Cooling effect of roof greening with water misting in a cold region during the summer

In this study, the cooling effects of urban green roofs and water misting were explored for buildings in cold regions during the summer. We selected five different plant types and water-misted areas on the roof of a commercial building in Xi’an, and obtained temperature and humidity field measurements for the planted and water-misted areas, and concrete roofing as a control. Measurements and theoretical analysis confirmed that the direct cooling effect (effect on roof surface temperature) of the water-misted area was about 12 °C. The effect of privet was highest among the plants at about 22 °C and the other plants also had remarkable cooling effects. Moreover, the plants had significant effects on stabilizing temperature fluctuations. In terms of the indirect cooling effect (effect on air temperature and indirect effect on roof surface temperature), that of the water-misted area reached 4.14 °C and privet was highest with about 4.68 °C at a height of 300 mm. The mechanisms responsible for the indirect and direct cooling effects of plants and water misting were also analyzed. The results confirmed that different types of roof plants and water-misted areas at various heights could increase the environmental relative humidity to indirectly affect the air temperature. Finally, the direct and indirect cooling effects of roof plants and water-misted roofs in cold regions were compared with green roofs in other climate zones, as well as the other functions of water-misted roofs, such as landscape beautification, rainwater collection, and reuse.