University of Washington: Heat-related mortality risk is widespread across Washington state, study shows
Heat-related deaths are an issue across Washington state, and they occur even in regions that typically have milder climates, according to a University of Washington study published Aug. 30 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. “It’s not a future public health problem that will exist in a warming climate — it’s something that we are already experiencing now.”
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, a UW associate teaching professor in environmental and occupational health sciences and co-director for the UW’s Collaborative on Extreme Event Resilience. “For example, we see an increase in diabetic and cardiovascular-related mortality associated with extreme heat days. 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.”
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.
Results support what previous studies in King County have shown: Heat does lead to more deaths, even in places with milder climates.
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.
Although the total number of deaths in the Northeast Olympic San Juans zone was lower than in the other three regions, that region had an especially sharp increase with rising humidex.
“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 other climate zones didn’t necessarily lack risk, but didn’t have enough mortality data to obtain a statistically certain trend.
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.
Although the total number of deaths in the Northeast Olympic San Juans zone was lower than in the other three regions, that region had an especially sharp increase with rising humidex.
“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 other climate zones didn’t necessarily lack risk, but didn’t have enough mortality data to obtain a statistically certain trend.