Urban heat island induces energy consumption increment, elevated emissions of air pollutants and greenhouse gases, and compromised human health and comfort. For reducing the urban heat island intensity during summer, air temperature reduction effect of urban forests is regarded as an eco-friendly solution. However, not many studies have been done to quantify the effect of forests by species and by time. To quantify the effect of urban forests by tree species, we've measured a variety of micrometeorological variables such as air temperature, wind, radiation budget and latent heat flux, which affect evapotranspiration and nighttime drainage flow, at conifer and broadleaved forests of Gwangneung from June to August of 2016 and 2017. And temperature differences between below canopy of the forests and AWS (automated weather station) of Pocheon urban area, and between conifer and broadleaved forests, which are located at different altitudes of a mountain valley, were analyzed using the micrometeorological variables.
Results/Conclusions
The average maximum air temperature differences between above and below a canopy of forests, and between below a canopy of the forests and urban areas were -1.9℃ and -3.4℃ respectively, and they both occurred at 17:00. However, there was no difference between conifer and broadleaved forests. The air temperature differences were mainly positively correlated with accumulated evapotranspiration and solar radiation from 14:00 to 17:00, but negatively correlated with wind speed. Based on the results, we've developed a model to quantify the air temperature reduction effect during the daytime. Nighttime average air temperature difference between conifer and broadleaved forests was -1.7℃, which was due to the cold air generation from radiative cooling and the air temperature inversion that occurs when the generated cold air moves down the mountain slope. The results were evaluated in Seoul by using 28 AWSs. The evaluation showed that air temperature of each district in Seoul was negatively correlated with the area and size of the surrounding tall vegetation that drives evapotranspiration during the day, but the elevation of nearby mountains mainly affect air temperature during the night. Our research emphasizes the importance of the establishment and management of urban forests for urban air temperature reduction.