In a recent study published in The Lancet Planetary Health Journal, researchers comprehensively assessed the mortality impact of non-optimal temperatures in European cities and determined the varying risk due to demographic and vulnerability factors.
Study: Excess mortality attributed to heat and cold: a health impact assessment study in 854 cities in Europe. Image Credit: RuslanHuzau/Shutterstock.com
Although extremely high and low temperatures are established risk factors associated with mortality rates worldwide, climate change and global warming are expected to exacerbate the health burden of non-optimal temperatures.
However, because the vulnerability to extremely high and low temperatures is influenced by various climatic, socioeconomic, and environmental factors, obtaining a robust estimate of the mortality burden of heat and cold has proven difficult.
Close to 40% of the population of Europe is believed to live in cities, and the stress associated with extreme temperatures, especially heat, is more pronounced in urban areas.
Furthermore, the vulnerability to extreme temperatures also varies according to socioeconomic, climatic, and environmental factors significantly different across European cities.
Hitherto, the assessments of the mortality burden of extreme temperatures have been conducted either on local or regional levels or on much larger scales and have failed to capture the varying local vulnerabilities according to demographic, geographical, or environmental factors.
About the study
In the present study, the researchers compiled a comprehensive list of cities in Europe, excluding remote locations overseas with highly variant climates from regions in mainland Europe.
These cities obtained the daily all-cause and non-accidental daily mortality counts and vital statistics comprising demographic structure and crude death rates.
The mean air temperatures two meters above the ground were obtained for all the cities between 1990 and 2019.
Additionally, a set of city-specific variables that could influence the vulnerability patterns across European urban populations were also collected. These variables covered the cities' infrastructural, socioeconomic, topographical, and environmental characteristics.
Remote sensing satellite data was used to obtain information on variables such as normalized difference vegetation index, fine particulate matter, and the concentration of nitrogen dioxide. Land cover characteristics such as tree cover, water, grasslands, wetness, etc., were also included in the analysis.
A modeling framework was used to assess the mortality impact of heat and cold specific to age and the city. The vulnerability patterns based on demographic and city-specific factors were used to derive excess mortality rates associated with heat and cold and minimum mortality temperatures.
The results reported that the annual excess mortality associated with heat and cold across 854 European cities was 20,173 and 203,620, respectively, corresponding to 13 and 129 deaths per 100,000 person-years.
The vulnerability to extreme temperatures was seen to increase with age, although the vulnerability to cold was seen to increase more steeply with age than the vulnerability to heat. Over 60% of the mortality burden consisted of individuals above the age of 85 years.
The vulnerability across regions was also found to differ substantially. Eastern European regions in countries such as Bulgaria, Croatia, and Romania were seen to be more vulnerable to the impact of heat and cold than Western European countries.
Apart from large cities such as Paris and London, western European regions were seen to have lower excess mortality than the eastern, northern, and southern regions of Europe.
While the risk associated with high temperatures was low for northern European countries, the low vulnerability to cold despite the extremely low temperatures in the region indicated that the individuals in these regions had adapted to the rigidly cold climate.
The authors believe that local climatic differences, health care access, urban heat island effects, and the tree and water cover over land could explain the differing vulnerabilities to heat and cold across European cities.
To summarize, the study investigated the excess mortality related to heat and cold across 854 European cities spanning all geographic regions of the continent.
Overall, the results suggested that the vulnerability to heat and cold increased across the north-to-south and west-to-east gradient, with eastern European countries experiencing high vulnerability to heat and cold.
Factors such as land cover, access to health care, and local and regional differences in climatic factors are thought to explain the varying vulnerability of European cities to heat and cold.