The Design of Facade-Integrated Vertical Greenery to Mitigate the Impacts of Extreme Weather: A Case Study from Hong Kong

Vertical greenery not only helps to cool the surfaces of buildings but, more importantly, it can also mitigate the Urban Heat Island effect. The growth of vertical greenery is highly dependent on ongoing maintenance, such as irrigation. Wind-driven rain serves as a natural source of irrigation for vertical greenery. Wind-driven rain simulation was conducted on a typical high-density and high-rise case in Hong Kong to first classify the wind-driven rain harvesting potential on the facade with very high, high, moderate, low, and very low levels. Then, Scenario 1 (very high potential), Scenario 2 (very high + high potential), and Scenario 3 (very high + high + moderate potential) regarding vertical greenery in locations with three levels of wind-driven rain harvesting potential were simulated in ENVI-met to assess its Urban Heat Island mitigation effect. The maximum temperature reduction on the street occurs between 12 p.m. and 3 p.m., indicating the greatest mitigation of the Urban Heat Island effect. Scenario 1, Scenario 2, and Scenario 3 achieve a maximum temperature reduction of 0.76 degrees C, 0.88 degrees C, and 1.06 degrees C, respectively, during this time period.