Research reveals increase in extreme air temperature events on the coast of Brazil

It's getting hot and it's not just print. An unprecedented study carried out by the Federal University of São Paulo (Unifesp) with the support of the São Paulo State Research Support Foundation (Fapesp) evaluated heat waves along the Brazilian coast by the variation in the intensity and frequency of extreme heat events. temperature. The research shows that it is becoming more common to find increasingly higher temperatures on the southeast and southern coast of the country.

The study evaluated a historical series with air temperature data observed every hour of the day over the last 40 years in five coastal regions of the country: MA (São Luís), RN (Natal), ES (São Mateus), SP ( Iguape) and RS (Rio Grande). Based on these data, the four researchers from the Instituto do Mar (IMar/Unifesp) involved used mathematical models to define what temperature extremes would be for each of the regions, because in a country as large as Brazil and with such a diverse climate, A given temperature may be extreme in one region and normal in another. Furthermore, different temperatures can be considered extreme depending on the month of the year in each location.

With this detailed research, it was possible to observe how the frequency and intensity of maximum and minimum temperature values, the variation in thermal amplitude throughout the day and the abrupt changes in temperature between consecutive days vary in each region and time of year. The study "The increase in intensity and frequency of surface air temperature extremes throughout the western South Atlantic coast" was published this Tuesday, 25/04, in the magazine Scientific Reports of the group Nature, one of the most prestigious scientific journals in the world, and which was the fifth most cited journal worldwide in 2021.

Occurrences of extreme temperatures and heat and cold waves

Extreme hot or cold temperature events are part of the world's climate reality. However, the effects of climate change are visible and alter this pattern. "One of the practical examples of climate change is the increase in the intensity and frequency of extreme hot and cold temperature events. An extreme temperature occurrence occurs when a given maximum or minimum temperature exceeds an expected 'threshold' characteristic of the region. A heat or cold wave corresponds to an extreme event and is characterized by a period of a few days with maximum temperatures higher or minimum temperatures lower than the expected limit for the time of year", explains William Conti, researcher at IMar/Unifesp and responsible for modeling mathematics of the data obtained in the research.

How to define this 'limit' in time and space was the main objective of the study. Does a temperature extreme in the south of Brazil and in the north of the country have the same value? Are these limits changing over the years? And within the same year, can a given temperature be extreme in one season of the year but not in the others? And, on a smaller temporal scale, how is the variation in maximum temperatures on consecutive days? And what is the difference between maximum and minimum temperatures on the same day? These were the guiding questions of the research carried out by Unifesp researchers who evaluated seasonal and daily patterns. These impacts were measured in terms of occurrences (days in which an extreme occurred) and events (days following the occurrence of extremes, characterizing a wave).

The study showed that the entire Brazilian coast is already suffering some impact from climate change in relation to air temperature, with the coasts of the Southeast and South regions being more impacted than the North and Northeast regions where, despite there being temperature extremes around the Throughout the year, they are not increasing in frequency or intensity.

However, in the Southeast and South of the country, the scenario is different. On the coasts of RS, SP and ES, the frequency of daily occurrences of maximum temperature extremes and heat waves, characterized by consecutive days of maximum temperature extremes, has increased over the years. Furthermore, the frequency of daily occurrences and cold wave events in ES has increased. "These data show how the Southeast and South regions of Brazil are already experiencing impacts from air temperature that will affect biodiversity and even the economy", highlights Fábio Sanches, author of the research and post-doctoral fellow at IMar/Unifesp. "We identified the coast of ES as the most affected region among those we studied, because in addition to heat waves, it was the only region where the frequency of cold waves is increasing", explains Sanches.

In addition to the frequency of events in the Southeast and South, data on the intensity of extreme minimum temperatures caught the attention of researchers: on the coast of RS, the lowest temperature (extreme cold) is increasingly higher. "This means that it is getting less and less cold in the south of the country, which could have impacts on agricultural production and even tourism", analyzes Ronaldo Christofoletti, research coordinator, CNPq productivity fellow and professor at IMar/Unifesp.

In the last 40 years, the occurrence of extreme temperature events has almost doubled in SP (84%), doubled in RS (100%) and almost tripled in ES (188%). The number of events per year varies, depending on specific conditions such as phenomena El Boys e La Girls, but, if we consider an average, in ES, the rate of increase in extreme events is, on average, 4,7% per year, while in SP it is, on average, 2,1% and, in RS, of 2,5% per year.

“The changes in the patterns of extreme events on the Brazilian coast are an important warning sign for the climate vulnerability of Brazil as a whole. This study confirms that the climate emergency is not futurology but part of a reality that we have to face, combating its causes with concrete mitigation actions and effective public adaptation policies”, warns Ana Toni, national secretary of Climate Change at the Ministry of Environment and Climate Change (MMA).

Climate stability: temperature amplitude throughout the day and sudden temperature variations between consecutive days

In addition to evaluating the maximum and minimum temperature extremes, the researchers evaluated two other factors: first, the possible variations in thermal amplitude throughout the same day (Tmax - Tmin), and then whether there were 'abrupt' changes in temperature, the from the comparison of the maximum or minimum temperature between consecutive days. For these indicators, the research showed that the entire Brazilian coast experiences climate change. "Understanding the daily temperature range and also the temperature variations between consecutive days is important to understand climate dynamics and their potential impacts, such as the arrival of cold fronts and also rainfall regulation", highlights Fernando Martins, professor at IMar/Unifesp and climate dynamics researcher, as well as a CNPq productivity fellow.

The RN region was the only one that did not show variations in daily thermal amplitude. However, it is increasingly common to find days with greater thermal amplitude in Maranhão. Furthermore, the state of MA was the only region that demonstrated an increase in the number of consecutive days with greater thermal amplitude.

