to approach the problem from the aerodynamic or turbulent-diffusion point of view. The hydrologist, on the other hand, is mainly interested in evaporation from the soil and water transpired by plants and may apply the aerodynamic approach to determine evapotranspiration from large homogeneous fields but will be forced to apply the water budget or various degrees of empirism in dealing with long-term losses from heterogeneous basins. Finally, the water-resources engineer concerned with water or energy losses from lakes, reservoirs, or streams, will seldomly apply a purely aerodynamic approach having found that the energy budget, semi-empirical mass transfer, or other approaches best meet his needs.
790 citations
"The influence of trees and grass on..." refers background or methods in this paper
...8, which is typical of values for short-cut grass cited in previous studies (Brutseart, 1982; Pearlmutter et al., 2009)....
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...The grass subsequently planted in the two courtyards was Durban grass with a measured pan evaporation coefficient of approximately 0.8, which is typical of values for short-cut grass cited in previous studies (Brutseart, 1982; Pearlmutter et al., 2009)....
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