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URBANISM

Heat in the cities

Research studies look for ways to protect residents of big cities from the effects of high temperatures

The Presidente João Goulart high-rise in downtown São Paulo: the benefit provided by trees is of limited scope

Eduardo CesarThe Presidente João Goulart high-rise in downtown São Paulo: the benefit provided by trees is of limited scopeEduardo Cesar

On successive days of record-high temperatures experienced in recent years, residents of big cities are among the first to feel the effects of climate change, aggravated by “heat islands,” a phenomenon that occurs primarily in metropolises. The concentration of asphalt and concrete, along with an insufficiency of green space and excessive air pollution, favor the rise in temperature. Consequently, urban planning efforts now face the challenge of promoting a comfortable environment. In public spaces, trees are the most valuable allies. Sitting under a large tree with a dense canopy, people will feel much cooler than they would a few meters away, even if the air temperature measures only 1 or 2 degrees Celsius (oC) lower. Depending on soil-surface-atmosphere interactions, a person may feel 10 to 13oC. cooler under the tree. On hot days, the difference can be as much as 20oC. The Environmental Comfort and Energy Efficiency Laboratory (LABAUT) of the Technology Department of the School of Architecture and Urbanism, University of São Paulo (FAU-USP) is conducting projects that attempt to understand the complicated climactic relationships that prevail in cities and find ways to make life more comfortable from an environmental standpoint.

“Trees are the kind of amenity that makes an enormous difference in terms of temperature, humidity, wind, and sunlight,” says Denise Duarte, an engineer and coordinator of LABAUT and a professor at the FAU. However, the effect of a single park, plaza or even a tree-lined avenue is only local. Anyone who lives in the buildings in the immediate vicinity will experience a certain amount of relief from the heat, but a few floors higher or on the next block conditions will not be the same. Duarte recommends that urban planning and design consider providing a “network of green infrastructures” with tree-lined streets that connect the vegetation at ground level to other public spaces in the city.

Architect Leonardo Marques Monteiro, deputy coordinator of LABAUT, has developed a thermal comfort index – the Perceived Equivalent Temperature (TEP)—tailored to the specific conditions in Brazil. Internationally, more than 100 calculation models are used to arrive at an index that serves as a parameter to evaluate thermal comfort. The most widely used, the Physiological Equivalent Temperature (PET), compares the difference between what people feel in an open space with what they experience in a closed environment. That model takes into account the physiological characteristics of a body that represents the average person in Germany, where the index was developed.

“My concern was not so much with the physiology of the body, but with the way in which people respond,” Monteiro explains. His method involves a large number of interviews with passers-by at different locations in order to understand the types of activities people engage in at each site and how the different social groups feel in those spaces. The questionnaires include questions about thermal sensation and satisfaction. The results are available to assist research studies and public or private projects.

Monteiro argues that the planning of an urban area must take into account the diversity of those experiences. “The way a city is used is very heterogeneous. There are all kinds of people in all kinds of situations,” he says. “What is important is to create a variety of types of spaces so that people can choose what they prefer.”

A green corridor in Vila Madalena: connections among forested areas improve environmental comfort.

Eduardo CesarA green corridor in Vila Madalena: connections among forested areas improve environmental comfort.Eduardo Cesar

The Elderly
Researchers coordinated by Fábio Gonçalves, a professor at the USP Institute of Astronomy, Geophysics and Atmospheric Sciences (IAG-USP), conducted studies under a thematic project entitled Human biometeorology: analysis of the effects of the environmental variables (meteorological, thermal comfort and air pollution) and climate change on the geriatric population of São Paulo city, which ended in June 2016. They focused on a population group that is particularly vulnerable to excessive heat: the elderly. According to Monteiro, who took part in the project, older folks do not perceive a hot environment the same way as young people do, especially under conditions of high humidity, when perspiration is less effective at dissipating the heat. The elderly may feel comfortable, but in reality, they are experiencing thermal stress because of the heat. “By improving the vegetation at ground level, however, we can achieve comfort most of the time,” Monteiro says.

