Wind and greenery effects in attenuating heat stress: A case study

Abstract

This paper aims to assess the effects of urbanization on heat stress comparing two neighbourhoods in the tropical city of Rio de Janeiro, Brazil, that differ in terms of building density and vegetation cover. The outdoor heat stress was evaluated by the Wet Bulb-Globe Temperature (WBGT) Index, which considers the combined effect of air temperature, relative humidity, solar radiation and wind speed, during the year of 2016. The urban neighbourhood presented statistically (p < 0.01) higher WBGT levels (mean value 23.48 °C), than the suburban neighbourhood (mean value 22.0 °C). The results highlighted the effect of low wind velocities on heat stress in the urban environment over 75% of the time. Building spacing and street orientation considering the most frequent wind directions must be taken into account during the urban planning process. Otherwise stagnant air conditions in urban environments become a common feature that cannot be reverted. Under such circumstances, green areas such as pocket parks, green roofs and green walls should be implemented to mitigate heat stress. Public policies for many neighbourhoods in Brazilian cities are necessary to increase vegetated areas aiming to improve conditions of well-being. • Vegetation played a significant role in controlling urban heat fluxes. • Considerable differences in heat stress conditions were observed between the two areas. • Urban planning guidelines should recommend green spaces and street orientation to optimise wind flow.