Extreme heat is the new normal.
2024 was the hottest year on record, and 2025 is on track to be Earth’s second-warmest year. Brazil and Argentina experienced soaring temperatures in February, which closed schools and saw Rio de Janeiro’s hottest day in at least a decade. Meanwhile, millions of people were under extreme heat warnings during Texas‘ May heat wave.
The constant headlines of record-breaking temperatures may feel distant, but intense, prolonged heat can upend city operations, devastate infrastructure and reduce quality of life for residents. More importantly, it is the deadliest weather event.
As cities worldwide observe Global Heat Action Day on June 2, and the northern hemisphere gears up for another hot summer, data is key to help cities prepare for and respond to extreme heat.
Here are five data tools and strategies from Bloomberg Philanthropies What Works Cities Certified cities:
- Conduct a heat vulnerability assessment. Cities need to understand not just where it’s hot, but where heat is most dangerous: Some groups of the population are more at-risk of the effects of extreme heat. Heat vulnerability assessments combine demographic, meteorologic, socioeconomic and health data to identify the neighborhoods and communities most at risk of extreme heat. They are compasses for heat response strategies. San Diego, California, made an interactive report that shared background for residents and next steps.
- Turn tree canopy data into action. Planting trees isn’t just about beautification — it reduces carbon emissions, cools neighborhoods and is a visible win for residents. Tree canopy data shows cities where planting efforts can have the most impact; urban trees and nature can cool cities by up to 14°F or 8°C. For instance, in Raleigh, North Carolina, tree canopy data showed that there was a street tree every 40 feet in newer parts of the city compared with one street every 1,000 feet in certain lower-income neighborhoods. In response, the City planted trees where the shade would help reduce urban heat islands the most. Medellín, Colombia’s award-winning Green Corridors program connects newly-planted roads, parks and neighborhoods to reduce urban heat islands, resulting in a 2°C temperature reduction across the city.
- Map heat relief spots. Create a centralized directory where residents can see their closest cooling centers, such as public libraries, recreation centers, public pools, emergency shelters and hydration stations. Washington DC, Las Condes, Chile, and Calgary, Canada, have heat relief maps, while Philadelphia includes cooling spots as part of its heat vulnerability index.
- Empower residents to be a part of the solution. Community engagement can take many forms. The winners of a Norfolk, Virginia, “Datathon” developed a model for the City to better understand the demographics of extreme heat risk. Hamilton, Canada‘s CityLab is a university partnership that has developed more than 230 solutions to pressing community challenges, including one project that assessed the risk and impacts of extreme heat on city facilities. A university group mapped at-risk facilities and made recommendations for energy efficiency and cooling strategies. In 2024, Denver, Colorado, held Heat Summits with community groups, businesses, first responders and more to identify gaps and opportunities in Denver’s heat response strategies.
- Be proactive about the ripple effects of a hotter world. Keeping residents safe during extreme heat is critical, but successful heat strategies recognize that the effects of a warmer world aren’t just heat waves. For instance, rising temperatures are correlated with rising cases of mosquito-borne dengue. In response, Vicente López, Argentina, developed an AI-powered device that detects dengue-carrying mosquitoes species with 90% accuracy and reduces city response times from ten days to real time. Effective water management will also be important. Boise, Idaho, held over 50 community meetings to gain support for a bond to fund a new recycled water facility that will allow Boise to recycle six million gallons of water every day.
