Evaluation of the ENVI-Met Vegetation Model of Four Common Tree Species in a Subtropical Hot-Humid Area

TLDR

Urban trees can markedly improve the outdoor thermal environment in subtropical zones, yet the lack of fundamental evaluations of numerical simulation models hampers accurate design strategies for these climates. This study aimed to assess the physiological and thermal effects of four common tree species in Guangzhou, China, to evaluate the ENVI‑Met microclimate model. Researchers compared observed and modeled data from ENVI‑Met v4.2 Science, a three‑dimensional microclimate model, across spring and summer seasons. The ENVI‑Met model’s inability to input hourly solar radiation and its simplified tree calculations caused overestimation of leaf surface temperature, underestimation of vapor flux, and overall underestimation of trees’ thermal effects, though the model’s microclimate predictions were acceptable, indicating suitability with needed improvements.

Abstract

Urban trees can significantly improve the outdoor thermal environment, especially in subtropical zones. However, due to the lack of fundamental evaluations of numerical simulation models, design and modification strategies for optimizing the thermal environment in subtropical hot-humid climate zones cannot be proposed accurately. To resolve this issue, this study investigated the physiological parameters (leaf surface temperature and vapor flux) and thermal effects (solar radiation, air temperature, and humidity) of four common tree species (Michelia alba, Mangifera indica, Ficus microcarpa, and Bauhinia blakeana) in both spring and summer in Guangzhou, China. A comprehensive comparison of the observed and modeled data from ENVI-met (v4.2 Science, a three-dimensional microclimate model) was performed. The results show that the most fundamental weakness of ENVI-met is the limitation of input solar radiation, which cannot be input hourly in the current version and may impact the thermal environment in simulation. For the tree model, the discrepancy between modeled and observed microclimate parameters was acceptable. However, for the physiological parameters, ENVI-met tended to overestimate the leaf surface temperature and underestimate the vapor flux, especially at midday in summer. The simplified calculation of the tree model may be one of the main reasons. Furthermore, the thermal effect of trees, meaning the differences between nearby treeless sites and shaded areas, were all underestimated in ENVI-met for each microclimate variable. This study shows that the tree model is suitable in subtropical hot-humid climates, but also needs some improvement.