Heat wave It is an atmospheric phenomenon characterized by the abnormal increase in temperatures in a given location compared to the maximum temperatures considered normal for that area. Heat waves are caused by high pressure systems that temporarily stop hot air from moving, which can remain that way for a few days. Its occurrence may be associated with factors such as the approach of cold fronts and El Niño. In addition, the increasing frequency with which Brazil and the world suffer from heat waves indicate the role of climate change in extreme weather events.
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heat wave summary
Heat wave is an atmospheric phenomenon characterized by the abnormal increase in temperatures in a given location.
During heat waves, recorded temperatures are higher than the maximum temperature considered normal for the period of the year.
They are caused by installing a high pressure system over an area, which causes hot air to be trapped.
The dynamics of air masses, El Niño and climate change are factors that act or interfere with the occurrence of heat waves.
A heat wave lasts approximately three to five days and may vary.
They cause changes in atmospheric weather, such as a reduction in cloudiness and an abnormal increase in temperatures.
Heat waves harm human health, causing deaths, overloading electrical systems, impacting the economy and are very harmful to ecosystems.
Heat waves have been increasingly recurrent in Brazil and in the world. The most recent of these took place in 2023.
What is a heat wave?
Heat wave is the name given to a change in atmospheric weather characterized by the sudden increase dthe temperatures of one locality. This increase is caused by the arrival of a warm air mass, which results in intense heat and can cause changes in the relative humidity. Heat waves correspond to unexpected changes in the temporal conditions of an area and bring with them the occurrence of abnormal or even extreme temperatures for the period of the year (season) and for the locality in question.
Causes of the heat wave
Heat waves are mainly caused by installation of a high pressure system in a given area, which means that the hot air hovering over it, as well as the air close to the surface, cannot move or leave this system. Therefore, the air is said to be trapped. This trapped air continues to be heated, which causes sudden and anomalous increases in temperatures. In more urbanized areas, where concrete surfaces are more abundant, the intensity of heat waves is even greater.
duration of heat wave
The duration of a heat wave is variable and depends on the dwell time of the high pressure system. In general, hot flashes last between three and five days over a region.
Heat wave incidence
The incidence of heat waves around the planet has occurred with increasing frequency in recent decades. Two factors interfere with the occurrence of this atmospheric phenomenon and its incidence in increasingly shorter intervals of time:
Arrival of cold front: A cold front forms when a cold air mass meets and pushes against a warm air mass. The surface of contact between masses of different appearance is called the front. The air mass with high temperatures moves to other areas, causing significant changes in atmospheric weather. It is common that, before the arrival of a cold front, an area experiences a sudden increase in temperatures precisely for this reason. To better understand the dynamics of the cold front, click here.
El Niño: is the abnormal heating of the surface waters of the Pacific Ocean in the equatorial region of the planet Earth, that is, in low latitude. This increase in temperatures alters the circulation of the atmosphere on a global scale. Due to El Niño, some locations begin to experience very hot and dry weather, as is the case in the North and Northeast of Brazil, in addition to the Center-West and Southeast, where the behavior of the atmosphere may vary with each new occurrence of El Niño. To learn more about this phenomenon, click here.
Climate changes: global warming and the resulting climate changes have made extreme atmospheric events, such as very intense heat waves, increasingly frequent on our planet. These changes are the direct result of anthropic action, that is, of human activities, such as the emission of polluting gases into the atmosphere.
Effects of the heat wave on time
![Thermometer reading 41º C in the city of São Paulo (SP) during a heat wave that hit Brazil in 2012.[1]](/f/3360d754370800cc07ed23dae6fdb9e7.jpg)
A heat wave is responsible for causing changes in the atmospheric weather in the area where it is installed, since it is a matter of periodic changes that will soon dissipate. As we saw earlier, in a matter of a few days the heat wave ceases to be in force and gives way to milder weather conditions.
O increase in local temperatures is the main change caused by the heat wave. It is estimated that, when this phenomenon occurs, temperatures are recorded up to 5 ºC higher than the maximum temperatures that would be considered normal for a given region. This variation is observed for more than one day, and only after that it is possible to classify the change in temperatures as a result of the duration of a heat wave. When associated with a mass of air hot and dry, the heat wave also causes drop in relative humidity.
