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How much more dangerous is 110 than 105? A lot, data shows

Woman pours water on herself from bottle
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There is an excessive heat warning in effect in Phoenix through Friday with high temperatures expected to be around 114 degrees or hotter. But how much more dangerous are temperatures when they rise that high? New data from the Maricopa County Department of Public Health provides some insights.

The recent report analyzes five years’ worth of hospital visits for heat-related illnesses — everything from heat cramps and heat rashes to severe heat stroke.

The report’s authors found that when high temperatures increased from 105 degrees to 110 degrees, cases of heat-related illness spiked 76%. And when temperatures were above 115 degrees, hospital visits for heat-related illnesses were 129% more frequent than they were on 105-degree days.

“It’s not terribly surprising if we're thinking of heat as the positive factor for people being ill, that as it gets hotter, more people get ill, and that's what we see in this data,” said Dr. Nick Staab, assistant medical director for Maricopa County Public Health.

Above-normal nighttime temperatures played a role, too, Staab said. 90-degree nights resulted in 140% more heat-related illness cases than 80-degree nights.

“It just doesn't give the body enough time to recover from those really high temperatures that we're experiencing during the day. So we also see increased heat-related illness related to those high overnight lows,” Staab said.

On average, Phoenix gets 21 days per year with high temperatures at or above 110 degrees, according to the National Weather Service. As of Monday, Phoenix has already had 21 days that hot this year, with more extreme heat still to come. Last year, Phoenix had a record 55 days at or above 110 degrees.

The long stretches of extreme heat in 2023 led to a record-shattering 645 heat-related deaths in Maricopa County, but above-average temperatures this summer could lead to even more fatalities. 13 heat-related deaths have been confirmed so far this yearin Maricopa County with more than 160 others under investigation. That’s more than 50% increase from the same point last summer.

The new report on heat-related illnesses considers data from 2018 to 2022. During that time, the county saw an average of 2,387 heat-related illness cases per year. But Staab expects those numbers have also climbed.

“Certainly with the trends that we saw in 2023, and then now with this summer with our temperatures being higher and our heat-related deaths being higher, I would be pretty certain that we would continue to see increases in heat related illness,” Staab said.

The report shows men experience heat illnesses at twice the rate of women in Maricopa County. People with cardiovascular diseases and chronic kidney disease were at increased risk for these illnesses. Alcohol and drug use also increased people’s risk. And people experiencing homelessness faced 100 times greater risk for heat-related illnesses than the general population, the report says.

But Staab said everyone in Maricopa County should understand the threat that extreme heat poses.

“Have a plan, make sure you can get out of the heat and to a cool space, and make sure you stay well hydrated when we're experiencing these high temperatures,” Staab said. “Make sure that you're calling and checking on friends, neighbors, family members who are at high risk, making sure that they have functioning air conditioning and that if they don't that they have a plan for staying cool.”

Katherine Davis-Young is a senior field correspondent reporting on a variety of issues, including public health and climate change.