Realistic Representation of Trees in an Urban Canopy Model

Ryu, Young‐Hee; Bou‐Zeid, Elie; Wang, Zhihua; Smith, James A.

doi:10.1007/s10546-015-0120-y

Cited by 101 publications

(66 citation statements)

References 25 publications

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“…1). Ryu et al (2016) showed that the trees in the urban canyon decreased the sensible heat flux and increased the latent heat flux by roughly a similar amount. Another potential source of uncertainty to this method is the street vegetation composition.…”

Section: Street Vegetationmentioning

confidence: 94%

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A wedge strategy for mitigation of urban warming in future climate scenarios

2017

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Abstract. Heat stress is one of the most severe climate threats to human society in a future warmer world. The situation is further exacerbated in urban areas by urban heat islands (UHIs). Because the majority of world's population is projected to live in cities, there is a pressing need to find effective solutions for the heat stress problem. We use a climate model to investigate the effectiveness of various urban heat mitigation strategies: cool roofs, street vegetation, green roofs, and reflective pavement. Our results show that by adopting highly reflective roofs, almost all the cities in the United States and southern Canada are transformed into "white oases" -cold islands caused by cool roofs at midday, with an average oasis effect of −3.4 K in the summer for the period 2071-2100, which offsets approximately 80 % of the greenhouse gas (GHG) warming projected for the same period under the RCP4.5 scenario. A UHI mitigation wedge consisting of cool roofs, street vegetation, and reflective pavement has the potential to eliminate the daytime UHI plus the GHG warming.

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Section: Street Vegetationmentioning

confidence: 94%

“…1). Second, street vegetation is inherently not identical to its rural counterparts due to the radiative trapping by urban canyons via the "canyon effect" (Wang, 2014;Ryu et al, 2016). Therefore, the same amount of vegetation inside urban canyons may not induce as much cooling as it would in the adjacent rural land. )…”

Section: Street Vegetationmentioning

confidence: 99%

A wedge strategy for mitigation of urban warming in future climate scenarios

2017

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“…With the advances in Light Detecting and Ranging (LiDAR) and unmanned aerial vehicle technology, greenspace patches can be accurately mapped, as well as their vertical dimension (Zhou, 2013). In addition, the two key cooling processes, shading and evapotranspiration, can be measured based on simulation with recent advances in modeling (e.g., Ryu et al, 2016;Song and Wang, 2016;Wang et al, 2016). These advances facilitate future studies that aims to identify such optimal threshold of patch area at which maximum cooling efficiency might occur.…”

Section: Effects Of Patch Size On Shading and Transpirationmentioning

confidence: 99%

Patch size of trees affects its cooling effectiveness: A perspective from shading and transpiration processes

Jiao

Zhou

Zheng

et al. 2017

Agricultural and Forest Meteorology

104

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A B S T R A C TIncreasing urban greenspace, particularly trees, has been widely recognized as an effective means for urban heat mitigation. Lots of uncertainty, however, occurs on how spatial configuration of trees affects their cooling effectiveness. A frequently asked question from urban planners is that whether a large greenspace patch has better cooling effects than several smaller ones, or vice versa. Here, we attempted to address this question by investigating the effects of patch size of trees on the two key cooling processes: shading and transpiration. We chose two typical tree species, Ginkgo biloba and Populus tomentosa, with 4 different patch sizes, and conducted the research in Beijing. We integrated field measurements of air temperature, relative humidity and transpiration rate with model simulation, and conducted the analysis at both the patch and within-patch level. We found: (1) Smaller patches had higher temperature, lower humidity and greater within-patch variations in temperature and humidity than larger ones. (2) With a fixed area of tree cover, a number of small patches can provide more shade than a single large patch, suggesting a monotonic increase of shade provision with the division of a large patch into smaller ones. (3) There was a non-linear relationship between patch size and transpiration rate, suggesting a maximum transpiration rate might occur at certain patch size. By considering the joint effects of shading and transpiration, an optimal size of patch might occur, at which the joint effects of shading and transpiration are maximized.

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“…Krayenhoff et al () represents urban trees within street canyons and above rooftops using a leaf area density profile and parametrizes the associated physical processes for the multi‐layer UCM (Salamanca and Martilli, ). Ryu et al () includes urban tree parametrization in the single‐layer UCM (Kusaka et al , ; Wang et al , ) using a similar representation method commonly used in microscale models. The recent development in the UCMs pursues more realistic representation of the urban vegetation and associated physical processes in a physically interactive parametrization framework.…”

Section: Introductionmentioning

confidence: 99%

Impacts of in‐canyon vegetation and canyon aspect ratio on the thermal environment of street canyons: numerical investigation using a coupled WRF‐VUCM model

Lee

Park

et al. 2016

Quart J Royal Meteoro Soc

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The thermal environment of an urban street canyon in summer becomes a great concern for human health under rapid urbanization. For accurate prediction of the in‐canyon thermal environment, a realistic representation is required of microscale physical processes within the canyon as well as multi‐scale atmospheric interaction between the canopy air and the overlying urban boundary layer. To accomplish this, the Vegetated Urban Canopy Model (VUCM), which interactively parametrizes in‐canyon radiative/dynamic/thermodynamic/hydrological processes based on a combined framework of the two‐dimensional single canyon and the single tree canopy, is implemented into the Weather Research and Forecasting (WRF) model. Using the coupled WRF‐VUCM model, a series of simulations is performed for a hot summer day with a finest grid resolution of 0.333 km to investigate the impacts of in‐canyon vegetation (permeable grass/soil surfaces and trees, with the vegatation fraction fv ranging from 0 to 0.4 which corresponds to 0 to 15% in urban patch area) and canyon aspect ratio (h/w; ranging from 0.5 to 2) on the thermal environment of urban street canyons over the Seoul metropolitan area. The model simulation compares well with the measured 2 m temperatures (above zero‐plane displacement height) and canopy air temperatures at 13 urban sites in Seoul, with root mean square errors of 1.0 and 0.96 °C, respectively. The increase of the in‐canyon vegetation from 0 to 15% (at h/w = 1) leads to a reduction of the canopy air temperature throughout the diurnal cycle, exhibiting relatively larger cooling effect during daytime (∼1.1 °C on average) than at night (∼0.8 °C on average) under a limited condition for evapotranspiration by the in‐canyon vegetation. Provided that the soil moisture is enough for the hydrological effect, the cooling effects significantly increase by a factor of ∼2.5 in both daytime and night‐time. The increase of h/w from 0.5 to 2 (at fv = 0.2) reduces the daytime canopy air temperature (∼1.3 °C on average) but increases the nocturnal canopy air temperature (∼0.3 °C on average). It is also found that the existence of in‐canyon vegetation at h/w > 1 has a synergic cooling benefit to the thermal environment of street canyons compared to the effects of no vegetation. These results demonstrate the importance of interactive parametrization of the physical processes and the interplay of in‐canyon vegetation and building density (via canyon aspect ratio) effects on accurate prediction of the thermal environment of urban street canyons.

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Realistic Representation of Trees in an Urban Canopy Model

Cited by 101 publications

References 25 publications

A wedge strategy for mitigation of urban warming in future climate scenarios

A wedge strategy for mitigation of urban warming in future climate scenarios

Patch size of trees affects its cooling effectiveness: A perspective from shading and transpiration processes

Impacts of in‐canyon vegetation and canyon aspect ratio on the thermal environment of street canyons: numerical investigation using a coupled WRF‐VUCM model

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