Saving Carnival, Saving Lives: Inside Rio’s Heat Response

Rio de Janeiro’s heat usually draws crowds to the beach. But in November 2023, it filled clinics and emergency rooms.

The city felt like stepping into an oven. By mid-month, thermometers read 107°F/42°C, with a “real-feel” close to 140°F/60°C. At that temperature, the body’s defenses collapse: sweat refuses to cool, hearts gallop, and heat seeps inward, undoing us cell by cell.

The city itself buckled. Workers abandoned outdoor routines to crowd into air-conditioned towers. Power grids groaned. Street vendors disappeared. Children and grandparents plunged into fountains, chasing relief in the spray.

People gave Rio a new name: Hell de Janeiro. And the cruelest part: summer hadn’t even arrived.

On November 17, during a Taylor Swift concert, a 23-year-old fan collapsed and later died, her lungs and heart overwhelmed by heat exhaustion. Even Swift herself, seen gasping on stage, seemed to falter under the same invisible weight.

She was not the only victim. Researchers estimate the heatwave claimed nearly 1,400 lives in that single month.

And this is just the beginning. Each new record-breaking heatwave, driven higher and faster by climate change, will push health systems further past their limits.

Building a System for People to Thrive

Rio already had protocols for floods and heavy rains. But not for heat. It took the devastation of November for officials to face what had long been clear: heat is no longer just a feature of the city. It is a lethal threat.

“Recognizing this new reality, we brought the issue to the mayor, who promptly created a working group,” recalled Marcus Belchior, then CEO of the Rio Operations and Resilience Center (COR).

For the first time, policymakers, climate scientists, and healthcare leaders sat at the same table with a singular goal: to design a system that could warn residents of deadly heat — and give them a fighting chance against it.

“Heat has gone from being just a characteristic of the city to becoming a health risk,” said Gislani Mateus, Rio’s Municipal Health Secretary. “The work in Rio is driven by the risks at hand.”

That work is coordinated from inside a glass-walled office tower in Cidade Nova, Rio’s “New City.” Here sits the Centro de Inteligência Epidemiológica (CIE), the nerve center of the city’s new heat response.

Originally founded in 2022 to track Covid-19 cases and vaccine coverage, the CIE has since evolved into Rio’s central hub for health and climate surveillance. It integrates streams of data from births and deaths to hospital visits and weather sensors, turning them into actionable intelligence. Now, heat is one of its most closely watched threats.

Officially launched in June 2024, Here’s how the Extreme Heat Response Protocol works: Meteorological stations and sensors across Rio track weather conditions, while the CIE integrates this with health metrics like hospital admissions and clinic or emergency visits. The result is an early warning system that can model risk up to three days ahead and trigger alerts when danger looms.

Alert systems are only possible through data — data that give cities the opportunity and time to act and prepare. Being able to predict heat indices, forecast health impacts, and trigger responses in advance was a key part of the process.
Gislani Mateus
Rio de Janeiro Municipal Health Secretary

The Initial Test

The system faced its first real challenge during the pre-Carnival of 2025, Rio’s weeklong festival of parades, music, and dancing. The celebration coincides with peak heat season, and this year climate models predicted extremes. The question was not just how hot would it get? but how could millions of revelers be kept safe?

When models warned of mounting risks, the CIE activated its second-highest heat protocol for the first time, a level linked with a 50% increase in mortality among older adults and people with chronic conditions.

Within hours, phones buzzed across Rio as thousands of residents received WhatsApp and text alerts warning them of the risk and offering advice on how to stay cool. At the same time, the city opened cooling centers, stocked clinics to serve as hydration hubs, and deployed emergency services.

“The city showed that it can protect lives without losing its identity,” said Mateus. “Carnival could go on, but with adaptation measures.”

Still, she added, cultural change remains a challenge. “It used to be appealing to talk about Rio hitting 40°C, everyone sunbathing on the beach — it’s part of Rio de Janeiro’s character,” said Mr. Belchior, COR’s then CEO.

Now, in a world transformed by climate change, that boast has become a warning. How the city responds may well decide its future — and offer a lesson for communities across the warming planet.

But the truest measure of resilience wasn’t in the parade routes or cooling centers downtown. It came in the favelas, where heat bites hardest, and resources run thin.

On the Frontlines in Rocinha

A primary health care clinic in Rocinha, Rio de Janeiro.

Among Rio de Janeiro’s more than 1,000 favelas, Rocinha is the most densely populated — 72,000 people living within less than a square mile, served by three primary health clinics.

Marcus Adams, a coordinator at one of them, described the strain: “Each team is the first point of care for 3,000 people. When people are sick, when they need a prescription, when they need an exam, when they need a referral, or when they simply want to talk to someone, they come to the clinic. So usually these services are overloaded.”

Heatwaves compound the pressure. With water and power outages common, residents often lack air conditioning, fans, or even steady access to drinking water.

“When heatwaves happen, illness increases a lot — especially infectious diseases, diarrhea, vomiting,” Adams said.

That’s where Rio’s new warning system has mattered most. When alerts go live, clinics like Rocinha’s prepare air-conditioned rooms, stock oral rehydration solutions, and send mobile teams to check on bedridden elders and small children.

“Since the protocol was implemented, we’ve been able to be ready in advance,” Adams said. The clinic doesn’t simply wait for people to come. “We also have a team that goes out on the streets, looking for people who are most vulnerable during heatwaves — the elderly, bedridden, and small children.”

Cities Leading the Way

What happened in Rocinha reflects a larger truth: climate resilience will be won or lost in city neighborhoods. By 2050, more than two-thirds of humanity will live in urban areas. And as global agreements falter, it is often cities that lead.

Rio is part of C40, a coalition of nearly 100 mayors worldwide committed to local climate action. Its pilot project includes “cool corridors” in the city’s hottest neighborhoods — temperature sensors, cooling furniture, and vegetation — along with guidelines for replication elsewhere. Plans are also underway to expand cooling centers and refine neighborhood-level alerts.

“It’s very important for cities to be in the big conversations. It’s where most people live,” said Mateus. “We hope Rio de Janeiro’s work will resonate with other cities. Because today, heat is a risk that involves all areas of city life. It’s one health — environmental health, human health. Everything is connected.”