Realistic Representation of Trees in an Urban Canopy Model

Young Hee Ryu, Elie R. Bou-Zeid, Zhi Hua Wang, James A. Smith

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

A single-layer urban canopy model that captures sub-facet heterogeneity and various hydrological processes is further developed to explicitly incorporate trees within the urban canyon. The physical processes associated with trees are shortwave/longwave radiation exchange, including mutual interception and shading by trees and buildings and multiple reflections, sensible heat and latent heat (through transpiration) exchange, and root water uptake. A computationally-efficient geometric approach is applied to the radiation exchanges, requiring a priori knowledge of view factors. These view factors are first obtained from independent Monte Carlo ray-tracing simulations, and subsequently simple relations, which are functions of canyon aspect ratio and tree-crown ratio, are proposed to estimate them. The developed model is evaluated against field observations at two urban sites and one suburban site, showing improved performance for latent heat flux compared to the previous version that only includes ground vegetation. The trees in the urban canopy act to considerably decrease sensible heat flux and increase latent heat flux, and these effects are found to be more significant in the more dense urban site. Sensitivity tests are then performed to examine the effects of tree geometry relative to canyon geometry. The results indicate that the tree-crown size relative to canyon width is the most influential parameter to decrease sensible heat flux and increase latent heat flux, resulting in cooling of the urban area.

Original languageEnglish (US)
Pages (from-to)193-220
Number of pages28
JournalBoundary-Layer Meteorology
Volume159
Issue number2
DOIs
StatePublished - May 1 2016

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canopy
canyon
latent heat flux
urban site
sensible heat flux
geometry
water uptake
ray tracing
longwave radiation
shading
interception
transpiration
urban area
cooling
vegetation
simulation
effect

All Science Journal Classification (ASJC) codes

  • Atmospheric Science

Cite this

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abstract = "A single-layer urban canopy model that captures sub-facet heterogeneity and various hydrological processes is further developed to explicitly incorporate trees within the urban canyon. The physical processes associated with trees are shortwave/longwave radiation exchange, including mutual interception and shading by trees and buildings and multiple reflections, sensible heat and latent heat (through transpiration) exchange, and root water uptake. A computationally-efficient geometric approach is applied to the radiation exchanges, requiring a priori knowledge of view factors. These view factors are first obtained from independent Monte Carlo ray-tracing simulations, and subsequently simple relations, which are functions of canyon aspect ratio and tree-crown ratio, are proposed to estimate them. The developed model is evaluated against field observations at two urban sites and one suburban site, showing improved performance for latent heat flux compared to the previous version that only includes ground vegetation. The trees in the urban canopy act to considerably decrease sensible heat flux and increase latent heat flux, and these effects are found to be more significant in the more dense urban site. Sensitivity tests are then performed to examine the effects of tree geometry relative to canyon geometry. The results indicate that the tree-crown size relative to canyon width is the most influential parameter to decrease sensible heat flux and increase latent heat flux, resulting in cooling of the urban area.",
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Realistic Representation of Trees in an Urban Canopy Model. / Ryu, Young Hee; Bou-Zeid, Elie R.; Wang, Zhi Hua; Smith, James A.

In: Boundary-Layer Meteorology, Vol. 159, No. 2, 01.05.2016, p. 193-220.

Research output: Contribution to journalArticle

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