## 4 Discussion  
The main findings from this study are as follows. It was found that rooftop greening is possible for 311,793 buildings (42% of all buildings). The total suitable area for rooftop greening is 33,288,745 m\({}^{2}\), which is 50% of the total rooftop area of Seoul. The total park area of Seoul is about 168,890,000 m\({}^{2}\). Thus, about 20% of total green areas could be increased, once suitable rooftop areas are completely changed to green roofs. In addition, 145,366 additional plantings are possible in the study area. Such results show that even if many roadside trees (about 403,161) are already planted in the study area, additional roadside trees can be planted in many other spaces. This study analyzed the effects of temperature reduction resulting from rooftop greening and roadside tree planting through Envi-met simulations. It was shown that the introduction of green roofs reduced temperatures by 0.13 \({}^{\circ}\)C to 0.14 \({}^{\circ}\)C and roadside trees reduced temperatures by 0.14 \({}^{\circ}\)C to 0.6 \({}^{\circ}\)C. Both greening and tree planting showed maximum temperature reduction after sunset, when latent heat effects begin to increase. The maximum temperature reduction effect did not differ much from prior research, but the temperature reduction effect was measured at a somewhat lower value. This is because unlike prior studies [38; 39], this study applied only the actual applicable rooftop green locations. The effect of roadside trees has also been reported to reduce temperatures by up to 1.2-3.3 \({}^{\circ}\)C [18], but in this study, it was found that the effects were not as strong because roadside tree planting was mainly possible around the sites. This means that the physical form of urban spaces not only determines the planting areas and locations, but also the effects. Meanwhile, the results of this study are expected to be useful for establishing greenery planning of local governments. Rooftop greening and roadside tree planting are classified as public goods that are publicly supplied. The local government should first identify what areas and how much room is available for the effective supply and management of rooftop greening and roadside trees. However, green roofs and roadside trees are very small \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{3}{c}{**Air Temperature (\({}^{\circ}\)C)**} \\ \cline{3-5}
**Simulation** & & **A** & **B** & **C** \\ \hline \multirow{2}{*}{existing condition} & mean (day) & 26.67 & 27.17 & 28.33 \\  & max (hr) & 31.93 (18:00) & 33.08 (18:00) & 34.12 (16:00) \\ \hline \multirow{2}{*}{rooftop greening} & mean (day) & 26.64 & 27.11 & - \\  & max (hr) & 31.82 (18:00) & 32.96 (18:00) & - \\  & reduction effect (hr) & \(\mathbf{\
abla}\)0.12 (21:00) & \(\mathbf{\
abla}\)0.14 (21:00) & - \\ \hline \multirow{2}{*}{roadside tree planting} & mean (day) & 26.43 & 27.11 & 28.11 \\  & max (hr) & 31.36 (18:00) & 32.95 (18:00) & 33.74 (16:00) \\ \cline{1-1}  & reduction effect (hr) & \(\mathbf{\
abla}\)0.59 (20:00) & \(\mathbf{\
abla}\)0.14 (19:00) & \(\mathbf{\
abla}\)0.47 (18:00) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Temperature reduction effect of rooftop greening and roadside tree planting. compared with other urban facilities, and suitable spaces are widely distributed throughout cities. In addition, there is no specific analysis of where the facilities could be introduced due to the lack of analysis data and the vastness of the data. This study specifically analyzed suitable locations, areas, and quantities of rooftop greening and roadside tree planting in a metropolitan city. In addition, the entire processes were developed by using an automated data analysis model, and thus the speed and convenience of planning the introduction and expansion of green areas was increased.