Sweltering nights are quietly raising the risk of death, according to a major new study that links night-time heat to a 3% increase in mortality.
The research, published in Environmental International, shows that hot nights have a dangerous impact independent of daytime heat, calling for tailored public health measures.
The work draws on data from over 14 million deaths across 178 cities in 44 countries between 1990 and 2018.
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More than 40 institutions took part, including Spain’s National Research Council (CSIC) via its centres in Galicia, Catalonia and Andalucia, as well as the Universitat de Valencia.
Researchers used heat indices and advanced statistical models, focusing on Spanish provincial capitals where sufficient records were available.
The findings reveal that hot nights increase heat-related deaths in almost every climate studied, with the exception of northern Europe, where the effect was less marked.
‘Heat during the night prevents the body from recovering after daytime stress, disrupts sleep, and can worsen cardiovascular, respiratory and neurological conditions,’ said Dominic Roye, a researcher at the Biological Mission of Galicia.
He added that cities with strong urban heat island effects face an even harsher impact.
Roye pointed to Madrid, Valencia, Barcelona and Sevilla as particularly vulnerable due to their frequent tropical and equatorial nights.
Many other cities in Andalucia also face such circumstances, including Cordoba and Jaen.
Older adults, people with chronic illnesses, and residents in poorly ventilated homes or without air conditioning are among the most at risk.
The study urges authorities to factor night-time heat into early-warning systems, and calls for more urban cooling strategies.
Proposals include climate refuges, expanded green spaces, and stricter requirements for thermal comfort in homes, hospitals and care facilities.
‘Tropical nights have increased sharply in recent years due to climate change. This summer was exceptional, and the situation is worsening, raising the risk for the most vulnerable,’ warned Aurelio Tobias, of the CSIC’s Institute of Environmental Assessment and Water Research.
Scientists stress the need for further research into how daytime and night-time heat interact in different urban climates. They also highlight unanswered questions over whether short bursts of extreme heat are deadlier than prolonged periods of elevated night-time temperatures.
The study adds fresh weight to growing evidence that climate change is reshaping the daily rhythm of risk – not only through blistering daytime highs, but through the relentless grip of heat that refuses to fade after sunset.
Read more Andalucia news at the Spanish Eye.
