With extreme heat now a public health issue, location data can save lives

Eric Macres is senior manager of urban statistics for the WRI Ross Center for Sustainable Cities and attended London Climate Action Week during the June 2026 heatwave. Usama Bilal is associate professor of epidemiology and director of the Urban Health Collaborative at Drexel University.

As thousands gathered in London for one of the world’s biggest climate rallies last week, Western Europe was hit by the worst wave on record. The irony was not lost.

Across Europe, more than a dozen countries have issued emergency heat warnings and Spain has registered the highest death toll. In London, where air conditioning is rare in buildings and on trains and buses, temperatures soared past 36 degrees Celsius (97F) and schools closed early. The mayor announced the city’s first heating system – an important step.

Extreme heat is now a public health problem in many cities around the world, as the effect of urban heat is intensifying dangerous temperatures – and growing exponentially. About 500,000 people die from heatstroke every year. As global temperatures rise, and as a strong El Niño continues, even more people will die and be hospitalized unless cities act quickly.

Eric Macres is senior manager of urban statistics for the WRI Ross Center for Sustainable Cities and attended London Climate Action Week during the June 2026 heatwave. Usama Bilal is associate professor of epidemiology and director of the Urban Health Collaborative at Drexel University.

As thousands gathered in London for one of the world’s biggest climate rallies last week, Western Europe was hit by the worst wave on record. The irony was not lost.

Across Europe, more than a dozen countries have issued emergency heat warnings and Spain has registered the highest death toll. In London, where air conditioning is rare in buildings and on trains and buses, temperatures soared past 36 degrees Celsius (97F) and schools closed early. The mayor announced the city’s first heating system – an important step.

Extreme heat is now a public health problem in many cities around the world, as the effect of urban heat is intensifying dangerous temperatures – and growing exponentially. About 500,000 people die from heatstroke every year. As global temperatures rise, and as a strong El Niño continues, even more people will die and be hospitalized unless cities act quickly.

But many cities still take a more egalitarian approach to dealing with heat, looking only at temperatures and not their spatial effects on people and their health.

People deal with heat differently

How extreme heat affects people’s health can vary greatly from country to city, depending on their location and demographics. Cities can save more lives and prevent more hospitalizations by taking a holistic approach, using data to understand who is most at risk and target solutions to them.

The good news: better data is now available that enables cities to identify who is most at risk. And that data can inform adaptation strategies to save lives. Indeed, the future of cities will depend on their ability to deliver solutions to extreme heat that are designed for vulnerable populations and neighborhoods.

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First, cities should start by measuring the risk of heat to human health in the area. Our work in Brazil and throughout Latin America shows the huge differences in how dangerous temperatures are and how quickly the risks increase at higher temperatures. These differences exist between cities, between population groups and between neighborhoods.

But it’s not as easy as finding the hottest spots. In temperate Porto Alegre, southern Brazil, a person’s risk of death increases by 25% at temperatures of 27 degrees Celsius (81F). In the tropics of Teresina, northern Brazil, which is hot all year round, the same temperature does not pose a risk of death. At 32 degrees Celsius (90F), a person’s risk of death increases by a whopping 10%.

This difference exists even in cities where the climate is the same. The elderly, the very young, low-income communities and those without air conditioning and shaded green spaces are more likely to get sick, hospitalized, or die from the heat. Areas with more trees and green areas generally have lower temperatures, and therefore lower thermal impacts.

Target temperature warnings

Second, cities can use this data to develop early warning systems and outreach campaigns that provide people with more targeted heat warnings. Research in the UK has found that older people, despite being among the most vulnerable, were often unable to heed warnings during the 2022 heatwave. Well-designed heat warning systems and city responses strengthen people’s trust in health services. They can change people’s behavior and better prepare municipal services, helping to reduce morbidity, hospital visits and deaths.

Rio de Janeiro is adopting a heat warning system in 2024 with five warning levels based on the health effects of past heat waves and predictions of when temperatures and humidity will reach those dangerous levels again. Alert levels activate services such as cooling facilities, additional public drinking water, and changes in outdoor events. When the heater struck during Carnival in 2025, the city was able to use resources to protect and warn people while still allowing the events to continue.

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Finally, cities should use local temperature data to target cooling solutions where they can help people the most. Solutions such as tree cover, shade structures and cool roofs reduce the temperature and can provide targeted assistance to the most vulnerable people, such as outdoor workers and those who walk, cycle or use public transport.

In Florianópolis, Brazil, we helped the local government use heat impact modeling to design a green corridor and urban forest project that will reduce pedestrian heat stress by up to 7 degrees C. In Hermosillo, Mexico, our researchers worked with the city and found that certain neighborhoods can feel up to 14 degrees C hotter than the shaded city center. A park is now being built to bring shade and better heat to one of the city’s most vulnerable areas.

Linking health and climate planning

The push to tackle extreme heat in cities is growing, from national and local governments. At last year’s UN climate conference in Brazil, the Belém Health Action Plan saw 30 national health services commit to developing climate-resilient health plans based on local data and evidence-based policies.

And more than 160 local governments have joined the Beat the Heat initiative, committing to develop urban heat applications and deliver passive cooling projects to reduce health risks.

But there is still disunity among health, urban and climate officials. Only 23 percent of the member countries of the World Meteorological Organization integrate weather information into health monitoring systems. Models of the health impact of heat, although becoming easier to measure, have not been developed for all cities. Some cities still need to collect location data for specific areas and neighborhoods – and many need support.

National and local governments will need to work together in this designed approach. It will require integrating local heat and health data into public health programs, urban planning, infrastructure, and disaster preparedness.

We have the data to know who will be most affected by extreme heat if – and the solutions to keep people alive and out of hospital. It is time for governments to use them.