The toll of heat deaths in the Phoenix area soars after the hottest summer on record

The toll of heat-associated deaths in Arizona's most populous county—still being tallied after the area's hottest summer ever recorded—has soared over 360, alarming public health officials who say the final count will surely set a new record.

Maricopa County, the hottest metropolitan area in the U.S. and home to Phoenix, reported this week that 361 heat-associated deaths have been confirmed this year as of Oct. 7. Another 238 deaths remained under investigation.

As of the same time last year, 331 heat-associated deaths had been confirmed, with another 126 deaths still being studied. No other major metropolitan area in the U.S. has reported such high figures or spends so much time tracking and studying them.

"It definitely looks like we'll see more deaths than last year and maybe even more than 500," said Dr. Rebecca Sunenshine, medical director for Maricopa County Public Health. "But we won't really know until the end of the season."

Maricopa County set an annual record last year with 425 heat-associated deaths confirmed.

This summer, Phoenix experienced the hottest three months since record-keeping began in 1895, including the hottest July and the second-hottest August. The daily average temperature of 97 F (36.1 C) in June, July and August passed the previous record of 96.7 F (35.9 C) set three years ago.

Phoenix also set a record in July with a 31-day streak of highs at or above 110 F (43.3 C).

Sunenshine said Maricopa County began tracking heat-associated deaths in 2005, then gradually began collecting additional information, including the age, sex, race and ethnicity of those who died and whether they were indoors or outside when they got sick.

Investigators also began noting whether those who died inside had an air conditioner, whether it was working and whether there was electricity to power it. Sunenshine said collecting that kind of information has led to rules requiring regulated power companies to keep the electricity running during hot spells even if the bills haven't been paid.

"It's really important to know the circumstances around these deaths," Sunenshine said. "It can lead to policy changes."

The number of people dying from heat-related causes has risen not only in the Phoenix area, but across the U.S. and around the world as climate change makes heat waves more frequent, intense and enduring.

Counting such deaths can take months of investigation, including toxicological tests, to determine whether heat was a contributing factor in someone's death. The deaths Maricopa County tallies include ones that were the direct result of high temperatures, such as heatstroke, as well as ones in which heat was a contributing factor, such as a heart attack provoked by the hot weather.

Approximately three-fourths of the heat-associated deaths in Maricopa County so far this year year were outside. About 44% of those who died were people experiencing homelessness in a county where an estimated 10,000 don't have permanent housing. More than a third of all the people who died were 65 or older.

There have been 89 indoor heat deaths in the county confirmed so far, mostly in homes where the air conditioning was not working or turned off.

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