Madrid. The risk of fatal heat waves will become more frequent and the excess mortality associated with them will increase. Europe will be particularly affected, reveals a new study from ETH Zurich.
Waves like the ones the world is experiencing today are particularly fatal for the elderly, the sick and the poor. The one that Europe suffered in 2003 and caused temperatures to reach 47.5 degrees Celsius, was one of the worst natural disasters in recent decades and claimed between 45,000 and 70,000 victims in a few weeks. Forests burned, crops withered, and emergency rooms were packed to capacity.
Globally, the costs amounted to about $13 billion. However, the public remains less aware of the weather-related risks of heat waves. This is a problem, says the new study published in the journal Nature Communications. Episodes like the one in 2003 could become the new norm for years to come.
Researchers from ETH Zurich’s Institute for Environmental Decisions collaborated with an international group of epidemiologists on the study. Since 2013, they have systematically collected data on daily heat-related excess mortality in 748 cities and communities in 47 European countries, Southeast Asia, Latin America, the United States, and Canada.
With this data set, they calculated the relationship between the average daily temperature and mortality in those places and were able to establish the ideal temperature for each one where the excess mortality is the lowest. In Bangkok, for example, this value is 30 degrees Celsius, in Sao Paulo 23, in Paris 21 and in Zurich 18 degrees Celsius.
Every tenth of a degree above this ideal value increases excess mortality. “Not all heat is the same,” explains Samuel Lüthi, lead author of the study and Professor David Bresch. “The same temperature has a completely different impact on heat-related excess mortality in the populations of Athens and Zurich.”
This depends not only on temperature, but also on physiology (acclimatization), behavior (long naps in the middle of the day), urban planning (green spaces versus concrete), the demographic structure of the population and the local health system. .
Lüthi has calculated the impact of more than 7,000 years of physically possible weather events on heat-related mortality.
The results show that the risk of heat waves with high excess mortality has already increased markedly in the last 20 years. “Excess mortality from a hot summer like 2003 used to be considered a once-in-a-century extreme event. We now expect it to happen once every 10 to 20 years,” he notes.
zones detected
Heat mortality figures that were considered unlikely in 2000 (once every 500 years), will occur 14 times every 100 years in a 2 degree scenario. Assuming no heat adaptation, the probability of mortality during such extreme waves will increase by a factor of 69.
Regions at particular risk from rising waves include the Gulf and Atlantic coasts of the United States, as well as the Pacific coast of Latin America; The middle east; Southeast Asia, and the Mediterranean. Even in moderate scenarios, a hot summer can cause 10 percent of all deaths in a country to be heat related.
Paris was particularly hard hit in 2003. The figure was 5 to 7 percent, meaning that there alone the wave caused the premature death (by dehydration, heat stroke and heart attack) of around 2,700 people.
“According to our calculations, in the future up to 15 percent of deaths in Paris could be related to heat,” says Lüthi.
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