The unhoused and elderly are extremely vulnerable in Phoenix heat wave

The intense heat wave that continues to engulf the Valley has the potential to hospitalize anyone who spends too much time outside — but it can quickly turn deadly for vulnerable residents.

Why it matters: People experiencing homelessness and senior citizens have heightened risks of developing heat-related illness, medical and climate experts tell Axios.

• Of the 425 people who died of heat-related causes last year, at least 178 were experiencing homelessness.
• Nearly two-thirds were 50 or older.

Between the lines: People experiencing homelessness are obviously at risk of heat exposure because they lack shelter. But they also have high rates of chronic illnesses, substance abuse and other conditions that can be complicated by heat.

• Older adults are more likely to have heart or kidney issues that make them prone to heat illness and take medications for those conditions that can cause dehydration, said Patrick Vinck of Oak Street Health in Apache Junction, which has a large elderly population.

By the numbers: Between July 1 and July 12, Phoenix received 230 9-1-1 calls related to heat, according to the city's chief heat officer David Hondula.

• That's about 30% fewer calls than the city got during a comparable 12-day heat streak last summer, but Hondula noted this heat wave's most extreme weather is likely still to come this weekend.

What's happening: If forecasted temperatures are correct, we will break the streak of 110-plus-degree days early next week, per the National Weather Service.

• We may also break the streak of overnight low temperatures above 90 degrees.

Threat level: It's high overnight temperatures that are most dangerous for people without shelter or reliable AC, as there's no time for the body to recover from daytime extreme heat, NWS meteorologist Tom Frieders told Axios Phoenix.

Reality check: Metro Phoenix has dozens of indoor respite centers, but only one — the Brian Garcia Welcome Center at the Human Services Campus — is open 24 hours per day.

• This means most people without shelter or air conditioning are left without an option at night.

Go deeper: 400 promised homeless shelter beds aren't ready for summer heat

What they're saying: "We know there will be hundreds of people living on the street through this heat event who are at much, much, much higher risk than nearly everyone else in the population," Hondula said.

What's next: Phoenix Mayor Kate Gallego and other officials are pushing FEMA to add extreme heat to its list of declared emergencies.

• That would unlock resources that could allow the Valley to operate more overnight heat respite centers, Hondula said.