The urban heat island is the most important phenomenon that relates to the higher temperature compared to the surrounding rural areas. Trees and vegetation are effective at cooling surrounding air by providing shade and through evapotranspiration in the daytime and by radiative cooling at nighttime. During the summertime, in particular, the transpiration cooling effect and radiative cooling by vegetation plays an important role in mitigating thermal load in urban area and the surrounding area, and it is necessary to understand the effect of the temperature reduction depending on the kind of vegetation and biophysical mechanism. In this study, we investigate the effect of vegetation temperature reduction using a combination of net radiometer, tower profiling temperature sensor, and eddy covariance (EC) to provide information for different vegetation cooling effect at broadleaved forests (GDK) dominated by oaks (Quercus spp.) and coniferous (Abies holophylla) forests (GCK) in Gwang-neung Korean National Arboretum in 2016.
The effect of temperature reduction by evapotranspiration was 1.8℃ for GCK and 1.18℃ for GDK, and the GCK were about 35% higher. The maximum temperature reduction in GCK and GDK were 4.82℃ and 2.84℃, respectively. The average nocturnal cooling effect of GCK, 2.47℃, were higher than that of GDK, 1.83℃, and the GCK were about 25% higher. The increase in wind speed and friction velocity amplified the turbulence, which led to a decrease in the canopy temperature gradient. In addition, the cooling effect according to the height of vegetation per hour is -0.063 K h m-1 in GCK and -0.047 K h m-1 in GDK, the cooling effect of GCK is higher than GDK. This result showed that although the leaf area index of GCK was higher than that of GDK, the leaves of coniferous trees were small and sharp than those of broadleaf trees, and the land-atmosphere coupling in GCK better than GDK appeared better temperature reduction.