Modeling the environmental impacts of vegetation canopies with different lengths and leaf area densities in urban scale

Abstract

Vegetative elements can facilitate passive cooling to the environment within as well as outside the vegetation canopy itself by partitioning the absorbed radiation into sensible heat flux and latent heat flux. The objective of this paper is to investigate how to promote more efficient passive cooling by increasing the latent heat flux and reducing the heat dissipation within the vegetation canopy. A Reynoldsaveraged Navier-Stokes equation with the Boussinesq approximation and a modified k-ε turbulence model is used to model the airflow. The coupling equations of energy balance, and the heat and vapor transfer are solved to simulate the temperature and moisture fields. 12 sets of simulation are performed that consist of different leaf area densities LADs (0.2 m² m^-3, 0.4 m² m^-3 and 0.55 m² m^-3) and different canopy lengths (50 m, 150 m, 250 m and infinity). It is found that a vegetation canopy of larger LAD offers a more comfortable thermal condition at the pedestrian level. Moreover, the canopy of length 150 m shows a lower air temperature both within and downstream of the vegetation canopy. A series of sensitivity tests are undertaken to examine the role of the meteorological conditions in the overall simulation results.