Published online 17 May 2010 | Nature | doi:10.1038/news.2010.238

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Mediterranean most at risk from European heatwaves

Increased heat and humidity predicted to have biggest health impact in valleys and coastal cities.

Rome is one of the cities where the health effects of climate change will be most severe, researchers predict.H. Gjerpen/iStockphoto

A projected increase in heatwaves in Europe would hit low-lying river basins and coastal cities across the Mediterranean the hardest, say researchers.

Erich Fischer and Christoph Schär of the Swiss Federal Institute of Technology in Zurich used global and regional climate models to predict changes in the frequency and duration of summer hot spells in Europe during the twenty-first century. They used a middle-of-the-road scenario for climate change and economic growth to learn about the probable impact on human health.

Different model runs gave wide variation in the severity of heatwaves, but remarkably consistent predictions of where human health would be most affected. The results are reported in this week's Nature Geoscience1.

Heat and high humidity can cause cramps, exhaustion, heat stroke and, in extreme cases, death. The elderly and infants are most vulnerable to its effects. The record-breaking heatwave in 2003 caused 70,000 excess deaths in Europe, and damage to agriculture and forests worth more than €13.1 billion (US$16 billion).

High temperatures are less damaging to health when the air is dry. But the models project that people in valleys and cities by the Mediterranean Sea will experience both heat and high humidity.

Hotting up

"Low-lying humid plains, such as around the River Po in northern Italy, and coastal cities such as Athens, Rome and Marseilles, are likely to be more severely affected by dangerous heat conditions than higher and drier inland regions," says Fischer.

Click for a larger version.Erich Fischer

By 2100, the study finds, some parts of the area could experience 40 extremely warm days each year, compared with an average of just two between 1961 and 1990. Night-time temperatures above 20 °C and high relative humidity are likely to worsen the impact on health of extended heatwaves, the study warns.

The scientists did not consider the effect of air pollution and urban 'heat islands' that make cities still warmer. Both factors could increase the health consequences of heatwaves. A study released earlier this month found that in hot climates the effect on temperature of urban heat islands is equivalent to doubling the concentration of carbon dioxide in the atmosphere2.

Health impact

In 2008 the World Health Organization (WHO) analysed the health effects of heatwaves for 15 European cities. It estimated that, over a given threshold, every 1 °C increase in 'apparent' temperature — a measure of the combined effect of heat and humidity — leads to a 3% increase in mortality in Mediterranean cities3.

In the United States, authorities issue a heat advisory when the apparent temperature is likely to exceed 41 °C.

"We know that human health is sensitive to climate change," says Bettina Menne, a global change and health expert at the WHO regional office for Europe in Rome, Italy. "The high-resolution modelling work for the new study is an interesting bit of extra information that could prove very beneficial for our own epidemiological research into heatwave mortality," says Menne, who oversees EuroHEAT, a WHO-led programme aimed at improving the public-health response to weather extremes.

Developing efficient health actions and warning capabilities for heat extremes will be vital, says Fischer. "No question, you can adapt to heat," he says. "But you do need to tell people how to behave, and how not, when it gets really hot." 

  • References

    1. Fischer, E. M. & Schär, C. Nature Geosci. advance online publication doi:10.1038/NGEO866 (2010).
    2. McCarthy, M. P., Best, M. J. & Betts, R. A. Geophys. Res. Lett. 37, L09705 doi:10.1029/2010GL042845 (2010). | Article
    3. Baccini, M. et al. Epidemiology 19, 711-719 (2008). | Article
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