Influência da arborização urbana no contexto do conforto térmico em um município do sul de Minas Gerais

Abstract

The process of urbanization has altered the natural landscape and the result has been the emergence of climatic impacts in the urban environment. One of the impacts is the rise in temperature, which is a situation faced in cities. This increase in temperature is linked to the event of heat waves, which is defined as an increase in the local climatological normal temperature for a period of more than one day. In 2021, the regions of Europe, North America, Asia and even South America were affected by this phenomenon, in which this increase in air temperature was estimated to rise by 4°C by 2100, i.e. above the 1.5°C estimated in the Paris Agreement. We can see that the populations of cities are vulnerable, thus requiring studies that explore mitigation and adaptability to urban heat. Cities are a thermal environment that exchanges heat, so urban infrastructure planning is necessary, adapting some city spaces to green infrastructures, since they are a natural ecosystem for urban cooling. Within this context, the aim of this study was to present the effect of urban afforestation on thermal comfort indicators in areas with and without tree species in a low-density urban region, given that these regions were also affected in 2023 by the phenomenon of prolonged temperature rises. To this end, on-site measurements, thermo-energy simulations and a questionnaire using subjective judgment scales were used. The on-site measurement took place on two typical summer days, where dry bulb temperature (DBT), wet bulb temperature (WBT), globe temperature (GT) and air velocity (AV) were collected from the site with trees and one without, where the difference in climatic variables was quantified and a model for 1500 typical summer days was developed using heat stack simulation. The thermo-energy simulation consisted of determining the effect of tree shading on the thermal load of the room of the building with the west façade exposed to urban trees. To do this, a hypothetical model without shading and a real model with shading were developed using the Energy Plus TM software for three typical summer days, in which the measured data was entered into the software. In order to classify thermal comfort in the living room of the building, a questionnaire was applied in accordance with ISO 9920:1995 Ergonomics of the thermal environment - Estimation of the thermal insulation and evaporative resistance of a clothing ensemble for the morning and afternoon for three typical summer days. The questionnaire data was related to the thermal resistance index (clothing) and to the measured data and the average radiant temperature. The results of the quantification of the effect of afforestation for the provided and deprived site was an average value of 3.29 °C, 3.93 °C and 9.62 °C for DBT, WBT and GT respectively for the first day and for the second day was 5.32 °C, 3.81 °C and 8.56 °C the DBT, WBT and GT respectively. The Monte Carlo simulation for 10,500 typical summer days found a difference of up to 12°C for the Gt of the built- up area. The thermo-energy simulation in the building showed that tree shading reduces the thermal load by 11.87%, 14.92% and 12.55%. In addition, there was a significant reduction in energy consumption of 14.33% for an air conditioning system with a coefficient of performance (COP) of 2.60. The thermal comfort classification in the building's living room showed that the thermal comfort temperature was 25.87 °C and the average radiant temperature that was in line with the comfortable level was 26.36 °C, and for thermal discomfort the temperature was 26.92 °C to 30.34°C and the average radiant temperature was 27.5 °C to 30.66 °C. The thermal resistance index (clothing) did not explain the answers to the questionnaire, i.e. clothing was not related to the subjective indicators of thermal comfort for the study. In summary, this study highlights the importance of trees in improving urban thermal conditions, especially in low-density cities, and provides solid evidence for the adoption of urban afforestation measures as an effective strategy to combat rising temperatures, improve the climate and thermal comfort of the population and reduce energy consumption.