Air Temperature and Urban Form Studies in Open Spaces. The Case of Campinas, Brazil

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1 Air Temperature and Urban Form Studies in Open Spaces. The Case of Campinas, Brazil Claudia Cotrim PEZZUTO, Lucila Chebel LABAKI, Lauro L. FRANCISCO FILHO School of Civil Engineering UNICAMP university of Campinas, PO Box 6021, Campinas, Brazil Tel.: , Fax: ABSTRACT: The aim of this work is to evaluate the influence of urban form in climatic conditions of open urban spaces in the city of Campinas, Brazil. The method consists in collecting data to obtain the horizontal distribution of the meteorological variables (temperature) in an open urban area in the city. The city is located at the southeast region of Brazil, in the geographical latitude 22 53'S; it occupies a total area of 800 Km 2 at an average altitude of 680 m, with a population of near one million inhabitants. The object of study is a central area of the city, characterized by different configurations and land use. The study area was defined through visits and compilation of maps and cartographic bases. Thematic maps are elaborated with the purpose of detecting the variables that influence in the modification of the urban climate. Fixed points were analysed with continuous data registration. The expected result of this research is the possibility of contributing with urban planners, to improve thermal comfort and quality of life in urban environments. Conference Topic: 3 Comfort and well being in urban spaces Keywords: urban climate; thermal comfort; heat island 1. INTRODUCTION The quality of urban spaces has been subject of several studies in the last years in many countries. These studies are accomplished with the aim of contributing to the life quality of the population. In this context, the effect of the climate in the urban spaces is particularly important for people who develop their activities in those areas, thus indicating the need to improve the conditions for human comfort in such spaces. Urban climate and thermal comfort in outdoor spaces are affected by many factors, like the size of the city, land use, the density of the built area, building design and disposition in urban areas, height of the buildings, orientation and width of the streets, heat-absorbing construction materials, pavement surfaces and the presence of vegetation, the effects of parks and other green areas and the design of details of the buildings which affect the external conditions [1]. Several parameters of the urban geometry affect the temperature differences in the urban area, and there are studies, which demonstrate a good correlation among them [2, 3, 4]. In studies about urban climatic variations different methodologies have been adopted, like data collected from meteorological stations, mobile measurements in transects, remote sensing and mathematical models. Several authors use the method of mobile measurements in transects in order to obtain the horizontal distribution of air temperature in urban areas. [5, 6, 7]. The use of satellite images obtained by remote sensing has also been frequently adopted [3, 8, 9]. Image interpretation allows the establishment of dynamic relationships about land use and the thermal field, thus contributing as an important tool for urban planners. The aim of this work is to contribute for climatic analysis of urban open spaces, with regard to thermal comfort and quality of life. The chosen case study is a central area of the city of Campinas, in the State of São Paulo, Brazil, since it is characterized by a great building concentration, population density and complexity of land use. 2. METHODS 2.1 Study area The city of Campinas is situated in the Southwest region of the State of São Paulo, at a distance of near 100 km from São Paulo, in the geographical coordinates Latitude 22 53'20"S, Longitude 47 04'40"W, occupying a total area of 796,40 km 2 (urban perimeter 388,90 km 2 and rural perimeter 407,50 km 2 ) with an average altitude of 680 m. Its population, according to the Brazilian census of 2000, is inhabitants [10]. The city climate presents the following characteristics: the highest average maximum temperature occurs in February (29,9 C) and the

