Extreme heat is increasingly affecting cities, with new data showing that the burden is rising fastest for poorer, densely populated communities.
These areas are often more exposed and less able to cope with soaring temperatures, highlighting deep social and environmental inequalities in urban heat risk.
A global data platform, launched this week, maps urban heat at street level, revealing how temperatures vary across neighbourhoods – and where interventions could reduce risk.
Cool Cities Lab, developed by the World Resources Institute’s Ross Centre for Sustainable Cities, allows planners to identify heat hotspots and test the potential impact of measures such as tree planting, shaded infrastructure and reflective roofing before they are implemented.
Its release comes as governments face mounting pressure, including through UN climate negotiations, to respond to rising temperatures that are affecting public health, infrastructure and economic activity in cities.
“For millions of people in cities, extreme urban heat is no longer a short-term event or seasonal disruption. It’s an existential threat,” the platform said.
At recent UN climate conferences, countries have acknowledged that while efforts to limit global warming continue, adaptation to intensifying heat is unavoidable, particularly in urban areas where exposure is concentrated.
Globally, heat exposure is linked to an estimated 489 000 deaths a year.
Its release comes as cities face rising temperatures and more frequent heatwaves. In the world’s largest capital cities, the number of days exceeding 35°C has risen by 25% since the 1990s.
“If global temperatures rise by 3°C, cities can expect the intensity and duration of heatwaves to double,” the platform warns.
As global climate negotiations continue to emphasise both mitigation and adaptation, the pressure on cities to respond to heat – and to do so with precision – is increasing.
The effects extend beyond mortality, with rising temperatures driving up hospital admissions, reducing labour productivity and placing additional strain on infrastructure.
Within cities, exposure is uneven. “People experience extreme heat very differently depending on their circumstances,” the platform adds, noting that lower-income and densely built communities often face higher temperatures and limited access to cooling.
South African cities, among them Cape Town, Johannesburg and Durban, are included in the dataset.
In Cape Town, areas such as Langa and Joe Slovo are shown to experience higher heat exposure than other parts of the city, reflecting disparities in vegetation cover, density and infrastructure.
The platform combines data on land cover, buildings, vegetation and population density to show how heat varies across short distances. “It maps heat at a scale people actually experience,” the material states, highlighting differences that are not captured in citywide averages.
It also allows users to model interventions before implementation. “Cool Cities Lab lets cities test solutions such as trees, shade and cool roofs to see how much they would lower heat risks in specific places before making investments.”
Urban heat is increasingly being treated as a public health issue. Exposure to high temperatures is linked to heat exhaustion, respiratory strain and cardiovascular stress, particularly among vulnerable groups such as the elderly, outdoor workers and those living in poorly insulated housing.
Economic impacts are also emerging. “Heat slows workers down, damages infrastructure and puts people at greater risk for health crises,” the platform notes. Cities could lose up to 1.7% of gross domestic product due to heat-related effects by 2050.
Despite the risks, many cities lack localised data to guide responses. “Most cities are still making decisions without a clear picture of where heat is worse or which solutions will make the biggest difference,” according to the platform’s background material.
The tool is designed to address the gap by linking interventions to measurable outcomes. In one example, increasing street tree coverage by 20% in a neighbourhood in Campinas, Brazil, could reduce felt temperatures by between 1.7°C and 8°C.
In Hermosillo, Mexico, the data has been used to identify areas with low vegetation and high temperatures, informing plans for a new urban park aimed at providing relief from heat.
The platform also models combined interventions. In Cape Town’s CBD, it shows that expanding tree cover alongside reflective roofing could reduce temperatures and improve conditions at street level.
Cooling measures themselves are established. “During times of extreme heat, shade is vital,” the platform states, noting that shaded areas can feel between 5°C and 11°C cooler than direct sunlight.
What has been less accessible is the ability to quantify the effects at the neighbourhood level. “Cool Cities Lab gives city leaders and planners a clear view into data they can use to make the case for action,” it says.
The platform is built on open-source data and is intended for use by governments, researchers, development finance institutions and civil society organisations.
A new global platform maps urban heat at street level, showing how exposure is rising and falling disproportionately on poorer communities, while giving cities tools to test cooling solutions