Abstract
Large cities with a high concentration of high-rise buildings are shaded by urban canyon. This brings a cooling effect compared to the space exposed to the sun, but is not always cool due to the longwave radiation emitted from buildings and the built environment. We tested the micro-scale effects of major external spatial factors, trees, and buildings, under shade on longwave radiation shifts to understand the effects of large shaded areas in megacities. Incoming and outgoing longwave radiations (ILR and OLR, respectively) were found to decrease the overall observation by time zone. Longwave radiation on a micro-scale was also inversely proportional to the tree volume. From mean radiant temperature (MRT) analysis, we found that about a 10% decrease in MRT could be achieved by increasing tree volume by around 50%. Larger tree volumes corresponded to greater blocking effects on longwave radiation. Considering the tree volume, a multilayer urban tree canopy composition can more favorably improve the thermal environment and energy sustainability of a city compared to a single-layer canopy. Larger trees planted with harmonious shrubs are the most effective in reducing longwave radiation.
Highlights
As high-density areas increase with urbanization, urban canyons are formed with high-rise buildings casting shade [1]
We focused on determining the effect of tree and building deployment on the mean radiant temperature (MRT), based on shifts in longwave radiation time in urban apartment areas
This study examined the reductions of net longwave radiation and MRT near residential building complexes using trees and building compositions according to the layouts of old and new apartment complexes considering longwave radiation in the megacity of Seoul
Summary
As high-density areas increase with urbanization, urban canyons are formed with high-rise buildings casting shade [1]. High-rise high-density residential complexes are continuously constructed in metropolitan cities where land is scarce [3]. This intensifies the UHIE, even though children and elderly people who are vulnerable to heat remain active in the daytime [4]. Dense residential complexes cause significant shadows in metropolitan areas. These many shaded areas decrease the solar radiation reaching the surface or space. This mitigates the UHIE [5,6]. Shadows that block heat are important in high-population-density urban residential areas with high-rise buildings
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
