- Extreme weather in Rio de Janeiro is getting worse: recent years have brought record-breaking heat and rainfall to Brazil’s second-largest city, intensifying the risk of floods and landslides, particularly in vulnerable urban areas.
- Experts warn of “climate gentrification,” where urban development and inequality amplify disaster risk; more than 20% of Rio’s homes are in high-risk areas, many in precariously built communities on hill slopes or low-lying flood zones.
- Disaster prevention measures exist but fall short; while sirens provide some early warnings, experts stress the need for comprehensive urban reform, nature-based solutions like the “sponge city” design, and greater community involvement to truly mitigate risks.
Judging by the last few summers, Rio de Janeiro’s residents should be preparing for the worst. On March 17, 2024, the neighborhood of Guaratiba, in the city’s West Zone, recorded the highest apparent temperature in the last 10 years: 62.3° Celsius (144.14° Fahrenheit), according to data from Alerta Rio, a system run by the municipal government. On Feb. 20, 2025, the thermometer in Guaratiba hit 44°C (111°F), the highest temperature in the historical series, which began in 2014.
2024 was also the wettest summer in Brazil’s second-largest city since measurements began in 1997. In January, the average rainfall reached 349 millimeters (13.74 inches), surpassing the previous record from 2013 (347 mm, or 13.66 in), and nearly 200 mm (7.87 in) higher than the historical average for the month (161 mm, or 6.34 in).
In other words, the intensity of the rains and the heat has been progressively increasing in recent years in Rio de Janeiro — two manifestations of global climate change with a high potential for disaster. Consider what happened between April and early May 2024 in the city of Porto Alegre, in the southern state of Rio Grande do Sul, where heavy rains caused floods that affected 2.4 million people, with 183 confirmed deaths.
But Rio de Janeiro is no Porto Alegre: Rio has hills. The city sprawls around the bases and creeps up the slopes of three mountain ranges — Tijuca, Pedra Branca and Gericinó-Mendanha — making for thousands of precariously installed homes in defiance of the storms.
A new index developed by Ambiental Media in partnership with the RioNowcast+Green research group, from the Institute of Computing at Fluminense Federal University, reveals that the city of Rio de Janeiro contains at least 599,202 private homes, 21% of the total, located in areas of high vulnerability to disasters resulting from rainfall. Of these, 141,707 are in areas of extreme vulnerability, which combine high susceptibility to flooding or landslides with high socioeconomic vulnerability.
The recipe for disaster is confirmed by the fact that the rains are not only more intense; they are also more poorly distributed throughout the year: shorter and more torrential rains, interspersed with many dry days. According to urban climate planner Pedro Henrique de Cristo, who holds a master’s degree in public policy from Harvard University, “It’s the worst possible scenario, especially for landslides, because the soil, when it doesn’t rain much, becomes compact and dry; and when there’s a heavy downpour, it takes the land away, like a cake crumbling.” In terms of disasters related to landslides, 69,760 homes are highly vulnerable; 9,796 are extremely vulnerable.
Even when the cake itself doesn’t crumble, the icing can run off, pooling at the bottom of the plate: in other words, rainwater runoff can concentrate in the lowlands that spread out at the base of these massifs. Here, there are 530,282 households with high vulnerability to flooding and 131,922 with extreme vulnerability. The index considers socioeconomic and geological risk indicators; the current version does not include data on extreme temperatures and heat, but this will be expanded and updated in future stages.
Rio without rivers
The map of vulnerability to extreme rainfall developed by Ambiental Media indicates that one of the areas most subject to flooding in the city of Rio de Janeiro is the so-called Jacarepaguá Lagoon Complex, formed by the lagoons of Jacarepaguá, Tijuca and Marapendi and situated between two massifs, Tijuca and Pedra Branca, in the city’s West Zone. Not coincidentally, this is the region that has grown the most in Rio over the last 50 years, becoming the most populous subdistrict of the city, with 653,492 inhabitants.
If there were no city, the rainwater that didn’t infiltrate into the ground would run down the hills, be absorbed by the lagoons and their adjacent mangroves, and then flow out to the sea through rivers and canals. What happens, however, is that this water is met with pavements and the silted-up beds of the lagoons, as well as various channeled rivers. With the ground effectively waterproofed, the water has no way of infiltrating and ends up flooding everything in its path, especially streets and houses.
“When you channelize a river and occupy its banks, especially the floodplains, with urbanization and soil sealing, the river loses these spaces of freedom,” says Adão Cândido, a researcher at the Geography Department at the Federal University of Rio de Janeiro (UFRJ), who has studied the urbanization process in Jacarepaguá. “With its banks sealed, the water can’t infiltrate the soil, resulting in overflow and flooding in the surrounding areas.”
