Desenho urbano climaticamente orientado: a influência da vegetação no ambiente térmico externo

Abstract

Vegetation can produce measurable positive effects on the thermal field of urban spaces. In view of thermal inadequacies in outdoor spaces, there is a need for projects and urban plans which consider the use of vegetation as strategic element for the creation of thermal comfort conditions in open spaces. In this sense, the relevance of this study is the proposition of an index which estimates the amount of vegetation fraction needed to reduce the air temperature in urban environments. The index was developed for the city of Curitiba, specifically for its central arteries such as Avenida Sete de Setembro and Avenida Linha Verde. Additionally, pilot studies for the cities of Geneva, Paris and São Paulo are presented. The experimental research uses field measurements for collecting microclimatic data and computer simulations with the ENVI-met model, which allowed the comparison of current and alternative scenarios. All simulations were carried out for summer conditions. The thermal comfort indices Physiological Equivalent Temperature (PET) and Universal Thermal Climate Index (UTCI) were used to assess levels of thermal stress at the pedestrian level. In general, it was observed that the insertion of green areas (particularly under dense canopy) could reduce the daytime heating in urban areas, with substantial changes in heat stress categories. The maximum reduction of air temperature was 2.5°C, observed in the pilot studies in São Paulo and Paris. In the Sete de Setembro the maximum reduction of air temperature was 1.2°C and in the Linha Verde it was 1.5°C. It was found that contributing factors to ambient temperature reductions are the distribution of trees and the canopy density (related to the shadow quality). The proposed index (ratio between the increase of vegetated over built-up area) may explain the reduction of mean air temperature by 83.1%. From its application, it can be concluded that a 1°C reduction in air temperature should be expected for an increase of 49% in vegetated fraction. In cities impacted by heat waves, the advantage of greenery insertion is the relatively low investment with considerable benefits in changes of heat stress categories. In cities impacted by heat waves, the advantage of greenery insertion is the relatively low investment with considerable benefits in changes of heat stress categories. The importance of the index (and the proposed methodology behind it) lies in the possibility of its application in climate- responsive urban design.