A new study published in Nature on July 21, 2025, has uncovered a dangerous intersection of extreme heat and worsening air quality in Kigali, Rwanda offering a stark warning for fast-growing cities across sub-Saharan Africa.
The research, conducted between May 2021 and December 2024, shows how Kigali’s rapid urbanisation coupled with vehicle emissions, biomass burning, and stagnant air conditions has created a perfect storm of heat and pollution. As one of Africa’s fastest-growing capitals, Kigali now faces increasingly frequent heatwaves and high levels of harmful pollutants like PM2.5, nitrogen dioxide (NO₂), and ozone (O₃).
Drawing data from 12 air quality monitoring stations operated by the Human Environment, Location, Transport and Health Research Lab and Rwanda’s Environmental Management Authority, the study tracked pollution patterns alongside temperature spikes. Meteorological data was also gathered from the Rwanda Meteorological Agency.
Researchers defined heatwaves as three or more consecutive days with maximum temperatures at least 5°C above the city’s average. Between 2021 and 2024, Kigali’s average maximum temperature was 25.28°C, with six heatwaves recorded peak temperatures reaching up to 33.5°C.
The study found clear seasonal and daily trends: NO₂ levels were higher during the dry season, while PM2.5 and ozone concentrations peaked during the wet season. Pollution levels surged during morning (6 am–9 am) and evening (5 pm–11 pm) rush hours. Ozone, driven by photochemical activity, peaked in the afternoon (1 pm–4 pm). PM2.5 levels frequently exceeded WHO guidelines—sometimes rising over eight times the recommended limit.
The most intense heatwaves, in January 2022 and June 2023, lasted five days and were linked to significant spikes in PM2.5 and ozone, although NO₂ remained relatively stable. However, the highest temperature event in March 2022 did not coincide with the worst pollution, showing that heat and pollution don’t always align but when they do, the health risks amplify.
The paper highlights the urgent need for integrated urban planning that considers both rising heat and deteriorating air quality. The dual threat poses serious health risks particularly for children, the elderly, and those with pre-existing respiratory or heart conditions.
“Sub-Saharan Africa’s urban future depends on building climate-resilient, health-conscious cities,” the authors warned. They called for early-warning systems, targeted public health advisories, and sustainable transport policies to reduce emissions.
With urbanisation accelerating and climate extremes becoming the new norm, cities like Kigali stand at a crossroads one that demands immediate, science-based policy action