2 lowest average minimum temperature in July, (12,2 C). Relative air humidity varies from 64,3% (August) to 77,7% (January and February). The largest temperature amplitude occurs in winter, the driest period, up to 12,9 C in August, and an average for those months of 12,3 C. In summer, more humid season, the average amplitude is around 10,4 C [11]. The study area is located in a central region of the city. Points for the installation of the equipments were chosen through visits and observations, analysis of maps and aerial photographs, identifications of land use. The points were located in different use configurations and urban occupation with the objective of evaluating the occurrence of heat islands in different areas of the city. 2.2 Measurements Temperature measurements were carried out at nine fixed points, distributed along the chosen area. Data were collected in continuous registrations, through loggers installed at places in the shadow, avoiding direct solar radiation, at a height from 1,50m to 2,00 m. Three of the loggers were Sato model SK- L200 TH, and the other six Testo model and Measurements occurred in March of 2004, in days of clear, cloudy or partially cloudy sky. In rainy days data were discarded. So, the reported analysis covers the days 12, 13 18, 19, 22, 23 and 24/03/2004 (autumn equinox), days with stable weather. Data collected at these nine points were compared with those from the Meteorological Station of the Centre for Agricultural Research (CEPAGRI) in the Campus of the University, which is located outside the urban centre of the city. Figure 1 shows the distribution of the points in the urban area of Campinas. 3. RESULTS Colleted data in different measurement points in the urban environment allowed the identification of the thermal differences in the study area. For the analysis average, maximum and minimum air temperatures were considered, corresponding to the seven daily values (12, 13, 18, 19, 22, 23 and 24/03/2004). These data are shown in table 1, as well as average temperature amplitudes. It can be seen that average maximum temperature was measured in point number 4, which is located in an area of high building and population density. The largest temperature amplitude was registered in the meteorological station, which can be explained by the faster night cooling of the area where the station is situated. This area has a much lower degree of urbanization. Figure 2 compares graphs of results from the measurement points and the meteorological station. It can be seen that temperatures at all points in the urban area are higher than in the station in the period of nocturnal cooling and all night long. In periods of sunshine, temperatures in the fixed points are either above or lower than those from the station. It can be observed that the largest differences between the meteorological station and the urban area refer to minimum temperatures. Figure 1: Aerial photograph of the region, with the measurements points

3 Table 1: Values of average minimum and maximum temperatures and thermal amplitude Point Average Minimum Temperature Average Maximum Temperaature Thermal amplitude 1 19,81 27,91 8, ,99 27,56 7, ,76 27,57 7, ,76 29,98 7, ,39 27,04 7, ,67 29,79 10, ,51 25,87 5, ,62 29,30 9, ,09 25,97 3,88 Meteorologi cal Station 16,62 27,27 10,65 Through these data it can be inferred that temperature is related to the urbanization process. Since the study area has a meaningful urban concentration, evaporation is reduced and roughness is increased. This process is also due to the thermal properties of the buildings and construction materials, which contribute to the thermal storage during the day and hinder faster night cooling. On the contrary, the area where the station is located, with a fast night cooling is related to a less dense urban occupation. The intensity of heat island was also analysed, through the relative thermal differences among the several measurement points. The methodology adopted by Gómez et al. [12]. apud Brandão [13], was used for the analyses. Temperature (ºC) 31,0 29,0 27,0 25,0 23,0 21,0 19,0 17,0 15,0 0h 6 h 12 h 18 h 23 h Time Measurement (h) Urban Point Urban Point Meteorological Station Figure 2: Average hourly temperature, at the urban points and Meteorological Station This method establishes the following categories: heat island of weak intensity, when the thermal differences oscillate between 0 and 2 C, moderate heat island, with differences between 2 and 4 C, strong intensity, when differences oscillate between 4 and 6 C, very strong intensity, when the differences higher than 6 C. Starting from the point with the smallest temperature, it is possible to obtain the thermal difference for each analysed point. Figure 3 shows the thermal differences obtained for the measurement points. It can be observed that in the period of night cooling, (21:00) and in the middle of the dawn period (3:00) the hottest areas of the city were points 4 (9 pm with 2,09 C and 3 pm with 2,3 C) and point 9 (9 pm with 2,11 C and 3 pm with 2,90 C), resulting in a heat island of strong intensity. Air Temp. Differences (ºC) 3,50 3,00 2,50 2,00 1,50 1,00 0,50 0, Location of Observation Points 3 h 9 h 15 h 21 h Figure 3: Temperature differences in the measurement points '

