The storms that have hit Bahia, Minas Gerais, São Paulo and now Rio since the end of last year were followed by two types of reaction.
The first is pain and anger, for the lives lost because of disasters, but it is also quite common to hear that these extreme events are because of climate change.
But can it be said? Or are they the same old summer storms?
The answer is halfway there, according to experts heard by BBC News Brasil.
That’s because, yes, at this time of year, very heavy rains usually occur.
But at the same time, the frequency and intensity of extreme weather events is increasing, according to available scientific data.
Meteorologist Josélia Pegorim, from Climatempo, explains that these storms are a result of a weather phenomenon known as the South Atlantic convergence zone.
These zones form when moisture brought by winds from the Amazon meets a cold front coming from the south.
This causes the charged clouds to be concentrated in a region until they flow into thunderstorms.
“Practically every year we observe the formation of these convergence zones, with greater or lesser intensity. It’s nothing new, you can’t say that it’s a new phenomenon that climate change is causing”, says Pegorim.
Combination
The meteorologist makes one caveat, however: the convergence zones explain the storms in Minas, São Paulo and Bahia, but in the case of Petrópolis, it was a different and exceptional event.
“The other events of heavy rains that we had were rains that accumulated in a few days, there were several episodes of intense rain. There were several events of convergence zones acting in the same region over the course of weeks. In Petrópolis, it rained in three hours longer than the historical average for the entire month”, says Pegorim.
The meteorologist says that there was a “perfect combination” of climatic factors in the city of Rio de Janeiro.
The air was already damp from a cold front that had passed. Winds off the ocean brought even more moisture. And the meeting of this cooler air with a mass of warm air in the mountain region favored the formation of clouds.
To complete, the mountainous relief caused the humid winds to climb the slopes of the mountains and leave the clouds even more loaded.
Estael Sias, a meteorologist at Metsul, agrees that the rain that hit Petrópolis was unusual because of its intensity in such a concentrated area, but says that this is not surprising.
Sias explains that the encounter between cold and hot air masses is often the trigger for the formation of clouds with “explosive” potential.
The relief of this area of Rio also contributes to heavy rains.
“You don’t have to go far, in recent decades, the mountain region has had storms, landslides and deaths”, recalls the meteorologist.
She especially mentions the rains of January 2011, which left more than 900 dead in Petrópolis, Nova Friburgo and Teresópolis.
But Sias believes that the occurrence of a sequence of such intense rains in such a short time, along with other extreme weather events, is a sign of climate change.
“There were sandstorms last year, very strong heat in the south of the country this year, floods in Tocantins, intense droughts. When we look at all this together, it can be considered an indication”, says Sias.
Climatologist Carlos Nobre says it is rare for climate change to trigger events never seen before.
The most common is to see extreme phenomena like these increasingly intense and frequent.
“Just look at the scientific reports and see that the frequency of heat waves is three to four times greater than 150 years ago, the heavy rains that cause disasters have become more frequent, forest fires and droughts, we have broken temperature records. all this is happening because of global warming”, says Nobre.
The scientist believes that what causes the tragedy is not exactly the occurrence of storms, but the fact that many people live in risk areas and continue to live there even after tragedies like the one in 2011, for example.
Today, says Nobre, 5 million Brazilians live in risk areas. “This is not trivial,” says the climatologist.
“What we see today happens in the midst of an increase of just over 1 degree in the planet’s temperature and, even if we are very successful with environmental policies, it will still rise more, so we need to put it into practice policies to be more resilient to these natural disasters, and the best one is not letting people inhabit risk areas.”
