Recently, one of the critical environmental issues in an urban area is urban heat island (UHI). With the increase in the UHI effect, diverse negative impacts have been posed on urban areas over the world with increased cooling energy demand followed by altered thermal environment. While unusually high temperature in urban areas has been often derived from complex urban settings, the function of urban forest has been expected to be ae effective heat mitigation strategies. To examine the influence range of the cooling effect of urban forest, this study analyzed the spatial and temporal changes in surface temperature of urban forest and its surrounding areas by using Landsat imageries. Surface temperature, size of urban forest and its vegetation cover, and NDVI were investigated for 34 urban forests and their surrounding areas at a series of buffer areas in Seoul, South Korea.
Results/Conclusions
The mean temperature of urban forests was lower than that of the overall city, and the threshold distance from urban forests for cooling effect was estimated to be roughly up to 300 m. The group of large-sized urban forests showed significantly lower mean temperature than that of small-sized urban forests. The group of urban forests with higher NDVI showed lower mean temperature than that of urban forests with lower mean NDVI in consistent manner. Negative linear relationship was found between the temperature and size of urban forest (r = -0.36 to -0.58), size of vegetation cover (r = -0.39 to -0.61), and NDVI (r = -0.42 to -0.93). Temporal changes in NDVI were examined on a specific site, Seoul Forest separately that has experienced urban forest dynamics. Surface temperature of the site decreased as NDVI improved by land use change from a barren racetrack to a city park. It was considered that NDVI could be a more reliable indicator for evaluating the cooling effect of urban forest than the size of urban forest and vegetation cover themselves. The findings from this study can be useful to develop planning and management of urban forest.