Heat Kills Unequally: Italian Study Maps the Social and Environmental Divide in Summer Mortality

A sweeping nationwide analysis of nearly 1.75 million summer deaths has revealed stark disparities in how heat claims lives across Italy, with the burden falling hardest on the country’s poorest and most environmentally exposed communities. The study, covering all 7,895 Italian municipalities between 2011 and 2023, found that heat was responsible for an estimated 114,812 deaths among people aged 65 and older over the thirteen-year period, accounting for roughly 4.55 percent of all summer mortality in that age group. Behind that national average lies a patchwork of local vulnerability that varies dramatically from one municipality to the next, shaped by factors as tangible as green space coverage and as entrenched as educational attainment and local economic fragility.

The research team assembled daily all-cause mortality records and resident population data from the Italian National Institute of Statistics, restricting their analysis to the summer months of June, July and August and to adults aged 65 years or older, the group known to be most susceptible to heat-related illness and death. Temperature exposure was reconstructed from the ERA5-Land reanalysis product, a dataset produced by the European Centre for Medium-Range Weather Forecasts that blends satellite observations with a land surface model to generate continuous meteorological estimates at a resolution of approximately nine by nine kilometres. Hourly temperatures were averaged across each municipality and condensed into daily mean values, with exposure defined as the mean temperature on the day of death and the three preceding days, a window chosen because the lethal effects of heat are known to be acute.

To disentangle the relationship between temperature and mortality at such a fine spatial scale, the researchers employed a two-stage Bayesian hierarchical model. In the first stage, they fitted municipality-specific non-linear associations between daily mean temperature and death counts using Poisson regression with natural cubic splines, adjusting for day of the week, public holidays, relative humidity, seasonality and long-term trends. From each municipality’s curve they derived a minimum mortality temperature, the local thermal sweet spot at which death risk is lowest, and re-expressed all risks relative to that benchmark. The second stage then examined how a battery of community characteristics, spanning environmental conditions, demographics, healthcare capacity and socioeconomic status, contributed to the spatial disparities in three vulnerability metrics: the relative risk of death at the 90th temperature percentile, the attributable fraction of heat, and the excess death rate per 10,000 population.

The temperature-mortality relationship followed a familiar J-shaped pattern across the country, with risk climbing steeply once temperatures exceeded the 80th percentile of the local distribution. But the annual toll varied enormously from year to year. The median number of heat-attributable deaths ranged from just 1,173 in the mild summer of 2014 to a devastating 17,828 in 2022, when an exceptionally hot season pushed the attributable fraction to 7.10 percent of all summer deaths among older adults. The following year brought only partial relief, with 12,542 attributable deaths and an attributable fraction of 6.00 percent. These figures align closely with recent European analyses of the catastrophic summers of 2022 and 2023, underscoring that the Italian estimates are consistent with the broader continental picture of escalating heat mortality.

The spatial mapping of vulnerability revealed a country divided. Relative mortality risk at the 90th temperature percentile ranged from 1.06 to 1.33 across municipalities, with the steepest risk curves concentrated in Piedmont, Lombardy, Liguria, Tuscany, Marche and Apulia. Yet the researchers observed an important distinction between risk intensity and total burden. Southern municipalities did not consistently show the highest relative risks, but they recorded the largest attributable fractions and excess death rates because high-temperature days occur far more frequently there. In much of the north-east, the attributable fraction of heat stayed between zero and two percent, while many southern municipalities exceeded six percent. More than 80 deaths per 10,000 population were attributed to summer heat in numerous municipalities across the Po Valley, Tuscany, Marche, Apulia and Sicily, compared with a range of zero to 26 per 10,000 in the north-east.

When the team turned to the question of what drives these disparities, the clearest signals emerged from environmental conditions and socioeconomic deprivation. Each standard deviation increase in green space coverage, measured through satellite-derived vegetation indices, was associated with approximately 4.4 fewer heat-related deaths per 10,000 population, a finding consistent with the known capacity of vegetation to cool urban microclimates and deliver co-benefits through reduced air pollution and improved wellbeing. Municipalities with higher average summer temperatures unsurprisingly recorded greater heat mortality, reflecting greater thermal exposure. The proportion of residents aged 85 or older and the prevalence of obesity also showed positive associations, the latter biologically plausible because excess body mass impairs thermoregulation and increases cardiovascular strain.

Perhaps the most striking result concerned the Municipal Fragility Index, a composite measure of territorial and socioeconomic disadvantage. The index displayed a clear dose-response relationship with heat mortality: the higher the fragility level, the greater the heat-related death rate. Compared with the least fragile municipalities, those in the highest fragility category experienced an additional 3.10 heat-related deaths per 10,000 population, even after adjustment for environmental, demographic and health factors. Digging into the twelve individual components of the index, the researchers found that the association was driven primarily by socioeconomic indicators, including low employment rates, low educational attainment, the share of workers in low-productivity sectors and firm density. Transport-related emissions also emerged as a positive predictor of heat vulnerability.

Collectively, the selected community factors explained 44 percent of the spatial variation in excess heat mortality, leaving the remaining majority of variation attributable to unmeasured characteristics. The authors acknowledge several limitations that could shape this residual. Individual-level data on air conditioning access, housing quality and behavioural adaptation were unavailable, though these factors tend to be socially patterned and correlated with the deprivation measures already included. Some covariates, such as obesity and smoking prevalence, were available only at regional level and for a single time point, potentially blurring local variation. Air pollution, a recognised modifier of the heat-mortality relationship, was not examined as a community-level determinant. The coarse resolution of the reanalysis temperature data relative to municipality boundaries may introduce exposure misclassification that underestimates the true toll, and outdoor temperature remains an imperfect proxy for personal exposure, particularly for people who spend most of their time indoors.

The study’s implications reach well beyond Italy’s borders. The methodological framework, built on openly available mortality, population and environmental data, can be transferred to other European settings where comparable records exist. More fundamentally, the findings challenge the assumption that heat adaptation can be delivered through uniform national strategies. The populations most affected by extreme heat are also the least equipped to protect themselves: socially disadvantaged communities face greater exposure, fewer environmental buffers and reduced access to housing, cooling, healthcare and green space. In this way, rising temperatures do not simply add a new health hazard on top of existing inequalities; they actively reinforce them. The researchers argue that climate policy must integrate both environmental and social vulnerability, targeting interventions toward the fragile municipalities where the intersection of heat exposure and deprivation produces the deadliest outcomes.

Subject of Research: Socioeconomic and environmental drivers of spatial disparities in heat-related mortality across Italian municipalities

Article Title: Socioeconomic and geographical disparities in heat-related mortality in Italy: a nationwide small-area study

Article References: Sodano, B., Gascoigne, C., Xi, D., Chen, X., de’ Donato, F., Vineis, P., & Konstantinoudis, G. (2026). Socioeconomic and geographical disparities in heat-related mortality in Italy: a nationwide small-area study. The Lancet Regional Health – Europe, Article 101885. https://doi.org/10.1016/j.lanepe.2026.101885

Image Credits: AI Generated

DOI: 10.1016/j.lanepe.2026.101885

Keywords: heat-related mortality, Italy, small-area study, socioeconomic deprivation, green space, climate change, older adults, Bayesian hierarchical model, municipal fragility, excess deaths, environmental health, vulnerability