期刊
BOUNDARY-LAYER METEOROLOGY
卷 159, 期 2, 页码 193-220出版社
SPRINGER
DOI: 10.1007/s10546-015-0120-y
关键词
Green infrastructure; Surface energy balance; Urban canopy model; Urban trees
资金
- US National Science Foundation [CBET-1058027, CBET-1435881]
- Helen Shipley Hunt Fund through Princeton University
- Swiss Federal Office for Education and Science [C00.0068]
- Div Atmospheric & Geospace Sciences
- Directorate For Geosciences [1522492] Funding Source: National Science Foundation
- Div Of Chem, Bioeng, Env, & Transp Sys
- Directorate For Engineering [1058027, 1435881] Funding Source: National Science Foundation
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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