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Urban heat island, 1.5 ºC warmer than its surroundings

Urban heat island, 1.5 ºC warmer than its surroundings

The urban heat island phenomenon is a consequence of the urbanization of the earth and is defined as the difference in temperature between the city and its undeveloped environment. These impacts take on special relevance in a world in which more and more people live in metropolises: in Argentina, more than 90% of the population lives in cities.

A study determined this average value after analyzing the temperature of 33 cities in our country and established the main causes of the phenomenon. They warn about its consequences and propose interventions to achieve more sustainable cities.

An investigation by the UBA determined that Argentine cities are 1.5 ºC hotter than their surroundings at night and 0.72 ºC during the day, on average. This value emerged after measuring and comparing the temperatures of 33 urban centers throughout the country, with their non-urbanized environments. This phenomenon, called 'urban heat islands' (ICU), is one of the many impacts that urbanization of the earth has on its inhabitants and acquires a special relevance in a context in which the national urban population exceeds 90% of the population. total. In this sense, the scientists established the factors that explain this thermal event, warned about its consequences and proposed interventions to plan the metropolises.

“We studied the 33 largest cities in the country, which are very different from each other due to their population, temperatures and rainfall. We analyze from Jujuy to Trelew and from Mendoza to La Plata, and we differentiate between day and night in all seasons of the year ”, commented Paula Casadei, who carried out this study as part of her degree thesis for the Bachelor of Environmental Sciences (LiCiA ) of the Faculty of Agronomy of the UBA (FAUBA).

In this context, he added: “At night, the difference in heat between cities and their surroundings was always positive, with a general average of 1.5 ° C. During the day, the differences had positive and negative values, but with a positive annual average of 0.72 ° C. In Oberá, in the province of Misiones, the ICU effect reached 4.3 degrees ”.

Heat islands

Martín Garbulsky, professor at FAUBA, researcher at the Institute for Physiological and Ecological Research Linked to Agriculture UBA-CONICET and director of Casadei's thesis, explained: “In Oberá it was urbanized on an area that originally resembled a jungle. That is, we removed a very dense green coverage to put sheet metal roofs, cement constructions and asphalt roads. These materials retain and reflect much more energy than the original coating, an energy that is released daily throughout the 24 hours ”.

For researchers, urbanization is the most extreme form of land use change and brings multiple impacts on global ecosystems and their inhabitants. ICUs are part of these negative effects. Casadei's research determined the factors that most influence this phenomenon.

“When we analyzed the data, we could see that the context within which cities are immersed influences their temperature much more than their size or population density. Cities established in more humid and vegetated areas have higher ICUs. On the other hand, those that are located in arid areas and with less vegetation have lower ICUs and even negative differences with their surroundings, ”said Casadei.

Cold islands

Martín Garbulsky affirmed that although they thought that cities would always be hotter, the study showed that many function as ‘urban cold islands’ (IFU). “This means that the temperatures inside the city were lower than outside. For example, the city of Mendoza was 4.2 ° C colder than its surroundings. Another example is San Rafael, which was built on something similar to a desert ”.

“The phenomenon may be due to the fact that the vegetation activity is higher within the city than outside it. This is one of the factors that intervenes in the cooling of cities, together with the selection of construction materials, agricultural or livestock activity and the presence of bodies of water, ”said the researcher.

For his part, Casadei added: “It was also interesting to compare cities with similar size and population, such as Resistencia and Corrientes. In this case, we realized how important is the distance to the Paraná River, which is a great modulator of temperature. Resistencia, in Chaco, had an average annual ICU of 3.79 ° C, while the city of Corrientes, located closer to the river, presented an average of 0.35 ° C throughout the year ”.

Sustainable interventions

“It is essential to know the functioning of what we call urban ecosystems, especially in a global context in which more and more people live in cities. With this knowledge we can better plan urban growth. For example, using certain construction materials or increasing the surface of green spaces or creating artificial bodies of water ”, Garbulsky pointed out.

Regarding the consequences of the ICU phenomenon, the teacher said: “High temperatures cause cities to spend a lot of electricity to alleviate its consequences. Better thought, designed and intervened cities could be much more efficient in energy terms ”.

“My thesis work showed that in the last 15 years there has been an increase in the impervious surface, or a lower proportion of green spaces in the cities that I analyzed. In our country, more than 90% of the population lives in urban areas. For this reason, it is essential to approach and understand these places, where the environment and society interact in search of maximum general well-being ”, concluded Casadei.

Video: The urban heat-island effect. Cronkite News (October 2020).