Heat-related deaths are widespread across Washington state, and they occur even in regions that typically have milder climates, according to a new University of Washington study published in the journal Atmosphere.
This is the most extensive study yet of heat-related mortality in Washington state, and the first to look beyond the major population centers to include rural areas.
Statewide, the odds of dying were on average 8% higher in recent decades on days when the combination of temperature and humidity, known as the humidex, was in the top 1% of recorded values at that location, compared to a day with a mid-range value for humidex.
“This study shows that heat-related mortality, even in a temperate area like Washington state, is a current environmental public health problem,” said lead author Logan Arnold, who did the work as a UW master’s student in quantitative ecology and resource management.
Effects of heat on underlying health conditions
Although heat stroke is sometimes listed as the official cause of death, other conditions exacerbated by heat are often the immediate focus. Researchers used statistical methods to uncover “hidden” deaths that may have listed something else, like illness or a chronic disease, as the primary cause.
“This research adds to existing evidence that the burden of heat-health impacts resides in the effect on underlying health conditions,” said senior author Tania Busch Isaksen, associate teaching professor in UW Department of Environmental & Occupational Health Sciences. She is also co-director of the UW Collaborative on Extreme Event Resilience.
“For example, we see an increase in diabetic and cardiovascular-related mortality associated with extreme heat days,” she said. “Physiologically, it is harder for people with underlying health conditions to thermoregulate, but it is also likely that medications play a role in the body’s ability to dissipate heat.”
'Place really matters'
The study analyzed deaths from 1980 to 2018 recorded by the Washington State Department of Health. The authors included only non-traumatic deaths in the months of May through September and separated them into 10 federally defined climatic zones. Exposure to heat on the day of death was determined based on home address and the humidex on that date.
The mortality rate on days with humidex in the top 1% of historical values was significantly higher for four climate zones: the Puget Sound lowlands, which includes Seattle and other major cities; the east slope Cascades, circling Puget Sound but farther inland; Northeastern, which borders Canada and Idaho and includes the city of Spokane; and the Northeast Olympic San Juan, which includes all the San Juan Islands, Port Townsend and a coastal stretch of the Olympic Peninsula.
“Place really matters. You can’t just apply what we’ve seen from other parts of the U.S. to what’s happening here,” Busch Isaksen said. “That’s why local research is critically important to understanding environmental risks.”
The increase in mortality in places with more moderate climates, the authors suggest, could be because these areas are less prepared for heat, meaning they are less physically adjusted to heat and have fewer protective behaviors; or have less adaptative infrastructure like air conditioning or access to cooling centers.
Additional co-author is Mark Scheuerell, a UW associate professor of aquatic and fishery sciences.