The effect of trees on human energy fluxes in a humid subtropical climate region
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ORIGINAL PAPER
The effect of trees on human energy fluxes in a humid subtropical climate region Zhixin Liu 1 & Robert D. Brown 2 & Senlin Zheng 1 & Lei Zhang 1 & Lihua Zhao 1 Received: 22 July 2019 / Revised: 6 April 2020 / Accepted: 3 June 2020 # ISB 2020
Abstract Trees are considered to be an effective tool for improving human thermal comfort in hot climates and have been widely used in landscape architecture. However, it is not always clear how trees affect human-environment energy fluxes. In this study, an indepth analysis of four common tree species was undertaken based on comprehensive field measurements, in terms of how each tree and its characteristics affected the energy fluxes of a person in a humid subtropical climate region. Results showed that the largest effect of trees was on radiation fluxes, with a much smaller effect on the convective and evaporative fluxes. For a person standing in shade, a tree can reduce approximately 25% of the absorbed radiation compared with an open reference point. Moreover, the cooling effect on radiation components was found to be greater in the solar radiation domain than in the terrestrial radiation domain. Solar radiation and ground surface temperature had the largest effect on a human energy budget, which was affected by characteristics of the trees and the thermophysical properties of ground surfaces. The effect from relative humidity and wind speed was quite minimal. For the four common tree species in this study, Ficus microcarpa had the best thermal performance by reducing the most absorbed solar radiation flux. This study shows a detailed empirical research about the thermal effects of trees on a person, providing recommendations for tree species selection in urban design. Keywords Microclimate . Thermal comfort . Subtropical tree species . Energy flux . COMFA
Introduction The combination of urban heat island (UHI) effect and the global warming leads to increased heat stress levels experienced by the growing urban populations (Oke 1989). The heat affects people’s health and increases mortality, especially among heat-sensitive groups like infants and elderly people (Gosling et al. 2009; Kántor et al. 2016). To alleviate extreme
Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00484-020-01948-3) contains supplementary material, which is available to authorized users. * Lihua Zhao [email protected] 1
South China University of Technology, Guangzhou, China
2
Texas A&M University, College Station, Texas, USA
thermal stress and to improve citizens’ quality of life, increasing the abundance and cover of vegetation such as trees has been considered as an effective approach, receiving increasing attention by more and more researchers (Ballinas and Barradas 2016; Bowler et al. 2010; Chatzidimitriou and Axarli 2017; Zheng et al. 2018). As a powerful tool to temper urban microclimate, trees have been shown to effectively adjust the outdoor thermal environment by providing shade, reducing wind speeds, intercepting precipit
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