Modeling microclimatic effects of trees and green roofs/façades in ENVI-met: Sensitivity tests and proposed model library

Abstract

Urban green infrastructure furnishes one of the most effective ways to mitigate and adapt to climate change and the consequent thermal environment deterioration. ENVI-met, a holistic computational fluid dynamics model with various plant modules, has become a principal simulation tool to evaluate the thermal effects of urban greenery. This study emphasized the significance of clear and accurate ENVI-met vegetation modeling, aiming to formulate strategies to boost modeling data quality, veracity and rigor of ENVI-met-based simulation studies. This study applied a two-step framework. First, a series of sensitivity tests were conducted under hot and humid meteorological conditions to identify the microclimate-sensitive parameters and their relative cooling effects at the pedestrian level. The results identified leaf area density as the most significant parameter in ENVI-met tree modeling. Some compromises on root properties' input accuracy could be tolerated since they would not considerably hamper the overall simulation quality at the pedestrian level. For green roof/façade modeling, leaf area index and leaf angle distribution were significant and should be accurately input to ensure simulation quality. Second, for the microclimate-sensitive parameters in modeling, this study used commonly-planted species in subtropical South China cities to demonstrate a systematic workflow of developing an ENVI-met vegetation model library. The library could include basic plant physical traits, plant albums, reference values of the microclimate-sensitive parameters, and recommended alternative modeling data sources. The vegetation model library could provide a helpful and actionable package from which researchers can quickly obtain accurate input values without highly specialized knowledge or instruments.