The high pressure systems that cause heat waves also prevent the cloud formation in the sky. For this reason, the period of duration of heat waves is marked by clear sky and the direct arrival of the sun's rays over the earth's surface, which helps to further intensify the heat and thermal sensation of the area.
Check out our podcast: What is important to know about climate factors
Consequences of the heat wave
The high temperatures of heat waves reflect on the functioning of the human body, on the well-being of the population, on the economy and also on the environment. The way heat waves interfere in the human body and in nature depends on their intensity and the time they remain over a region.
They are consequences of heat waves for humans:
exhaustion and tiredness caused by exposure to extreme heat;
dryness and heating of the skin, as well as the appearance of irritations;
accentuation of heart and respiratory diseases;
headaches and irritability;
fainting;
dehydration;
insolation;
death from hyperthermia.
In areas such as economics and especially in the environment, the intense heat resulting from heat waves has the following consequences:
increase in outbreaks of fire in woods and forests, which can spread with the occurrence of winds and in case of dry vegetation;
death of animals, causing loss of biodiversity;
loss of crops and livestock;
overload of electrical power systems, which can cause blackouts and rationing, as well as other urban infrastructure, such as water supply.
Brazil heat wave
The heat waves are increasingly recurrent atmospheric phenomena in Brazil. In 2023, the country was hit by a strong heat wave during the winter, a season in which milder temperatures are recorded in almost all regions of the country. With the advance of the heat wave across the territory, states in the Southeast and Midwest regions were the most affected, along with part of the North and Northeast, where the variation was equal to or greater than 5º C.
Cities in the Southeast, such as the capitals São Paulo and Rio de Janeiro and areas of the state of Minas Gerais, experienced heat from 37.5º C to 41º C in the winter heat wave of 2023. The two aforementioned cities registered record maximum temperatures for the month of August.
Temperatures above 39º C were also recorded in cities in the Northeast, such as Bom Jesus do Piauí (PI), which reached a maximum of 40º C, and Formosa do Rio Preto (BA), with 39.7º C. It should be noted that Bom Jesus do Piauí has already experienced other heat waves as intense as the most recent one. In 2005, the city of Piauí recorded a temperature of 44.7º C in the month before summer. A year later a similar figure was recorded for the same period.
In the North region, where air humidity is very high, the heat wave resulted in a thermal sensation of 49º C. In reality, there were few locations that did not feel this enormous thermal variation caused by the heat wave. Most of them are concentrated in the extreme south of the country.
In 2023, El Niño is pointed out as the main causefor the heat wave in Brazil. As catalysts for its occurrence, meteorologists also cite the advance of a polar air mass, since the occurrence is occurred during the winter, and the effects caused by climate change, with the recurrence of extreme atmospheric events.
It is important to remember that this was not the first heat wave to hit Brazil. A Midwest region of the country experiences this type of phenomenon with some frequency, especially in the summer months. Between 2020 and 2022, many cities in Mato Grosso and Mato Grosso do Sul recorded the occurrence of temperatures equal to or greater than 40º C, reaching 44º C in Cuiabá (MT) and 44.4º C in Águas Claras (MS) in the year 2022.
Read too: La Niña — the opposite acting phenomenon to El Niño
heat wave around the world
As in Brazil, very intense heat waves have occurred in other regions of planet Earth. Territories in Europe, such as France, Italy, United Kingdom, Spain and Greece, North America, such as United States, as well as Asia, such as China, recorded above-normal temperatures for the summer of 2023. The values vary between 34º C and 48º C, since in many of these locations the maximum temperatures are considered low when compared to the tropical regions of the globe.
To the intense heat waves around the world have became more and more frequent. Over the past ten years, countries like Argentina, Australia, India, Canada, Japan and Russia have recorded some of their highest temperatures, breaking historical records. To get an idea of how these phenomena worsened, in northeastern Siberia, the coldest region of Russian territory, temperatures reached 38.9º C in 2021. Maximums in this area are usually 24º C.