In the Southeast and South, thermal changes are even greater. In addition to the increase in the frequency of days with greater thermal amplitude, the regions of ES, SP and RS showed an increase in the intensity of daily thermal variation, which means that it is increasingly common to find days that are increasingly variable in temperature. "Different from heat and cold waves that indicate extreme temperature situations, daily thermal amplitude data indicate temperature changes over hours that are more associated with our thermal comfort throughout the day", highlights Sanches.

When evaluating the abrupt changes in temperature between consecutive days, the pattern on the Brazilian coast was reversed, with MA and RN showing more impacts than the Brazilian Southeast and South. In MA and RN, an increase in abrupt changes in both maximum and minimum temperatures was observed on consecutive days, and in MA, it was also observed that the number of consecutive days in which maximum temperatures vary greatly between days is increasingly frequent .

The ES, which had presented many impacts regarding heat waves, cold waves and daily thermal amplitude, did not present any impact when analyzing the variations between consecutive days. For SP and RS, there is an increase in the frequency of events where the maximum temperature between consecutive days is very variable. "Understanding temperature variations on the same day and between consecutive days has a direct relationship with physiological impacts and even public health, as many respiratory diseases and our sense of well-being are associated with temperature variations", recalls Christofoletti .

The impacts of temperature variations

"The increase in heat and cold waves has several impacts on society around the world, ranging from thermal discomfort to an increase in forest fires, health problems and mortality of animals, plants and humans, especially, elderly people and people in vulnerable situations. Recent studies demonstrate an increase of almost 70% in the mortality of elderly people due to intense heat. Over the last few years, there have been several cases of mortality due to heat waves as seen in Spain, Canada and Portugal, for example", reports Christofoletti.

The impacts of temperature variations also impact biodiversity. "Several species of marine animals have shown physiological changes, changes in behavior and even in the distribution of where they live due to heat and cold waves. Extreme temperature events can cause mass mortality of fishing resources and influence fishing chains, especially artisanal fishing", says Sanches.

In addition to fishing resources, Christofoletti points out that "Brazilian agribusiness is threatened by these variations. Productivity is dependent on the annual cycle of temperature and rain, and changes in extremes and thermal amplitude can lower productivity, the quality of production or even lead to crop loss. Especially in the south of the country, with data that minimum temperatures are increasingly hotter, this could lead to a change in the production system in the coming decades".

The variation in temperature extremes and also in daily thermal amplitude and on consecutive days can intensify extreme rain events, such as those seen on the coast of São Paulo in 2023. "The rainfall regime is associated with air temperature, evaporation, sea temperature ocean and atmospheric pressure systems that produce winds. The dynamics of meteorological conditions associated with extreme events or abrupt changes between consecutive days are likely to influence the volume and intensity of rainfall and can lead to tragedies such as those that occurred on the north coast of São Paulo in February, which was the result of very hot days, a warmer ocean, greater evaporation of water and air masses and winds that reached the coast", details Martins.

"Our study demonstrates for different regions of the Brazilian coast how heat waves, cold waves and daily thermal amplitude are varying. This data allows future steps to understand the influence of these variations on agricultural indices -- for example: agricultural production of regionally important species --, public health -- such as the increase in cases of respiratory problems or mortality among the elderly during periods of extreme weather --, and the importance of local, regional and national public policies", says Christofoletti.

"The Federal Government has highlighted the importance of climate resilience and municipal and state plans to combat climate change. To achieve this, it is essential to know how climate change is already impacting each region, as our study contributes", adds Christofoletti.

However, a challenge was highlighted by the team of researchers: "climate change studies require historical and continuous monitoring data. To understand the current situation of extreme events and to predict future scenarios that assist in coastal resilience plans, it is urgent that we expand meteorological data monitoring stations on the Brazilian coast. Research like this requires long time series of continuous and highly reliable data. Municipal and state governments must expand monitoring stations in the regions. The installation and monitoring costs for these governments are certainly lower than the expenses needed to subsequently recover the impacts of extreme events on the economic and public health sectors", comments Sanches.

"In addition to ensuring that local and regional data are continuously obtained, it is essential that they are freely accessible to society and universities. Many research in partnership between local governments and universities can help to understand the local climate and strengthen actions in the municipalities", says Sanches.

With the data currently available for the indicated municipalities, the research evaluated the variation over the last 40 years that reflects nearby regions. "One of the differences of our study is providing information that shows what is possibly an extreme in each month at the current moment. Understanding the limitations of the data is also an important step", indicates Conti.

"First, extreme values ​​are considered according to the temperature patterns of the year and recent periods. Therefore, in long time series, they vary over the years, so continuous monitoring is essential [detailed examples below]. Second, When thinking about extreme values, many people only look for the extreme maximum and minimum of the year. However, it is important to understand these values ​​on a monthly basis. Sometimes, in the Southeast and South, we will have a temperature value in July that is not an extreme for the year , as lower maximum temperatures are expected at this period of the year than in January. However, this given temperature could be extreme for that month of July and bring impacts to animals and crops at that time", compares Conti.

Extremes in temperature

As research has shown, extreme values ​​vary over the years. However, for reference purposes in 2023, the researchers indicated the maximum and minimum values ​​for the entire period and the current values ​​that, possibly, can be considered as extreme temperatures on the coast of each region based on the median of extreme temperatures in each month of 40 years of data. These values ​​have a regional influence depending on the cities where the weather station is located.

Current temperature limit values ​​for which values ​​above Tmax or below Tmin can be considered extremes of heat or cold, respectively. It should be noted that these values ​​are for the current moment and will vary over the next few years due to the impacts of climate change.