January 27, 2023
How do urban plants protect cities from harsh climates?  - 11/13/2021

How do urban plants protect cities from harsh climates? – 11/13/2021

“Urban Permanent Conservation Areas” are guaranteed by law And protect public or private places covered with indigenous or non-native plants. These green areas serve as sanctuaries for animals, including the wild, and play an important role in regulating the “microclimate” of cities and urban centers.

But in addition, this vegetation is closely related to the protection of the population inhabiting the cities. Some urban extremes, such as Sand Storms that hit the western and interior regions of São Paulo and caused heavy rain Floods in New York, has close origins and is partly related to the absence of vegetation in urban centers (and elsewhere).

reverberation Speak with experts and researchers to understand how reducing urban protected areas makes cities more vulnerable.

Does reducing urban protected areas make cities more vulnerable to climate change?

To better understand the problem, imagine any and all areas of vegetation as “weather guards”. Partially and simplified, this is roughly the basic function of all plant life intrinsically. And the less vegetation, the greater the effect of heat in these places, regardless of whether they are protected by law or not.

“There are green areas that are not protected by legislation, but are also important for the local climatic conditions of the city. However, areas protected by law are necessary, because in the absence of such protection, they are more susceptible to removal due to other uses”, points out Dennis Duarte, Member of the Alliance for Science and Society and Professor at the USP Laboratory of Environmental Comfort and Energy Efficiency.

Duarte explains that the loss of vegetation leaves the city at risk of exacerbating irreversible environmental conditions. “The city is becoming more and more watertight and removing these urban oases needed for drainage. It’s an irreparable loss, which translates to overheating, flooding and water that only goes to surface drainage,” he adds.

If there are days when the heat seems unbearable in the city, climatologist and climate change researcher Alexandre Araujo Costa, professor at UECE (Ceará State University), explains why and warns that the change from green roofs to concrete and asphalt increases the impacts from the so-called islands Urban heat, which reduces thermal comfort:

“Urban areas suffer from what we call urban heat islands, so if we take into account global warming, which tends to produce higher temperatures, like heat waves, we amplify this whole scenario,” says the researcher. reverberation.

How does vegetation help the climate of cities in practice?

see o Paris Agreement [que visa impedir o aumento de 2º C na temperatura global em relação à era pré-industrial] Taking into account only the average temperatures recorded in large urban centers around the world, the climate of some cities, such as São Paulo, will be far from complying with what is stipulated: the thermometers in these places have already set He doubled that limit about three years ago.

“This is not just a future forecast: the data indicate that since the middle of the 20th century there has been an increase in the average temperature from about 3 °C to 4 °C in São Paulo, with the exacerbation of these urban climatic conditions, which are replicated in other cities in the world,” Duarte warns.

A street thermometer shows a temperature of 39 degrees Celsius in the city of São Paulo in a photo taken in September 2020


It is precisely the afforestation of cities (including urban protection areas) that helps soften the climate of megacities. “A wooded city is better able to have a natural cooling system, not only because of the shading with the trees, but also because of the ability of these plants to produce evapotranspiration, which is the loss of water from the plant through transpiration,” Costa explains.

The preservation of trees—especially older ones and trees with large crowns—is particularly important for climate regulation, as a custodian of the reverberation, Ana Lucia Turinho, PhD in Ecology and Professor of the Graduate Program in Environmental Sciences at UFMT (Federal University of Mato Grosso).

“Large trees absorb more carbon dioxide during respiration, which will be stored in the body of this plant, preventing it from dispersing into the atmosphere. In this way, we have help lower the overall temperature. If we have this in more cities, it repeats session”.

What is the relationship between vegetation, sandstorms, floods, and the preservation of climate potential in cities? Some phenomena such as floods in New York, caused by the passage of Hurricane Ida, show that Areas like Central Park (overgrown with vegetation) was less affected than others, precisely because of the water flow capacity of the area.

Sep 2, 2021 - Floods inundated vehicles after heavy rain on a highway in Brooklyn, New York, caused by Storm Ida - Ed Jones / AFP - Ed Jones / AFP

Sept 2, 2021 – Vehicles inundated by floodwaters after heavy rain on a highway in Brooklyn, New York, caused by Storm Ida

Photo: Ed Jones/AFP

actually Sandstorms in the interior of Sao Paulo It is a phenomenon known as haboob, which occurs frequently in Asian countries. They are caused by winds and storms touching dry soil and deforestation (in urban centers and elsewhere) and carry the entire waste accumulation into clouds up to kilometers in height. In this case, the vegetation cover again plays an important role in the thermal protection of the soil.

“Part of the plants’ metabolism is some biophysical and chemical change that allows them to absorb part of the solar energy to carry out photosynthesis. Therefore, the surface of trees and leaves are never heated, unlike other urban materials like asphalt,” Duarte notes.

Costa recalls that the loss of green space in cities gives way to completely impermeable areas and this situation creates a new risk variable for these urban centers: “An atmosphere with more water vapor leads to the formation of heavy rain, as well as extremes of heat, which The probability will increase on these occasions and can cause floods and floods. The climate scientist explains that maintaining green spaces facilitates the infiltration of water into the soil and increases the resistance of cities to extreme weather events.”

Deforestation as a whole is already bringing serious warnings about climate change. A study of Brazilians was recently published in the International Journal Earth and Environment Communications The Amazon Forest Project notes that the progress of deforestation could expose 12 million people in the northern region of the country to an intolerable level of heat stress due to their reduced ability to adapt to the effects of climate change.

Duarte recalls that maintaining vegetation mitigates harsh climatic conditions and contributes to a decrease in temperature and surface air. “On a very hot day, people experience a state of heat stress, which has limits to the human body. And there is a negative impact on the health of those who are exposed to these extreme local climates, increasing the chances of some cardiovascular diseases and strokes,” the comments.