Socioeconomic variables pinpointed in urban-heat mortality risk

January 8, 2021

A study of Italian data shows some surprises when it comes to who suffers the most from extreme heat. (AP Photo/Luca Bruno)

Unmarried people who live alone, women with little education and, more surprisingly, men at opposite ends of the education spectrum were at higher risk of death due to increasingly severe high temperatures in northern Italy, according to the first comprehensive assessment of social inequalities in the relationship between urban heat and health outcomes.

The analysis of close to four decades’ worth of Italian data, published in November in Environmental Health, could help inform policymaking in European and particularly Mediterranean areas where already deadly summer temperature spikes will likely become more extreme as the planet continues to warm. Extreme high temperatures are the largest cause of weather-related mortality among all natural disasters, and people in urban settings are at particular risk of mortality because of cities’ compactness, dependency on infrastructural systems and higher concentration of people and economic activities.

To arrive at their conclusions, researchers leveraged the population-based database Turin Longitudinal Study to track daily summer temperatures alongside daily mortality rates between May 15 and Sept. 15 each year from 1982 to 2018. With more precision than is typical, they documented a wider variety of characteristics among the deceased — not just the well-established demographic factors of age and gender but also socioeconomic variables including educational level, marital status and household occupancy. 

The factors were determined through a previous literature review by Marta Ellena, lead author of the latest study and a researcher at the CMCC Foundation, or Fondazione Centro Euro-Mediterraneo sui Cambiamenti Climatici (Euro-Mediterranean Center on Climate Change). 

The study, which was coordinated by the Caserta, Italy-based foundation and the Barcelona Institute for Global Health, is also notable for its focus on Italy. No other Mediterranean country has more significant heat-related effects on summer mortality, yet few projects have analyzed the link between heat and health in the area.

For both genders, the study found that mortality risk rose with age, and people living alone were at higher risk than married ones. Men specifically were also found to be at greater risk when living alone as compared to people sharing a home with others. 

While the age finding was “quite expected,” Ellena said, the dwelling findings were largely without precedent. The extensiveness of the dataset is what allowed the researchers to examine both marital status and occupancy levels, something that had not yet been done in Italy and had only been done once before in Europe, in France.

As expected, the researchers also found that women were “systemically” at higher risk than men under stressful heat conditions, possibly due to physiological reasons or the likelihood of women to live longer and live alone in their elderly years. 

When it comes to education, the researchers found an interesting and novel gender-based distinction: While women with the least educational attainment were at higher risk, as is often assumed, men faced the most risk when at either the highest or lowest education levels. That could reflect the fact that men die younger, particularly if they’re less educated. 

The surprising finding with regard to men might be explained in part by the social stratification that resulted from the migration of residents from southern regions into Turin and other northern cities in recent decades. While minimally educated men were subject to premature mortality, the most-educated men simultaneously found fewer career opportunities because of discrimination from Turin natives.

“Ten years ago the situation in terms of integration was not so open-minded as now, so this could also play a role,” Ellena said.

Turin, the capital of the Piedmont region of northwest Italy, is the country’s fourth-largest urban area. Known for dry summers and mild, wet winters, Turin sits 800 feet above sea level and is also home to many unique microclimates because of its proximity to the Alps.

Ellena has now been examining smaller sections of the longitudinal data to zero in on how different adaptation methods such as new social services could make populations more resilient. She hopes to publish this month.

She and her colleagues also plan to run the same model used for this study to examine different districts, neighborhoods and statistical areas within Turin to map risk distribution and inform public policy.

Understanding heat risks at such a granular level could help government officials implement safety measures such as an early warning system. Following the 2003 European heat waves that resulted in at least 30,000 deaths, Italy and other countries used such a system to distribute bulletins when extreme heat was expected, so the most vulnerable could seek protection. Italy’s experiment was short-lived, despite its effectiveness.

The researchers are also working with the Copernicus data platform, the European Union’s satellite Earth observation program, to develop a new climate simulation designed for urban areas to evaluate how risk will evolve in Turin as climate change leads to more extreme conditions such as longer and more frequent heat waves.

“To be honest, we don’t expect that the risk will decrease,” said Paola Mercogliano, a co-author on the paper and director of the CMCC Foundation’s regional models and geo-hydrological impacts division.

The study "Social inequalities in heat-attributable mortality in the city of Turin, northwest of Italy: a time series analysis from 1982 to 2018," published Nov. 16 in Environmental Health, was authored by Marta Ellena, Università Ca’Foscari Venezia and Fondazione Centro Euro-Mediterraneo sui Cambiamenti Climatici; Joan Ballester, Barcelona Institute for Global Health; Paola Mercogliano, Fondazione Centro Euro-Mediterraneo sui Cambiamenti Climatici; Elisa Ferracin, Regional Epidemiology Unit, ASL TO3 Piedmont Region; Giuliana Barbato, Fondazione Centro Euro-Mediterraneo sui Cambiamenti Climatici; Giuseppe Costa, Regional Epidemiology Unit, ASL TO3 Piedmont Region; and Vijendra Ingole, Barcelona Institute for Global Health.

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