Urban Heat Islands and Inequalities: Evidence from French Cities

During heat waves, urban heat islands (UHIs) affect city neighbourhoods in heterogeneous ways due to differences in urban form, building quality, vegetation and human activity. Some populations are particularly vulnerable, such as the elderly, young children and low-income households, who have fewer options for dealing with UHI. In this article, for the first time we measure household exposure to UHI as a function of income in the main French cities. We construct and compare finely localised data on temperature, vegetation, residential building density, height and period of construction, and socio‑economic characteristics of households in nine of France's largest cities. We find that the relationship between exposure to UHI and income depends on pre-existing spatial sorting. In cities such as Paris, the French capital, where affluent and low-income households reside close to the city centre, exposure to UHI as a function of income follows a U-shaped curve. In contrast, in cities where affluent households live in wealthy suburbs, such as Lyon, France's second largest city, exposure to UHI decreases with income. We also find that vulnerable households, defined by both age and income criteria, are slightly more exposed but much less able to renovate their homes or leave the city during heatwaves.