They found that there is a higher relative risk for extreme cold related deaths in northern and southern countries than in western and eastern countries. The researchers also found indication that the effects of heat affected all ages more homogeneously than effects of cold.

Pierre Masselot and Malcolm N. Mistry. Photo: CICERO and LSHTM

London (UK), Paris (France) and Valletta (Malta) had a particularly high risk for the age group of 85 years and older.

“The higher the age, higher is the risk of being negatively affected, both for cold and heat”, says Pierre Masselot, one of the lead researchers in the project.

Heat affects all ages more

Heat related risk was generally lower in the northern region. But in most cities the heat related risk increases in all age groups.

“We found that Paris had the highest heat related relative risk across all ages”, says Masselot.

“However the study included adults aged 20 years and older. So we do not yet know the effects on infants, children and young people” underlines Masselot.  

By providing extensive maps, the study allows to compare vulnerabilities – some groups are more vulnerable to both heat and cold.

Vulnerability factors

What are the factors that increase the likelihood of being negatively affected by either cold or heat stress?

“In particular, the vulnerability to extreme cold and warm temperatures are generally influenced by various factors such as socioeconomic and environmental” says Malcolm N. Mistry, a co-author of the study and a climatologist in the project.

“Identifying the precise factors is often a challenging task adds Mistry. Vulnerability maps produced in this study suggests a link with the size of the city, in the sense that there is a higher relative risk in larger cities” says Mistry.

The study suggests that proximity to water and green areas reduces vulnerability. Also previous studies have found associations between vulnerability to heat and green areas.

The study suggests that proximity to water and green areas reduces vulnerability. Photo: Gunnell E. Sandanger

Socio-economic inequalities are key factors influencing the vulnerability of people.

The researchers also suspect that there are acclimatization issues, both physiological and sociological (e.g. through housing and good practice).

“For instance populations in southern countries avoid much more the sun during hottest hours and houses have shutters” says Masselot. This might partially explain different risks for comparable temperatures.

However, this is very difficult to actually measure and estimate, at least at the city-level. Vulnerabilities also depend on the age structure of the population. In cities with older populations, there is a higher occurrence of excess deaths.

Although there is a higher relative risk for extreme cold related deaths in northern countries, they “showed the lowest risks for heat but also relatively low vulnerability to cold given the much higher exposure to low temperatures” the study shows. This suggests “an adaptive capacity to rigid cold climates, especially when compared with countries in the eastern region”.   

“There are substantial differences in vulnerability between regions, when standardizing for age differences. Countries in Eastern Europe, such as Croatia, Bulgaria and Romania show a higher vulnerability to both heat and cold than countries in Western Europe” says Masselot.

There are substantial differences in vulnerability between regions, when standardizing for age differences. Illustration: Open Maps For Europe and EuroGeographics.

The results of mapping geographical variations in impacts are crucial in the design of national and local health and climate policies to protect more vulnerable populations.

The full paper “Excess mortality attributed to heat and cold: a health impact assessment study in 854 cities in Europe” is available here.