Researchers at the Rome Regional Health Authority (Italy) investigated nine European cities (Athens, Greece; Barcelona, Spain; Budapest, Hungary; London, United Kingdom; Milan, Italy; Munich, Germany; Paris, France; Rome, Italy; and Valencia, Spain) and calculated city specific and pooled estimates of mortality by gender, age, and cause of death. Both temperature and humidity levels during the day, as well as high nighttime temperatures, were considered when defining heat waves, a definition based on a period of at least 2 days when Tappmax--a numerical interaction between maximum air temperature and humidity--was among the highest monthly 10%, or when the minimum temperature was among the highest 10%, with Tappmax above the average.

The results showed that heat waves of long duration had the greatest effect on mortality, resulting in a 1.5- to 3-fold higher daily mortality than for shorter heat waves. The elderly, especially women, appeared to be most at risk during heat waves, with excess mortality due to respiratory (not cardiovascular) causes. A significant increase in total daily mortality during heat waves was observed in all cities, with the greatest increase in Milan (+33.6%) and the lowest in Munich (+7.6%). The researchers focused separately on the extreme 2003 heat wave that swept across Europe, when all cities except Athens and Budapest showed an increased mortality of 30%-100% compared with other years; once again, the highest effect was observed for respiratory diseases and among women aged 75-84 years. The study was published early online in the July 15, 2010, issue of Environmental Health.

"The greatest impact on mortality was observed in cities where heat wave episodes are rare events or were characterized by temperatures largely outside the usual meteorological conditions,” concluded lead author Daniela D'Ippoliti, Ph.D., and colleagues of the department of epidemiology. "Considering our results, prevention programs should specifically target the elderly, women, and those suffering from chronic respiratory disorders, thus reducing the impact on mortality.”

Climate change forecasts for Europe in the coming years predict an increase in the frequency and the intensity of heat waves, especially in central, southern, and eastern areas, and as a consequence, heat-related mortality is expected to become a relevant threat even in cities usually not exposed to extreme hot temperatures.

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Rome Regional Health Authority