In the case of the Jacarepaguá lowlands, there has been continuous and systematic draining, canalization and landfilling of the main bodies of water and restinga areas (a coastal forest ecosystem) to make room for the real estate expansion that gave rise to upscale neighborhoods like Barra da Tijuca and Recreio dos Bandeirantes. These neighborhoods, it should be noted, were built by a mass of workers who ended up occupying the surroundings of these areas, squeezed in between the hills and the middle- and upper-class buildings.
One place that emerged from this process is Rio das Pedras, currently the second-largest favela (slum) in Rio de Janeiro in terms of number of homes, located in the region of Jacarepaguá. Data from the 2022 census lists 55,653 residents in the favela, but local organizations estimate 130,000 inhabitants.
As is common in Rio’s favelas, disorderly growth over the years has resulted in poor infrastructure and social challenges. In the lower part of Rio das Pedras, 5,392 homes (16%) are in areas that are highly vulnerable to flooding, and 2,206 are extremely vulnerable. In the upper region, on the slopes of Morro do Pinheiro, 273 houses are in areas that are highly vulnerable to landslides.
Elizabeth Bezerra, an environmentalist and 32-year resident of the Vargens region, an outlying area in the Jacarepaguá lowlands, likes to call this “climate gentrification.” “The state pushes residents out of their homes without providing them with any conditions to start over. And where are they going to start over? The law says that if you’re going to remove a community, it needs to be allocated close to its historic site, where there’s a school, a hospital, a doctor, all this social stuff. But that’s not what happens. Where are they going to go if everything is being handed over to unchecked real estate speculation?”
Elizabeth’s account reveals that this strategy of pushing poorer communities into increasingly peripheral areas is a continuous process, taking place today as wealthier neighborhoods expand. The point is that in the Jacarepaguá lowlands, squeezed between two mountain massifs, the less privileged population has nowhere to go but up the hills. Add to that the fact that the ground is incapable of absorbing the water that runs off the hills, and the stage is set for disaster.
And the disaster involves more than a house with water rising up to the walls. In addition to the obvious and incalculable material losses caused by a flood or landslide, there are less noticeable impacts, such as on the water supply and public health. While there is a lack of potable water in these situations, there is plenty of contaminated water, which favors the spread of gastrointestinal, respiratory, dermatological and infectious diseases. Of course, everything gets worse depending on sanitary conditions, especially considering that many communities have no access to basic sanitation.
When adding up all the people affected in one way or another by climate tragedies — floods, cyclones, landslides, torrential downpours, cold fronts, storms — it’s no small number: in the entire state of Rio de Janeiro, around 3 million people suffered some kind of impact between 2020 and 2023, according to Casa Fluminense, an NGO that promotes environmental justice. Included among them are 140 deaths, 1,942 sick people, 8,813 homeless people, 145,077 displaced people, and 229 missing people. In terms of material losses, 94,919 housing units were damaged and another 887 were destroyed, totaling an estimated loss of 1.1 billion reais (about $194 million).
Sirens saving lives
In order to prevent or at least minimize the risk of landslides caused by extreme rainfall in Rio de Janeiro, in 2011 the city government implemented a program known as Sirenes Cariocas, a system of alert sirens that sound whenever rainfall levels indicate the need for preventive evacuation. The program came about in response to the rains of 2010, which left 230 people dead in the state and 35 in the city.
At the time, 168 sirens were installed in around 100 communities vulnerable to landslides. Of these, 164 are still in operation. In other words, not only have four sirens stopped working, but no additional sirens have been installed since; the last installation was back to 2012.
Most of these sirens are located in the city’s North and South Zones, all around the Tijuca massif. The houses built on the slopes of the Gericinó-Mendanha and Pedra Branca mountains, in the city’s West Zone, have so far not been covered by geological-geotechnical studies, fundamental for identifying the areas subject to impacts in the event of extreme rainfall.
A report drawn up by the Municipal Court of Auditors (TCM-RJ) points out that the Sirenes Cariocas program only covers a third of the city’s climate risk areas. Around 400 communities were left out, most of them precisely around the Pedra Branca massif.
It’s worth remembering that the Pedra Branca massif is a stone colossus that is home to the largest urban forest in the world, protected by a state park that covers an area of 125 square kilometers (48 square miles) and surrounded by slopes that cast shadows on 19 of Rio’s neighborhoods, including Curicica, Camorim, Bangu, Campo Grande, Guaratiba, Vargem Grande and Vargem Pequena. The Casa Fluminense map shows that at least 200 homes around Pedra Branca State Park are in areas at high risk of landslides.