According to the World Health Organization (WHO), the direct effects of heat waves caused the death of 166,000 people in the period from 1998 to 2017. Another alarming data is that, in 2015, around 175 million people were exposed to a wave of heat for the first time, which means that this type of occurrence has reached more and more regions of the world.
Heat wave exercises
question 1
Read the following excerpt, which is part of a meteorologist's speech about winter in Brazil in 2023:
"This level of heat during the winter is highly unusual, considering that temperatures generally are lower in this season, with averages of 20 to 25 degrees, mainly in the South and Southeast regions", it says.
PEIXOTO, Roberto. 'Highly atypical': meteorologist explains causes and duration of heat wave that gains strength in Brazil. G1, 23 Aug. 2020. Available in: https://g1.globo.com/meio-ambiente/noticia/2023/08/23/altamente-atipico-meteorologista-explica-causas-e-duracao-da-onda-de-calor-que-ganha-forca-no-brasil.ghtml
The atmospheric phenomenon he refers to is called:
a) tropical air mass
b) warm front
c) heat wave
d) cold
e) orographic rain
Resolution: Alternative C. The meteorologist comments on an abnormal increase in temperatures during the winter, which characterizes the arrival of a heat wave.
question 2
Heat waves are atmospheric phenomena that occur when a high pressure system settles over a certain area, trapping hot air. With climate change, its occurrence has been increasingly frequent in Brazil and worldwide. In addition to this, there are other factors that contribute to the occurrence of heat waves, one of them being:
a) trade winds
b) monsoon rains
c) alternation between seasons
d) El Nino
e) absence of rain and drought
Resolution: Alternative D. The warming of the waters of the Pacific Ocean, a phenomenon known as El Niño, causes periodic changes in the atmospheric circulation and contributes to the formation of heat waves.
Image credits:
[1]Nelson Antoine / Shutterstock
Sources:
CASEMIRO, Poliana. Heat wave: learn how El Niño and global warming caused the temperature to rise in the country. G1, 23 Aug. 2023. Available in: https://g1.globo.com/meio-ambiente/noticia/2023/08/23/onda-de-calor-saiba-como-o-el-nino-e-o-aquecimento-global-fizeram-a-temperatura-subir-no-pais.ghtml.
COHEN, Patricia. Economic consequences of extreme heat will get worse over time. Folha de S.Paulo, 19 Jul. 2023. Available in: https://www1.folha.uol.com.br/mercado/2023/07/consequencias-economicas-do-calor-extremo-vao-se-agravar-com-o-tempo.shtml.
GRANCHI, Julia. Heat wave: Can Brazil suffer from an extreme summer like the Northern Hemisphere? BBC News Brazil, 29 Jul. 2023. Available in: https://www.bbc.com/portuguese/articles/c0dkr9epnwdo.
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THE GLOBE. Heatwaves: What they are, what causes them and why Europe suffers so much from them. O Globo Newspaper, 21 Jul. 2022. Available in: https://oglobo.globo.com/blogs/blog-do-acervo/post/2022/07/ondas-de-calor-o-que-sao-quais-as-causas-e-por-que-a-europa-sofre-tanto-com-elas.ghtml.
PEIXOTO, Roberto. 'Highly atypical': meteorologist explains causes and duration of heat wave that gains strength in Brazil. G1, 23 Aug. 2020. Available in: https://g1.globo.com/meio-ambiente/noticia/2023/08/23/altamente-atipico-meteorologista-explica-causas-e-duracao-da-onda-de-calor-que-ganha-forca-no-brasil.ghtml.
THOMAS, Jennifer. Hot flashes: understand why they occur. One Planet, 07 sep. 2021. Available in: https://umsoplaneta.globo.com/clima/noticia/2021/09/07/ondas-de-calor-entenda-por-que-elas-ocorrem.ghtml.
WHO. Heatwaves. World Health Organization, [n.d.]. Available in: https://www.who.int/health-topics/heatwaves.
Source: Brazil School - https://brasilescola.uol.com.br/geografia/onda-de-calor.htm
