Efficient Plant Types and Coverage Rates for Optimal Green Roof to Reduce Urban Heat Island Effect

Jinsil Park,Sang-Woo Lee,Kyungjin An,Yeeun Shin,Suyeon Kim

doi:10.3390/su14042146

Abstract

Green roofs are implemented to reduce the urban heat island effect; however, studies are limited to comparing the reduction in urban heat island effect before and after implementation, and the focus is on the structural stability of the building rather than urban heat island reduction. In this study, using the sky view factor (SVF) in ENVI-met, a 3D microclimate modeling program, urban spaces were classified as closed, semi-open, and open areas. Meanwhile, the green roof types were subdivided according to the vegetation coverage rates, which included grass, shrubs, and trees. The vegetation ratio was evaluated using ENVI-met to determine which of the 10 scenarios was most effective for each urban space. The thermal environment was most comfortable in semi-open areas. Therefore, the green roof scenario with 70% grass and 30% trees was effective in closed areas, 50% shrubs and 50% trees were best in semi-open areas, and 70% grass with 30% trees, or 30% grass and 70% trees, was best in open areas. This study provides a basis for creating green roof guidelines aimed at improving the urban thermal environment, as well as creating other green infrastructure elements in cities.

Highlights

Due to rapid industrial development and increasing population density, cities are facing problems such as having a high building coverage ratio and large traffic volumes.These problems increase energy consumption and artificial heat, forming a unique climate called an urban heat island (UHI) [1]
A total of six scenarios were devised based on combinations of green wall and green roof coverage ratios; the results showed that a combination of trees on curbsides, 50% green roofs, and 50% green walls, decreased the temperature by 1.90 ◦ C, suggesting that such a strategic design was needed
sky view factor (SVF) is effective for analyzing UHI phenomena and atmospheric temperperature by reflecting the shape and arrangement as well as for d ature by reflecting the shape and the arrangement of the buildings, as wellofasbuildings, for determining mining building characteristics widths

Summary

Introduction

Due to rapid industrial development and increasing population density, cities are facing problems such as having a high building coverage ratio and large traffic volumes These problems increase energy consumption and artificial heat, forming a unique climate called an urban heat island (UHI) [1]. The UHI effect is a phenomenon in which urban temperatures are higher than ambient temperatures, and photochemical reactions of pollutants form heat waves that make them vulnerable to the thermal environment [2,3,4,5]. If this phenomenon persists, it will promote thermal stress among urban residents, resulting in discomfort, as well as an increase in the mortality rates among the elderly and urban poor [6,7]. As urban areas continue to expand as the population increases, the UHI effect is accelerating; research is being conducted to quantify and improve urban thermal environments [8,9,10,11,12,13,14].

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