Impact of street vegetation configuration on microclimate and thermal comfort in compact low-rise local climate zone in warm-humid Colombo

Abstract

Landscape planning in urban public spaces is substantial in ensuring outdoor thermal comfort (OTC) for urbanites to improve walkability and livability. Urban microclimate in public spaces has been vastly altered due to morphology and metabolism changes as a result of intense urbanization. This challenges researchers to find ways to reduce urban heat stress by recommending mitigation measures. Nevertheless, OTC assessments in Colombo are inadequate, and the streets are the most vulnerable due to the increasing heat stress trend in Sri Lanka. Though the inclusion of greenery is the most recommended strategy, the impact of its configuration on improving OTC is lacking in research. Therefore, this study aims to investigate the impact of vegetation configuration on OTC in worst-case scenarios. The methodology comprises four phases: (i) meteorological data acquisition; (ii) case study modeling and scenario development; (iii) micro-meteorological simulations; and (iv) result comparison and recommendation. OTC is estimated employing ENVI-met simulations using physiologically equivalent temperature (PET) and predicted mean vote (PMV). The current study considers canopy density, tree height, planting location, and pattern as parameters to improve evapotranspiration and shading effects. Compact low-rise LCZ streets in Colombo resulted in 6-7 hot hours with “very hot” conditions regardless of street orientation. The impact of vegetation configuration changes on OTC is insignificant. However, the best vegetation configuration improves OTC by 42.4% compared to the no-trees scenario. This study recommends individual parallel planting in equal intervals with canopy overlaps to provide homogeneous shade coverage as the most effective. Yet, the impact is positively correlated with tree height and canopy density. Moreover, planting location is vital, and the center median is the most effective location regardless of the tree height or canopy density. The results of this study provide insights for professionals to configure street vegetation effectively to enhance OTC and for researchers to reveal further research potential in urban heat mitigation.