Modeling a Tropical Urban Context with Green Walls and Green Roofs as an Urban Heat Island Adaptation Strategy

Urban green infrastructure (UGI) has gained increasing attention as urban heat island (UHI) mitigation and resilience strategy recently. This preliminary study investigates the outdoor temperature behavior with different fractions of selected UGIs, in tropical Colombo, the commercial capital Sri Lanka with a computer based simulation for a hot, humid end-summer sunny climate conditions in August. Seven UGI scenarios were defined under real scale modeling by ENVI-met, as T1 (existing UHI), green roofs T2,T3,T4 and green walls T5,T6,T7 by considering vegetation percentage and existing geometry. Outdoor temperatures were measured in three different locations using receptors (R1, R2 and R3) by considering the positioning with building walls and asphalt roads in the sensible height of 1.5m. Software was validated with 0.9657 R2 for simulated versus real ground measurements for T1 in same location initially. Results have enlightened that different green infrastructures significantly reduced the temperature with the vegetative fraction and highest reduction of outdoor air temperature was recorded at 1500h in a typical day. R1 and R3 had given the best reductions of temperature by 2.03°C and 1.88°C, respectively at green wall for 100% in East-West direction while R2 temperature reduction was 1.64°C for green roof 100% compared to existing UHI scenario (T1).