Verticalização e ambiente térmico urbano: estudo de cânions urbanos integrados à abordagem bioclimática em cidade de clima semiárido

Abstract

The growing population in Brazilian urban centers has triggered a gradual transformation from natural to built environments, a process particularly intensified in medium-sized cities (with populations between 100,000 and 500,000 inhabitants). These transformations contribute to the development of a typical urban climate, often characterized by increased air temperatures—known as the Urban Heat Island (UHI) phenomenon. Verticalization has emerged as an alternative to enable higher population density; however, it requires the establishment of favorable microclimatic conditions for outdoor thermal comfort at pedestrian level, especially in urban canyons. In traditional urban planning, the land lot is the main unit of land subdivision, whereas the literature emphasizes the compact city model as more sustainable and resilient. Accordingly, this study aimed to analyze the influence of verticalization on outdoor thermal comfort at pedestrian scale, considering urban form aspects (urban geometry and vegetation use) in the semi-arid climatic context of Arapiraca, Alagoas, Brazil. A predictive methodological approach was employed, based on computational simulations of 16 hypothetical urban scenarios, elaborated from a real urban area with a tendency toward verticalization. The ENVI-met software was used as the primary simulation tool. The land lot was adopted as the minimum planning unit for scenario development, considering the influence of urban geometry and vegetation on the microclimate of urban canyons. Both traditional and advanced urban planning parameters were applied, including two different types of lot merging. The climatic variables analyzed were: air temperature, relative humidity, mean radiant temperature, and wind speed and direction. In addition, the Physiological Equivalent Temperature (PET) thermal comfort index was calculated. A quantitative and qualitative comparative analysis of the climatic behavior of the variables across the different simulated scenarios (at 9 a.m., 3 p.m., and 9 p.m.) was conducted, along with correlation analysis between climatic and urban parameters. The results indicated that among the modeling parameters of the hypothetical urban scenarios, the type of lot merging and the building shape can enhance the benefits of the most influential strategy for shaping the microclimate in urban canyons: the insertion of vegetation. However, limitations were identified in the climatic mitigation provided by vegetation, mainly due to sidewalk configuration and the limited availability of permeable areas in the existing urban fabric. The composition of a Green Infrastructure was found to significantly influence the thermal mitigation of the climatic variables analyzed, while also enabling a reduction in the Sky View Factor (SVF), and maintaining a built mass that favors wind permeability across the urban grid. Additionally, SVF and the Tree Density Index (TDI) were the most influential parameters in the behavior of climatic variables. The comparison of different densification and vegetation patterns revealed the occurrence of thermal discomfort between 9 a.m. and 6 p.m., demonstrating the negative impact of verticalization at the saturation limit of lot occupation. These findings highlight the imperative for urban managers and policymakers to adopt a holistic approach to the urban planning process. In this context, predictive studies prove to be essential tools for establishing appropriate urban planning parameters to regulate urban growth and development toward sustainable and resilient cities.