Urban Heat Islands and Inequalities: Evidence from French Cities

During heatwaves, urban heat islands (UHI) affect cities neighborhoods heterogeneously due to differences in urban form, building quality, vegetation, and human activity. Some populations are particularly vulnerable, such as older adults and young children or low-income households, who have fewer options facing UHI. In this paper, for the first time, we measure UHI exposure among households depending on their income in the major French cities. We build and match finely localized data on temperature, vegetation, residential building density, height and period of construction, and households socioeconomic characteristics across nine of the largest French cities. We find that the relationship between UHI exposure and income depends on their pre-existing spatial sorting. In cities like Paris, the French capital, where both affluent and low-income households reside close to the city center, UHI exposure by income follows a U-shaped curve. In contrast, in cities where affluent households live in rich suburbs, like Lyon, France's second largest city, UHI exposure decreases with income. We also find that vulnerable households, defined by both age and income criteria, are slightly more exposed but far less able to renovate their dwellings or leave cities during heatwaves.