O campo térmico de Alvinópolis-MG em situação sazonal de verão e inverno: uma contribuição aos estudos de clima urbano em cidades de pequeno porte

Abstract

Verifying in the city of Alvinópolis-MG the existence or not of a characteristic thermal field connected to the countryside as well as the possible air temperature differences in the intraurban scale and the associated geo-environmental and geo-urban factors, conform the regard of the research. Even though Alvinópolis-MG has not presented in the last few years indication of rapid urban growth neither horizontal nor vertical, doesn’t have grand industrial complexes and large number of vehicles (variables with potential for environment degradation), the announced investigative efforts are relevant for they aim at understanding the level of local thermal derivations produced by man in a socio-environmental particularized reality. Alvinópolis-MG is a small city in the Southeast of Brazil, on the east border of the metropolitan mesoregion of Belo Horizonte, within the Morphoclimatic Dominion of the Forested “Mar de Morros” (a large Mountain Range Spread), submitted to atmospheric systems that produce tropical and polar weather. 15.261 inhabitants live in the town being 11.433 dwellers of the urban area. In methodological terms maps of the thermal potential of the urban mesh were elaborated (Geoenvironmental and Geo-Environmental – Geo-Urban), with the application of the Multicriteria Analysis and the using of the Weighted Linear Combination (WLC). The air temperature data by intermittent moving transects were obtained at 7am, 10am, 4pm and 9pm in three days in the summer (January 2018), at 6am, 9am, 3pm and 9pm in four days of the winter (July 2018) along two routes (southeast-north and east-west) using conventional mercury thermometers of the Incoterm brand. The air temperature data in steady points were obtained within one hour breaks, in summer (March 2018) and winter (July 2018, concomitant to the moving transects registries), using nine datalogger thermometers from the Hobo brand, wrapped in Styrofoam shelters and fixed on field at 1,20 meters from the ground. The use and occupation of land in Alvinópolis-MG contributes to the intensification of the thermal differences between the countryside and the city and increases the thermal load in the space connected to the urban mesh. The thermal field is not exactly the same in all periods of the day or seasons. It is associated to the relation between the site and the apparent movement of the sun, density of the buildings, green areas, water courses, “shadow effect”, ways of collecting data. Air temperature in the urban mesh differ in relation to those of the countryside with more regularity surrounding 3pm/4pm in summer, and at 9pm in winter. At these times both registry techniques used were absolutely agreeing concerning the predomination of higher air temperature in the interior of the city in connection to the countryside. The biggest variation in air temperature occurred among points of the urban mesh, and not between the countryside and the city, in both seasons of the year and according to the two techniques used, predominantly. Heat islands were identified from weak to moderate intensity, with maximum peak in the winter, before the moving transects (3,3°C at 3pm) and the steady points (3,7° at 6am and 9pm).