As urban impervious surface ratios, building heights, and anthropogenic heat releases are increased, urban heat island, which means urban areas are warmer than suburban areas, became serious (Santamouris et al., 2001). Especially climate change accelerates urban heat island and the urban heat is expected to increase in the future (Zhou et al. 2014). Solar radiation, which is the main heat source, will increase then net radiation in the urban canyon will also increase. Therefore, urban heat attenuation strategies should be expanded to reduce net radiation. Among the urban heat reduce strategies, urban vegetation is considered an effective method (Konarska et al., 2016). Though the shadow effect, intercept shortwave and longwave radiation, urban vegetation could reduce urban radiation. However, the numerical model for calculating attenuated radiation by urban vegetation has not been developed much yet. Most models just considered horizontal resolution. Hence, realistic influence of urban vegetation on radiation could not be verify. Therefore, the research question of this study was that how the radiation varied depending on height and leaf density of urban vegetation. In this study, we used multi-layer urban canopy model that considered vertical resolution as well as horizontal. Using that model, we simulated radiation transfer involving urban vegetation in the representative area of Seoul and varied results with different vegetation height and leaf density.
The representative area of Seoul was designed with high-rise and mid density buildings and low-density urban vegetation. In summer, when vegetation height increased 20%, the 7% of net radiation could reduce and 30% increased height made 11% net radiation reduced. And when we increased leaf density of vegetation up to 20%, the 5% of net radiation was reduced. It inferred that vertical expansion of urban vegetation was better to reduce urban heat island. From now, we should consider the vertical expansion not only horizontal expansion of urban vegetation. This study would be help for improving urban thermal environment.