The term “environmental comfort” designates a state in which someone is able to satisfactorily adapt to thermal, light, sound, and ergonomic conditions. In designing buildings, environmental comfort is considered when energy efficiency and exposure to sun and wind are issues. In open areas, the problem is more complicated. It demands a convergence among different fields of knowledge, such as meteorology—biometeorology in particular—geography, architecture, and engineering. According to Duarte, who participated in the thematic project, architecture plays a unifying role in that context. “Architects take a more humanistic view, they look beyond numeric models,” she says.

Research in outdoor areas demands an arduous measurement process that involves different types of equipment, and plenty of it. Researchers are unanimous in lamenting that Brazilian cities do not have more meteorological stations. The project entitled Participative model for evaluation of comfort conditions in open urban spaces, now in progress and headed by architect Alessandra Prata, a professor at FAU-USP, resulted in the development of an application for cellphones, now being tested, that volunteers could use to report their degree of environmental comfort at different sites in the city. The primary objective is to relate thermal sensation to data from meteorological stations that are to be installed in different urban spaces, and make that data available for use as a foundation for public policies.

A succession of spaces
Duarte points out that cases of Brazilian cities that have proper planning for environmental comfort are rare. In metropolises, one finds some sites that, she says, function as oases. She refers to forested urban parks, such as Trianon Park in São Paulo, which provides relief on days of intense heat on Avenida Paulista. “But those points are few and far between. There are huge areas of the city that have no vegetation at all.”

The perspective of continuity is important. “What we lack is the kind of planning that creates a succession of forested spaces, like urban oases, so that travel around the city is more comfortable,” the researcher says. Ground-level vegetation, with its good natural ventilation, coupled with a satisfactory balance between shady and sunny spaces, is the key factor in providing relief from the heat. These features can be supplemented with pergolas (structures that supply shade and support climbing or trailing plants) and by the presence of streams or reflecting pools.

Concentration of buildings in the central part of São Paulo, and Parque da Aclimação, in the southern zone: inequality in ground cover

Eduardo CesarConcentration of buildings in the central part of São Paulo, and Parque da Aclimação, in the southern zone: inequality in ground coverEduardo Cesar

Thought must be given to the proper kind of tree for each type of climate. In 2012, during the United Nations Rio+20 conference on climate, a park was inaugurated in the district of Madureira, in the northern part of the city of Rio de Janeiro. The siting of the park took advantage of an area that was full of old electric power lines. Madureira had about 50,000 residents, but less than 1 square meter of green space per resident (the Brazilian Urban Forestry Society recommends 15 m2 per person). Madureira Park has an area of 93,000 m2 with native trees, pergolas, and reflecting pools that ensure shade and humidity. However, both Duarte and Monteiro criticize the lack of shade and the choice of tree species, saying there are too many palm trees. “Quite a few things were done right at Madureira Park, such as installation of recreational water features, but palm trees, because of the shape of their canopy, don’t provide good quality shade,” she says. “That is why the surfaces of paved areas can get so hot.”

According to Duarte, a positive example can be found in Germany, where urban planning laws stipulate obligations to protect the climate and, since 1976, expressly mention mitigation of the effects of global warming and discuss adaptations to climate change. In Brazil, even the master plans, laws on land use, and the building and construction codes adopted by cities are insufficiently strict on environmental issues, says Duarte.

FAU doctoral candidate in architecture Luciana Schwandner Ferreira, who specializes in green space, says that figures on the number of trees and forested areas can be misleading because they treat as homogeneous what is actually unequal coverage. “Most of the trees in the São Paulo Metropolitan Region are in places like Parelheiros and Cantareira,” she declares, referring to districts far from the city center and its heat islands. In her research, she uses satellite data to measure the impact of the loss of vegetation in recent years on surface temperature, air temperature, and air humidity in the São Paulo Metropolitan Region. Her intention is that the collected data will be delivered to government agencies and can be used to draft directives on forestation in the city.

Project
1. Human biometeorology: analysis of the effects of the environmental variables (meteorological, thermal comfort and air pollution) and climate change on the geriatric population of São Paulo city (nº 2010/10189-5); Grant Mechanism Research Grant – Thematic Project; Principal Investigator Fábio Luiz Teixeira Gonçalves (IAG-USP); Investment R$671,390.00.
2. Participative model for evaluation of comfort conditions in open urban spaces (nº 2015/19484-3); Grant Mechanism Regular Research grant; Principal investigator Alessandra Rodrigues Prata Shimomura; Investment R$121,489.00.

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