4 Data supplied by IBGE - Brazilian Institute of Geography and Statistics [13], about the Census of 2000 allowed elaborating the maps of population density and habitation units density for the study area (figures 4 and 5). It can be seen from the aerial photograph (figure 1) that points 4 and 9 are located in areas densely occupied by buildings, with little vegetation, intense movement of pedestrians and vehicles, high population density. All these factors contribute to the intensification of the heat island in the night period. It is also noticed that point 4 presents an intense magnitude of heat island at 3 pm (3,08 C). However at this hour point 6 presents the largest intensity. This point was located in an ambient with metallic roofs, tall ceiling height and good ventilation. So it is necessary a new collection of data to verify the real occurrence of heat island in this point. The morning period did not present meaningful temperature differences, with the exception of point 6, which has the influence of external factors, as commented before. Points 5 and 3 present the lowest values. The first one is located in an area of medium construction and low population density; point 3 is located in a depression area with a low population and habitation units density. Figures 4 and 5 also show that the great intensity of heat island in the urban centre really occurs in highly urbanized areas. Analysing the points with the smallest occurrence of heat island (points 5 and 3) it can be noticed that they are located in areas with low population density and medium habitation units density for inhabitant. Figure 4: Population density map for the study area Figure 5: Habitation units density for the study area

5 4. DISCUSSION When analysing the phenomenon of heat island it can be verified its strong relation with urbanization. The areas with high building and population density present strong heat island intensity. On the other hand, points of coolness in areas of low demographic and building density are observed. It was also verified that the temperatures of the urban area were almost always above those at the meteorological station, proving the influence of the urbanization in the local climate. It is shown that the climatic changes induced by the urbanization are meaningful. In other words, the climate in the cities suffers influence of the complex group of the urban structure: geometric characteristics of the buildings, properties of building materials, density of the built area, land use, buildings height, orientation and width of the streets, subdivision of the lots, the effects of the parks and other green areas. However, thermal comfort in open spaces and quality of life in the cities can be reached if urban planners take into account physical parameters together with environmental data for urban areas. REFERENCES [1] Givoni, B. Climate considerations in building and urban design. New York: Van Nostrand Reinhold., [2] Eliasson, I. Urban nocturnal temperatures, street geometry and land use, Atmospheric Environment. v. 30. n.3, p , [3] TSO, C. P. A survey of urban heat island studies in two tropical cities, Atmospheric Environment. v. 30. n.3, p , [4] Lombardo, M. A. Ilha de calor nas metrópolis. O exemplo de São Paulo. São Paulo: Hucitec [5] Yamashita, S. Detailed structure of heat island phenomena from moving observations from electric tram-cars in metropolitan Tokyo. Atmospheric Environment. v. 30. n.3, p , 1996 [6] Fontes, M. S. G. C., Efeito climático das áreas de fundo de vale no ambiente urbano: o caso de São Carlos SP.. PhD Thesis, Escola de Engenharia de São Carlos, USP (1998} [7] Lindberg, F.; Eliasson, I.; Holmer, B. Urban geometry and temperature variations, In FIFTH INTERNATIONAL CONFERENCE ON URBAN CLIMATE, ICUC, Proceedings, Lodz, Poland, [8] Souza, L. C. L Identificação de ilhas urbana de calor através da interpretação de imagem de satélite. In: II ENCONTRO NACIONAL DE CONFORTO NO AMBIENTE CONSTRUÍDO, Anais...Florianóplois, SC, pp , [9] Dousset, B.; GOURMELON, F, Surface temperatures of the Paris basin during summertime,using satellite remote sensing data. In FIFTH INTERNATIONAL CONFERENCE ON URBAN CLIMATE, Proceedings...Poland, [10] Secretaria De Planejamento, Desenvolvimento Urbano E Meio Ambiente Prefeitura Municipal de Campinas,2003, ndex.htm [11] CHVATAL, K. M. S.; Labaki, L. C.; Kowaltowski, D. C. C. K. Caracterização de climas compostos e proposição de diretrizes para o projeto bioclimático: o caso de Campinas. In: V ENCONTRO NACIONAL DE CONFORTO NO AMBIENTE CONSTRUÍDO, Anais...Fortaleza - CE, [12] Gomez, A. L. et al. El clima de la ciudades españolas. Madrid, Editora Cátedra, 1993, 267 p. [13] Brandão, A. M. P. M. O clima urbano da cidade do Rio de Janeiro, In Monteiro, C. A. F. E Mendonça, F. Clima urbano, p, [14]