A wide-ranging study published on Tuesday in Environmental Sciences and Technology was the latest such reminder. Researchers concluded that the consequences of an electrical grid failure during a Phoenix summer heat wave could be dire.
More than half of the city's population, according to the study, would require emergency care in the case of a multi-day blackout during a heat wave. Resulting deaths could number in the thousands. It was "quite an alarming number," David Hondula, a researcher at Arizona State University and one of the authors of the study, told The New York Times.
The study arrives alongside a new forecast from the National Weather Service that says Arizona will see above-average temperatures this summer. In April, Mayor Kate Gallego called for additional federal aid during extreme heat waves.
Welcome back to summer in Phoenix.
Half of Phoenix could be hospitalized in blackout
The published study — "How Blackouts during Heat Waves Amplify Mortality and Morbidity Risk" — was a collaboration between researchers at ASU, the University of Michigan and the Georgia Institute of Technology. It estimated how an electrical blackout during a heat wave might affect three cities: Phoenix, Detroit and Atlanta.
Electrical grid failures are becoming more common — more than doubling nationwide between 2015 and 2020, the researchers noted. In Arizona, power companies across the state have said they are also concerned that they will be increasingly vulnerable to blackouts.
The study modeled a blackout in which all residents lost power for two days and then saw power restored gradually over three days. Changes to the risk of mortality were then measured. The researchers estimated that in Phoenix more than half of the population of the city would require emergency care in the case of a heat wave.
That number was far greater than those of Detroit or Atlanta. The discrepancy, the researchers wrote, reflected "the extremity of heat exposures in a desert city in the absence of mechanical AC."
The study also suggested some potential mitigation measures. Additional tree canopies and shade — which residents have long fought for in Phoenix — could reduce mortality risk by as much as 27% in the city during a heat wave, the researchers found. Cool roofing — reflective roofs that help reduce the urban heat island effect — also would have an impact.
As climate change means hotter summers in Phoenix, the researchers noted, the risk of blackouts will only grow.
Above-average heat expected
Summers usually feel extreme in Phoenix. But according to the National Weather Service's latest seasonal outlook, residents in the Valley should brace for even hotter-than-average weather in June, July and August.
The entire state of Arizona is expected to experience above-normal temperatures, according to the NWS map. The eastern side of the state, in particular, is likely to see a hotter summer. "There's a 60% to 70% probability that it'll be warmer than average in that region," Johnna Infanti, a meteorologist with the NWS Climate Prediction Center, told Phoenix New Times.
Phoenix, too, is likely to see above-average heat. The city is forecast to see a daily maximum temperature this summer of 104 degrees.
Expected low rainfall is one of the reasons that the Southwest is likely to see a hot summer, Infanti explained. "Part of it has to do with low soil moisture and the fact that there's also a chance of below-normal rainfall in the region," she said.
The NWS map predicts that Phoenix will see slightly less precipitation than usual this summer, even after an abnormally rainy spring.
And for many — particularly unsheltered people in Phoenix — extreme heat can prove deadly, with or without a blackout.
So far this year, there have been four confirmed deaths from heat exposure in Maricopa County, with a dozen more under investigation, according to the latest data from the Maricopa County Department of Public Health. The first death was recorded on April 11.
In 2022, there were 425 heat-associated deaths in total, a 25% increase from 2021. More than 40% of those deaths were among people who were homeless.
In her State of the City address in April, Gallego called for the Federal Emergency Management Agency to recognize extreme heat as a natural disaster, which could free up previously unavailable federal funds for emergency responses to extreme heat.
For now, though, the city will have to manage on its own.