Rio endures over 33 scorching summer days above 36°C, half the season defined by intense thermal stress

Rio endures over 33 scorching summer days above 36°C, half the season defined by intense thermal stress

Rio de Janeiro has experienced significant thermal stress for more than half of its summer season, as of Friday, January 20, 2025. This condition, characterized by a challenging combination of elevated temperatures and high humidity, has profoundly impacted daily life in the sprawling metropolis. With the season’s onset on December 21, 2024, the city has already grappled with a substantial number of dangerously hot days, prompting official responses and public health advisories.

Specifically, out of 61 days of summer recorded until Thursday, January 19, 2025, an astonishing 33 days registered high heat indices, with temperatures consistently ranging between 36°C and 40°C. These figures, released by the Rio City Hall’s Operations and Resilience Center (COOR), underscore the intensity and persistence of the heatwave.

The severity of these conditions led to the city’s Heat Extreme Protocol being activated multiple times. On Friday, the municipality reverted to Level 1, signaling a slight reprieve, but only after enduring a relentless eight-day stretch at more critical Levels 2 and 3.

Persistent heat patterns challenge the city

The city’s struggle with extreme heat saw seven consecutive days classified under Calor 3, the second-highest alert level, followed by a day at Calor 2. These sustained periods of intense heat and humidity are not isolated incidents but rather reflect a recurring climatic pattern observed in recent summers.

According to meteorologists, the combination of high temperatures and elevated humidity creates a significantly magnified sensation of heat, leading to increased discomfort and health risks for residents. This phenomenon also plays a role in the intensity of summer rainfall.

Dual alerts: heat transitions to heavy rain

While the city navigated the lingering effects of extreme heat, a new alert emerged on Friday evening, shifting the municipality to Stage 2 attention for an entirely different reason: heavy rainfall. This stage, the second level on a five-point scale, signifies a heightened risk of high-impact occurrences across the city.

Forecasters anticipate moderate to strong downpours, potentially accompanied by lightning, through Friday night and into the early hours of Saturday, January 21, 2025. City officials have warned of the possibility of further stage changes, depending on the evolving weather conditions and other contributing factors, keeping emergency services on high alert.

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Mirroring past thermal stress trends

The high temperatures and humidity levels recorded in Rio since December 21, 2024, are indicative of a climatic pattern that mirrors the challenges faced during the previous summer season (December 21, 2023, to March 20, 2024). During that 89-day period, the city experienced 46 days marked by significant thermal stress, necessitating the activation of Calor 2, Calor 3, and even Calor 4, which is the most critical alert level.

Raquel Franco, the chief meteorologist for the Alerta Rio System, emphasized the typical nature of this pattern. “We have had thermal stress on more than half of the season’s days, and this pattern is characteristic of summer in Rio de Janeiro,” Franco explained. “The combination of high temperatures and humidity generates an amplified sensation of heat.”

She further elaborated that these concurrent factors also contribute to the occurrence of strong rains, which are another defining characteristic of the summer season in the region. This interplay between heat and precipitation highlights the complex meteorological dynamics impacting the city.

Health impacts surge amid intense heat

The intense heat gripping Rio has led to a noticeable increase in demand for medical attention across the city’s health units. The Municipal Health Secretariat (SMS) reported that approximately 13,500 individuals sought treatment for heat-related symptoms during the current summer period.

Common ailments included sunstroke, dehydration, respiratory problems, and fluctuations in blood pressure, all exacerbated by the oppressive heat. Public health officials continue to advise residents to take precautions such as staying hydrated, avoiding direct sun exposure during peak hours, and seeking shade to mitigate the health risks associated with the prolonged thermal stress.

The sustained period of elevated temperatures places a significant strain on the public health infrastructure, requiring increased resources and vigilance from medical professionals. The city remains proactive in disseminating information on preventive measures to safeguard its population against the adverse effects of extreme weather.

Rio de Janeiro heat, thermal stress, summer 2025, high temperatures, heatwave health impacts