Relationship between urban thermal environment and urban forest in Seoul, South Korea

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Peter Sang-Hoon Lee, Jiyeon Oh and Dasol Son, Department of Urban & Regional Development, Hanyang University, Seoul, Korea, Republic of (South)

Background/Question/Methods
One of the functions of urban forest to urban area is mitigating urban heat island effect. That effect on a micro climate level has posed negative impacts on a city with increased cooling energy consumption followed by changeable ambient temperature. While unusually high temperature in urban areas has been often originated from a complex urban environment, the function of urban forest has been considered as a useful mitigation strategy to the issue. To examine the cooling effect of urban forest and their influence range, this study analyzed the spatiotemporal changes in land surface temperature (LST) of urban forest and surrounding areas by using Landsat imageries. A suite of variables such as LST, physical characteristics of urban forests (size in area and altitude), and Normalized Difference Vegetation Index (NDVI) were investigated for 34 urban forests in Seoul, South Korea and their surroundings using a series of outside buffers.
Results/Conclusions
The mean LST of urban forest was lower than the overall city of Seoul. The group of large urban forests showed lower mean LST than that of smaller urban forests. The outcome from the group of high urban forests was similar to those of large urban forests. The group of urban forests with higher NDVI showed lower mean LST than that of urban forests with lower NDVI in a consistent manner. Negative linear correlations were found between the LST and size of urban forest (r = −0.36 to −0.58), size of vegetation cover (r = −0.39 to −0.61), altitude of urban forest (r = −0.31 to −0.46), and NDVI (r = −0.42 to −0.93) in the year of 2002, 2004, 2009, 2015 and 2019, respectively. Monthly and seasonal changes in NDVI were examined separately on the specific site of Seoul Forest, that has experienced urban forest dynamics. LST of the site decreased as NDVI improved by a land-use change from a racetrack with the limitation of vegetation to a city park with a variety of vegetation. In conclusion, the average threshold distance by cooling effect of urban forests was estimated to be roughly up to 300 meters. It was considered that NDVI or the feature of vegetation could be a reliable factor for estimating the cooling effect of urban forest compared to the size of the urban forest and/or vegetation cover.