by Background: Global warming is intensifying both threats.
As humans warm the planet, both heat waves and wildfires are becoming more severe and longer-lasting in the American West. That also means they are more likely to overlap. Researchers have estimated that two-thirds of California’s land area experienced scorching heat and dense wildfire smoke at the same time at some point during the state’s record fire year, 2020.
Both hazards are harmful to health on their own: heat stress increases heart strain, and inhaling wildfire smoke can aggravate lung conditions. The new study, led by researchers at the Scripps Institution of Oceanography at the University of California, San Diego, looked at the health effects when the two threats appeared together.
On exceptionally hot, smoky days, staying indoors doesn’t always help, and certainly not for people who don’t have air conditioning and air purifiers, said Tarik Benmarhnia, an environmental epidemiologist at Scripps and one of the study’s authors. “Air pollution doesn’t stay politely outside,” he said. “It gets in, it interacts with a lot of indoor air pollutants, and it can cause a lot of problems.”
The results: Aggravating and also unequal damages.
Researchers took state data on unscheduled hospitalizations between 2006 and 2019 and combined it with detailed readings of wildfire temperatures and smoke.
They found that combined exposure to the two hazards had a greater effect on hospitalizations than the sum of the effects of each separately. In other words, the health damage caused by simultaneous heat and smoke was greater than the sum of its parts.
The researchers found that California’s agricultural heartland, the Central Valley and its forested northern tip experienced more hot, smoky days than other regions during the study period.
They also found that the size of the composite effect of heat and smoke varied between communities with different demographics. Areas with weaker socioeconomic indicators and higher proportions of nonwhite residents fared worse.
What could be next?: Joint warnings for heat and smoke.
At the moment, heat advisories in California come from local National Weather Service offices, while local air quality management districts issue hazardous air warnings.
The study’s findings suggest that a joint heat and smoke warning would help keep more people safe, Dr. Benmarhnia said. To account for the added danger on sweltering days, officials could also consider issuing air quality alerts even when pollution has not reached the level that would trigger a warning on colder days, he said.
A spokeswoman for the California Air Resources Board said the agency was preparing new educational resources this year to help residents protect themselves from simultaneous heat and smoke.
“These types of joint events are going to happen more and more,” Dr. Benmarhnia said.
