A Vegetated Urban Canopy Model for Meteorological and Environmental Modelling

Abstract

An urban canopy model is developed for use in mesoscale meteorological and environmental modelling. The urban geometry is composed of simple homogeneous buildings characterized by the canyon aspect ratio (h/w) as well as the canyon vegetation characterized by the leaf aspect ratio (σ l ) and leaf area density profile. Five energy exchanging surfaces (roof, wall, road, leaf, soil) are considered in the model, and energy conservation relations are applied to each component. In addition, the temperature and specific humidity of canopy air are predicted without the assumption of thermal equilibrium. For radiative transfer within the canyon, multiple reflections for shortwave radiation and one reflection for longwave radiation are considered, while the shadowing and absorption of radiation due to the canyon vegetation are computed by using the transmissivity and the leaf area density profile function. The model is evaluated using field measurements in Vancouver, British Columbia and Marseille, France. Results show that the model quite well simulates the observations of surface temperatures, canopy air temperature and specific humidity, momentum flux, net radiation, and energy partitioning into turbulent fluxes and storage heat flux. Sensitivity tests show that the canyon vegetation has a large influence not only on surface temperatures but also on the partitioning of sensible and latent heat fluxes. In addition, the surface energy balance can be affected by soil moisture content and leaf area index as well as the fraction of vegetation. These results suggest that a proper parameterization of the canyon vegetation is prerequisite for urban modelling.

A coupled energy transport and hydrological model for urban canopies evaluated using a wireless sensor network

“…The widely used urban canopy schemes, for example those adopted in the WRF model (including both single-layer and multilayer models), are still not very realistic in terms of their physical representation of these coupled transport processes, despite the continuous improvement in model parametrizations and the increasing model complexity in the past decade. The only exception is the vegetated UCM developed by Lee and Park (2008) and Lee (2011), including a very brief description of the hydrological modelling for tall trees and a grass surface inside urban canyon while leaving the subsurface transport of water unrepresented in the model.…”

“…Existing UCMs can be categorized broadly into two types: the single-layer (e.g. Masson, 2000;Kusaka et al, 2001;Lee and Park, 2008;Oleson et al, 2008) and the multilayer schemes (e.g. Martilli et al, 2002;Dupont et al, 2004;Kondo et al, 2005).…”

“…While the importance of linking the transport of water and energy is increasingly recognized for urban studies (Bedient and Huber, 1992;Mitchell et al, 2008), the modelling practice is still lagging behind, partially due to the complexity of the physics of water transport, particularly for unsaturated soils. Lee and Park (2008) and Lee (2011) proposed a model, in which vegetation (tall trees and grass) was incorporated into the UCM, but the hydrological model was relatively crude and their study lacked evaluation of the water transport scheme in soil.…”

Implementation of a new urban energy budget scheme in the MetUM. Part I: Description and idealized simulations

“…One way to address these constraints is to represent the city by generic building types. The most commonly used generic building type is a two-dimensional (2D) representation of a series of street canyons and roofs, first introduced by Nunez and Oke (1977) and now applied widely in the urban community (Masson, 2000;Kusaka et al, 2001;Martilli et al, 2002;Dupont and Mestayer, 2006;Harman and Belcher, 2006;Lee and Park, 2008). More information on these schemes can be found in the international urban projects of COST 715 (Fisher et al, 2006), FUMAPEX or COST 728 (Baklanov et al, 2006 and the intercomparison model exercise led by Grimmond et al (2010).…”

Simulating the surface energy balance over two contrasting urban environments using the Community Land Model Urban

“…residential lawns and parks). In this respect, the PILPSurban project (Grimmond et al, , 2011 Lee and Park, 2008) this approach can be classified as a semi-integrated vegetation approach (Vi semi ).…”