Study Reveals Overlooked Inequality in Urban Heat Risk
06 Nov 2026
People differ in how susceptible they are to heat and how well they can adapt to it. A study of 1,029 cities worldwide found that overlooking these differences in social vulnerability underestimates inequality in urban heat risk.
The study was conducted by a team led by Prof. MENG Qingyan from the Aerospace Information Research Institute of the Chinese Academy of Sciences (AIRCAS), together with collaborators. It was published in Communications Earth & Environment.
From 2000 to 2019, average urban heat risk in the Global South was 203.0% higher than in the Global North when differences in social vulnerability across locations were taken into account. When all populations were assumed to be equally vulnerable, the estimated gap was 65.0 percentage points smaller.
Limited data have led many global assessments to estimate heat risk from how often heatwaves occur and how many people are exposed. To also capture differences in susceptibility and the capacity to adapt, the researchers developed a multidimensional social vulnerability index.
The index combined demographic, economic, and environmental indicators: the proportions of children and older adults, GDP per capita, air-conditioning penetration, urban vegetation, and fine particulate matter (PM₂.₅) concentrations.
The team then compared two measures: exposure risk, based on heatwave frequency and the exposed population, and comprehensive heat risk, which also accounted for differences in social vulnerability across locations.
Urban heat risk increased in more than 84.4% of the cities studied. The increases were statistically significant in 38.8% of cities, home to nearly 398 million urban residents. The main hotspots were concentrated in major clusters of cities across South Asia, Southeast Asia, and Central and West Africa.
The larger the income gap between regions, the more exposure risk alone understated inequality in urban heat risk. The researchers quantified this underestimation by comparing the relative disparities calculated with and without differences in social vulnerability across locations.
Using high-income countries as the reference group, exposure risk alone understated the heat risk disparity by 46.8 percentage points for upper-middle-income countries and by 216.8 percentage points for low-income countries.
Differences in social vulnerability also affected how unevenly heat risk was distributed among cities within each region. The Gini index, a measure of this inequality, was 0.47 for long-term average heat risk in the Global North and 0.41 in the Global South. This indicated a more uneven distribution in the Global North. Using exposure risk alone underestimated the index by 14.5% in the Global North and 4.6% in the Global South.
These findings can help planners identify which cities should be prioritized for heat adaptation. Combining heatwave and population data with information on susceptibility to heat and access to cooling can change where the greatest needs for heat protection are identified.
Global long-term averages and trends in urban heat risk. (Image by AIRCAS)
Interregional inequality in urban heat risk. (Image by AIRCAS)
Research News
Study Reveals Overlooked Inequality in Urban Heat Risk
People differ in how susceptible they are to heat and how well they can adapt to it. A study of 1,029 cities worldwide found that overlooking these differences in social vulnerability underestimates inequality in urban heat risk.
The study was conducted by a team led by Prof. MENG Qingyan from the Aerospace Information Research Institute of the Chinese Academy of Sciences (AIRCAS), together with collaborators. It was published in Communications Earth & Environment.
From 2000 to 2019, average urban heat risk in the Global South was 203.0% higher than in the Global North when differences in social vulnerability across locations were taken into account. When all populations were assumed to be equally vulnerable, the estimated gap was 65.0 percentage points smaller.
Limited data have led many global assessments to estimate heat risk from how often heatwaves occur and how many people are exposed. To also capture differences in susceptibility and the capacity to adapt, the researchers developed a multidimensional social vulnerability index.
The index combined demographic, economic, and environmental indicators: the proportions of children and older adults, GDP per capita, air-conditioning penetration, urban vegetation, and fine particulate matter (PM₂.₅) concentrations.
The team then compared two measures: exposure risk, based on heatwave frequency and the exposed population, and comprehensive heat risk, which also accounted for differences in social vulnerability across locations.
Urban heat risk increased in more than 84.4% of the cities studied. The increases were statistically significant in 38.8% of cities, home to nearly 398 million urban residents. The main hotspots were concentrated in major clusters of cities across South Asia, Southeast Asia, and Central and West Africa.
The larger the income gap between regions, the more exposure risk alone understated inequality in urban heat risk. The researchers quantified this underestimation by comparing the relative disparities calculated with and without differences in social vulnerability across locations.
Using high-income countries as the reference group, exposure risk alone understated the heat risk disparity by 46.8 percentage points for upper-middle-income countries and by 216.8 percentage points for low-income countries.
Differences in social vulnerability also affected how unevenly heat risk was distributed among cities within each region. The Gini index, a measure of this inequality, was 0.47 for long-term average heat risk in the Global North and 0.41 in the Global South. This indicated a more uneven distribution in the Global North. Using exposure risk alone underestimated the index by 14.5% in the Global North and 4.6% in the Global South.
These findings can help planners identify which cities should be prioritized for heat adaptation. Combining heatwave and population data with information on susceptibility to heat and access to cooling can change where the greatest needs for heat protection are identified.
Global long-term averages and trends in urban heat risk. (Image by AIRCAS)
Interregional inequality in urban heat risk. (Image by AIRCAS)