Evaluation of green infrastructure effects on tropical Sri Lankan urban context as an urban heat island adaptation strategy

Abstract

Incorporation of strategic green infrastructure into urban settings has a potential to mitigate climate change, urban heat island (UHI) effect, flood risk and subsequent increase in quality of human life in general. UHI induces through low surface albedo, building geometry and absence of greenery and it deteriorates the thermal comfort and well-being of city dwellers and occupants. This study examined the implication of urban green infrastructure on enhanced microclimatic condition in tropical urban perspective while evaluating the best suitable strategy by modeling a designated site with ENVI-met microclimatic software (V4). The calibration procedure of ENVI met has been undertaken through a real ground monitoring process and the software modeling was done for selected urban setting. The model was firstly validated by reconciliation of observed in-situ measurements with simulated values. R-squared (R2) values for three different surface types such as asphalt, cement and grass were 0.91, 0.96, 0.88 for near ground (0m) and 0.78, 0.81, 0.92 for 1.5 m, respectively. The parametric studies verified that ENVI-met model can be effectively utilized to improve urban micro-scale thermal conditions in tropical Sri Lanka. The numerical simulation model of ENVI-met was used to generate micro-climatic data for the selected area of Colombo metropolitan region with six greening design scenarios such as prevailing UHI condition (T1), trees in curbsides (T2), 100% green roofing (T3), 50% green roofing (T4), 50% green walls (T5) and a combination (T6) of above mentioned green strategies (trees in curbsides+ 50% green roofs+ 50% green walls). Temperature reductions obtained from all green strategies were compared with existing UHI (T1) scenario during peak temperature in given time. The temperature reductions accomplished by T2, T3, T4, T5 and T6 green infrastructure options compared to T1 were 1.87 °C, 1.76 °C, 1.79 °C, 1.86 °C and 1.90 °C, respectively. It can be concluded that strategic design of urban greenery can effectively enhance the urban environment and outdoor thermal comfort in tropical Sri Lanka.