“The siren is extremely important,” says Adilson Batista Almeida, one of the leaders of the Camorim quilombo, a traditional Afro-Brazilian community located on the southern flank of Pedra Branca. “The community of Alto Camorim has houses in hillside areas and, although there have been no landslides so far, it is crucial that sirens be installed to prepare the population for emergencies.”
In addition to the sirens, Rio’s residents can find out about the threat of extreme rainfall from the app Alerta Rio, developed by the city government, which shows real-time data on weather conditions and sends warnings when there is a possibility of landslides, with georeferenced information. The system also sends alerts by text message, but people first need to register their postal code by texting 40199.
Another source of information is the Alert Panel from the National Center for Natural Disaster Monitoring and Warning (Cemaden), a research unit linked to the Ministry of Science, Technology and Innovation (MCTI), which also publishes daily bulletins focused on preventing the risk of floods and landslides. This is possible thanks to an extensive network of rain gauges, radars, hydrological stations and, above all, the situation room that Cemaden maintains in São José dos Campos, São Paulo state, where experts monitor Brazil’s municipalities that are most at risk of natural disaster 24 hours a day, seven days a week.
What else can be done
“The sirens are an important tool for minimizing the impact of heavy rains on communities at a high risk of landslides,” says Tharcisio Cotta Fontainha, assistant professor of production engineering at UFRJ and head of the Center for Disaster Engineering Studies and Research. “On the other hand, just having sirens is not enough. It’s important to move ahead with other mechanisms to increase reach to the population.”
Cotta’s statement echoes what was established in 2015 by the United Nations Office for Disaster Risk Reduction during its world conference held in Sendai, Japan: the need to “develop effective global and regional campaigns as instruments for raising awareness and educating society … in order to promote a culture of disaster prevention, resilience and responsible citizenship.”
The Sendai Framework is a call to action for the competent authorities to start including civil society in the fight against the impacts of extreme weather: in other words, to involve residents of at-risk areas in first-aid training and evacuation drills so that they understand what to do in the event of heavy rain.
Still, these are only mitigating measures. Experts are unanimous in saying that it all starts with the way the city itself builds in risk areas. And that responsibility lies with the government.
Geographer Adão Cândido of UFRJ suggests measures such as dredging rivers — removing sediment from the bed so that it can hold more water — efficient garbage collection, and mapping areas of risk. But he warns that flooding will be inevitable in lowland areas, and the actions of the public authorities will be palliative.
“The implementation process in the favelas is expensive and time-consuming,” he says. “In the short term, these improvements are unlikely, but in the long term, actions such as basic sanitation, building popular housing, improving the quality of life and creating river parks and green areas can bring significant benefits.”
Climate urban planner Pedro Henrique de Cristo talks about “redesigning the terrain”: “What we need to do is identify which areas of the city suffer the most from flooding, make an analysis with 4D models and then think about redesigning the terrain in the city — with large-scale flood parks, canals, dikes and turf areas for the ground to soak up the water.”
In practice, it means rethinking the logic of urban space occupying the natural environment, as the Netherlands has been doing for more than 100 years to avoid submergence with dikes, and like China and its sponge cities, where ground-level concrete is replaced with permeable material, interspersed with green areas that can contain excess water, such as flood parks and rain gardens. There are already 16 Chinese cities adapted to become urban sponges.
In the words of Pedro Henrique de Cristo, “We can’t face the climate challenges of the 21st century with the infrastructure and urban planning of the 20th century. We have to carry out major urban reform, recuperate the soil, destroy the concrete and asphalt in order to have flood parks, rain gardens, canals, among other structures that use nature as a constructive element.”
On this subject, Elizabeth Bezerra, the environmentalist from the Vargens region, is somewhat skeptical, pointing out that “the biggest environmental catastrophe in Brazil was in the state of Rio de Janeiro.” She is referring to Jan. 11, 2011, when heavy rains caused landslides in the mountainous region that killed more than 900 people and left another 35,000 homeless. “What has been learned? Nothing. So much so that then came Petrópolis [in 2022], with over 200 deaths. This shows that we, as a state and municipality, haven’t learned from what happens to us.”
And she adds: “Either we build a city thinking together, or we will have to bear the consequences of the seeds that are now being sown all over Rio de Janeiro.”
This story was first published by Ambiental Media on April 2, 2025, supported by the Pulitzer Center and the Serrapilheira Institute.
Banner image of the Vidigal favela in Rio de Janeiro, Brazil. Image by Chensiyuan via Wikimedia Commons (CC BY-SA 4.0).
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