Heat waves: Brazil surpasses 50 days per year of high temperatures

In six decades, the frequency of the extreme event increased; between 1961-1990, the average was 7 days of heat waves

Intense heat waves in Brazil aren’t a rare event anymore. - Miguel Schincariol / AFP

The intense heat wave Brazil faces this week, with temperatures over 40°C in many parts of the country, isn’t a rare event anymore. In the last decade, the occurrence of extreme hot periods has increased, and the number of days in which we face heat waves has surpassed the average of 50 per year.

That is what shows an analysis by the National Institute for Space Research (Inpe, in Portuguese) presented on Monday (13), which considered some changes in Brazil during the last 60 years due to global warming.

According to the survey, between 1961 and 1990 – the reference period for the study – the number of days with heat waves did not surpass the average of seven per year. With the rise in greenhouse gas emissions and, consequently, the global average temperature, they jumped to 20 days from 1991 to 2000, then 40 days in the next decade and reached an average of 52 days between 2011 and 2020.

The increase in the duration of heat waves was identified across the country, but was more pronounced in the North and Northeast regions.

The analysis did not consider indicators of the last three years. However, the tendency is for this increase to continue – even more so considering that 2023 is expected to be, globally, the hottest year on record.

According to the National Institute of Meteorology, the average temperature in Brazil is also breaking record after record. The months of July, August, September and October were the hottest since the beginning of the measurements. The expectation is that the extreme temperatures observed particularly this week across the country will also break all records.

Researchers consider a heat wave a period of at least six consecutive days in which the maximum temperature surpasses at least 10% of what is considered extreme compared with the reference period.

“With these data, we are moving from only realizing the changes to knowing what has happened in Brazil in the last six decades,” said Osvaldo Moraes, the director of the Department for Climate and Sustainability of the Ministry of Science, Technology and Innovation, in a press conference.

Not only are the heat waves increasing in the country, but also the temperature. “We identified a tendency for maximum temperatures to rise with a very significant warning. Between 2011 and 2020, all the Brazilian regions recorded a rise in temperatures over 1.5°C, that is, higher than what was established by the Paris Agreement," explained Lincoln Alves, the researcher at Inpe who coordinated data collection.

He was referring to the commitment signed by almost all the countries in 2015, during the UN Climate Summit, aimed at reducing greenhouse gas emissions to prevent the world’s average temperature rise over 1.5°C compared to the pre-industrial period.

In some parts of the world, particularly in the northeast and central areas, the maximum temperatures between 2011 and 2020 were 3°C above the measurements recorded for the reference period.

According to the analysis, in the reference period (from 1961 to 1990), the average maximum temperature for the region used to be 30.7°C. It rose to 31.2°C between 1991 and 2000, then 31.6°C between 2001 and 2010, and jumped to 32.2°C between 2011 and 2020.

The work also considered rain frequency during the last six decades. In the northeastern and central regions (including some parts of the North, Central-West and Southeast regions), there was a rise in the number of consecutive dry days with rainfall below 1mm. Between 1961 and 1990, there were an average of 80-85 consecutive dry days. Between 2011 and 2020, there were 100 days in the most affected areas.

The rainfall reduction, especially in the Northeast and Central areas of Brazil, was 40%. On the other hand, there was an increase in rainfall in the South region of up to 30%. In the reference period, the maximum five-day rainfall in the region was, on average, around 140mm. This value grew to an average of 160mm.

Evolution of intense rainfall in a five-day period; in the South region, this index went from 140 mm between 1961 and 1990 to 160 mm between 2011 and 2020 / Inpe

The data will be used to develop an adaptation strategy in Brazil as part of the Climate Plan, which is being prepared by the federal government. With this information, the idea is to analyze the possible impacts and vulnerabilities and find ways to adapt cities and regions to the new reality.