A Numerical Study on Mitigation Strategies of Urban Heat Islands in a Tropical Megacity: A Case Study in Kaohsiung City, Taiwan

Abstract

In recent years, with the rapid increase in global warming and urbanization, urban heat island effects (UHI) have become an important environmental issue. Taiwan is no exception, with previous studies demonstrating serious UHIs in megacities. Although existing UHI research has utilized computer simulations to analyze improvement scenarios, there are few cooling strategy studies in actual blocks of Taiwan. Therefore, this study selected a block of a megacity in a tropical region of Taiwan as a case study by ENVI-met. Five improvement strategies were tested and compared to the current situation (B0): (1) Case C1 changed to permeable pavement, (2) Case C2 increased the green coverage ratio (GCR) of the street to 60%, (3) Case C3 changed to permeable pavement and increased the GCR in the street to 60%, (4) Case C4 changed to permeable pavement, increased the GCR in the street to 60%, and increased the GCR in the parks to 80%, and (5) Case C5 changed to permeable pavement, increased GCR in the street to 60% and parks to 80%, and set the GCR on the roof of public buildings to 100%. The results showed that the average temperature of the current thermal environment is 36.0 °C, with the comfort level described as very hot. Among the five improvement schemes, C5 had the greatest effect, cooling the area by an average of 2.00 °C. Further analysis of the relationship between the different GCRs of streets (SGCR) and the cooling effects revealed that for every 10% increase in the SGCR, the temperature of the pedestrian layer was reduced by 0.15 °C.

Temperature Reduction Effects of Rooftop Garden Arrangements: A Case Study of Seoul National University

“…So far, many studies have dealt with rooftop gardens. However, the impact of rooftop gardens on the entire city or a wide area was not clearly understood, mainly by analyzing only small-scale temperature reduction effects in one space [4,[7][8][9][10][11]. The study began with the hypothesis that the effect of temperature reduction, in a wide range of areas, changes with the arrangements of rooftop gardens.…”

“…This study conducted a quantitative analysis of the temperature reduction effects of rooftop gardens on both the structures hosting them and the surrounding area. ENVI-Met, a climate simulation software [11], was adopted to derive optimal plans that maximize the temperature reduction effects achieved by each type of rooftop gardens.…”

“…In a recent study [11], a green area policy proposal was made for future improvement of Taiwan's heat environment by using the ENVI-met program. It suggests that if the green area is increased to more than 60%, the thermal environment can be improved.…”

A Study on Heat Storage and Dissipation Efficiency at Permeable Road Pavements

“…It is an urban area where temperatures are significantly higher than those in the surrounding areas [ 2 ]. Therefore, urban environmental problems will inevitably become more serious and important [ 4 ]. Previous studies about the UHI effect showed that daytime heating is the main contributing factor [ 5 , 6 ].…”

Simulation of the Urban Space Thermal Environment Based on Computational Fluid Dynamics: A Comprehensive Review

“…Huang et al (2020) simulated the wind and heat environments in Taiwan through a CFD model. They obtained quantitative indicators to improve the thermal environment and found that the green area ratio should be at least 60% to significantly improve the thermal effect [ 97 ]. Therefore, the type of urban green space, vegetation coverage, and spatial layout can all affect the urban thermal environment [ 42 , 98 ].…”