Analysis of Thermal Environment over a Small-Scale Landscape in a Densely Built-Up Asian Megacity

Abstract

Many studies have found that larger parks might be needed to counteract the Urban Heat Island effects typical in densely populated Asian megacities. However, it is not easy to establish large parks to serve as urban cool islands in Asian megacities, where little space exists for large urban neighborhood parks. Officials in these cities would rather use small areas by replacing heat-absorbing artificial land cover with natural cover. The main objective of this study was to understand the cooling effect of changes in land cover on surface and air temperatures in urban micro-scale environments for supporting sustainable green-space planning and policy in densely built-up areas. This was achieved using measurements at different heights (ground surface, 0.1 m, and 1.5 m) for five land cover types (LCTs) and modeling with the micro-scale climate model ENVI-met. At all vertical measuring points, the average temperature over the entire measurement period had the same hot-to-cold order: asphalt > soil > grass > water > forest. However, the value dramatically decreased as the measuring points became higher. The intensity of hot and cool spots showed the highest value at surface by 18.2˝C, and declined with the height, showing 4.1˝C at 0.1 m and 3.1˝C at 1.5 m. The modeling results indicated that the well-known diurnal variation in surface insolation also occurred in our small domain, among the various LCTs. Based on these findings, providing small-scale green infrastructure in densely built-up areas could be an effective way to improve urban micro-scale thermal conditions.

Assessing the Impact of Land Cover Changes on Surface Urban Heat Islands with High-Spatial-Resolution Imagery on a Local Scale: Workflow and Case Study

“…Therefore, the highest mean LSTs and the larger fluctuations of LSTs (most in 2012 and second most in 2015) are found on built-up land. The wider gap of LSTs between different LCTs shows the potential that the local thermal environment can be improved by utilizing the heat transfer between the different LCTs [73]. It is not clearly illustrated by satellites.…”

Temporal Effects of Environmental Characteristics on Urban Air Temperature: The Influence of the Sky View Factor

“…Thus, research on the relationships between urban temperature and built environments has been conducted to help mitigate urban heat. Most previous studies have concentrated on aspects of built environments such as land cover, impervious surfaces, normalized difference vegetation index (NDVI), normalized difference built-up index (NDBI), albedo, building footprints, land uses, building roofs, and open spaces [6][7][8][9][10][11], and they have reported consistent results on those indices. Generally, increases in impervious surfaces, NDBI, and building footprints lead to higher urban temperatures, whereas increases in NDVI, albedo, and parks and open spaces mitigate the intensity of UHIs.…”

Management Strategies of Thermal Environment in Urban Area Using the Cooling Function of the Mountains: A Case Study of the Honam Jeongmaek Areas in South Korea

“…Especially, urban heat islands, which occur when the temperature in the urban area is significantly higher than the surrounding areas, is becoming more serious than and intensifies more during the night than in the daytime. It not only affects human habitability, but also may lead to the death of urban residents in serious cases [7]. In response to these urban environmental problems, sustainable and environmental cities are proposed as the basic directions for creating pleasant cities.…”

“…The Jeongmaek is the axis of the main mountain ranges of Korea and is characterized by forming near urban areas. Therefore, in densely populated Korean urban areas with difficulty in expanding large-scale greenery [7], using Jeongmaeks with good geographical and topographical conditions has the potential to improve the urban thermal environment [23]. In plans, the local cold can be effectively utilized to draw in fresh air from the Jeongmaek to the city and induce local air circulation.…”