Evaluating the cooling effects of greening for improving the outdoor thermal environment at an institutional campus in the summer

• Quantifying the cooling effects of trees and grass roofs.
• The ENVI-met simulation tool is verified with on-site measurements in this study.
• The average temperature could be reduced by up to 2.27 °C by increasing the existing quantity of trees by 20%.
• The addition of trees and grass roofs together could reduce temperatures by up to 2.29 °C.

The thermal environment can have several effects on people who use outdoor spaces; especially on university campuses were the thermal environments of educational living spaces are important. This study focuses on the importance of greening as a potential method for passive cooling and for use in reducing ambient air temperatures, especially at a pedestrian level. There are two main strategies of greening modification. These two strategies have been proposed to improve campus environments and aim to include more greening area by adding trees to current green areas and by growing a grass layer on the rooftop of educational buildings. In this study, two approaches are presented, including an on-site measurement and a numerical simulation model that uses ENVI-met. These greening modification methods were investigated regarding their local cooling effect. This study was conducted at the institutional campus of Saga University, Japan. We hypothesized that the average maximum temperature would decrease and reach 2.27 °C in the peak of the summer (at 15:00) when the quantity of trees was increased by 20%. Furthermore, combining both modification methods led to the largest air temperature decrease with an average and maximum of 0.24 °C and 2.29 °C, respectively. The results of this study allow university decision makers and planners to identify more precise green campus policies, which are necessary for improving the educational environment.