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WASHINGTON – The growing risk of overlapping heat waves and power outages poses a serious threat for which major U.S. cities are unprepared, new research suggests.

Power outages have increased by more than 60% since 2015, even as climate change has worsened heat waves, according to the new study published in the journal Environmental Science & Technology. Using computer models to study three major U.S. cities, the authors estimated that a combined blackout and a heat wave would expose at least two-thirds of those cities’ residents to heat exhaustion or a heat wave. heatstroke.

And although each of the cities in the study has dedicated public cooling centers for people who need heat relief, these centers could not accommodate more than 2% of a given city’s population, they said. the authors found, leaving an overwhelming majority of residents at risk. .

“A widespread power outage during an intense heat wave may be the deadliest weather event we can imagine,” said Brian Stone Jr., professor in the School of City & Regional Planning at the Georgia Institute of Technology and author principal of the study. . Yet such a scenario is “more and more likely,” he said.

Climate change also appears to make power outages more frequent. From 2015 to 2020, the number of annual outages in the United States doubled, Dr Stone said. And those power outages were more likely to occur during the summer, suggesting that they were in part due to high temperatures, which increases demand on the power grid when people turn on their air conditioners.

As heat waves and power outages become more and more frequent, “the likelihood of a simultaneous heat wave and blackout event is very likely also increasing,” said Dr Stone.

So Dr Stone, along with a team of eight other researchers – from Georgia Tech, Arizona State, University of Michigan, and University of Guelph in Ontario, Canada – set out to assess the human health consequences when Power outages coincide with heat waves. .

To do this, they chose three major cities – Atlanta, Detroit, and Phoenix – and looked at the temperatures recorded during some of their most severe heat waves.

Then they used computers to model temperatures in different neighborhoods if those heat waves were to strike at the same time as a city-wide power outage turned off air conditioners.

Basically, the researchers wanted to know how hot the interiors of homes would get under these conditions – something that Dr Stone said had never been tried before. They collected data showing the building characteristics for each residential structure in each city – for example, the age of the building, the materials of construction, the level of insulation and the number of floors.

The results were alarming. In Atlanta, more than 350,000 people, or about 70% of residents, are said to be exposed to indoor temperatures of 32 degrees Celsius (89.6 degrees Fahrenheit) or more, the level at which the National Weather Service’s thermal classification index indicates. heat exhaustion and heat stroke are possible.

In Detroit, more than 450,000, or about 68 percent, are believed to be exposed to this indoor temperature. In Phoenix, where a large majority of residents depend on air conditioning, the entire population is believed to be at risk – nearly 1.7 million people.

Even without a power outage, some residents in every city do not have access to air conditioning, exposing them to dangerous indoor temperatures during a heat wave. Those numbers range from 1,000 people in Phoenix to 50,000 in Detroit, depending on the characteristics of their homes, the authors found.

This exposure is more pronounced for lower income households, which are 20% less likely to have central air conditioning than higher income households.

The authors reported that each city had designated public cooling centers for extreme heat. But they found that in each case, these centers could only accommodate 1 to 2 percent of the total population.

And none of the three cities require these cooling centers to have back-up generators to run air conditioners in the event of a power failure.

“Based on our results, a simultaneous heat wave and power outage would require a much larger network of emergency cooling centers than is currently established in each city, with mandatory back-up power generation. », Wrote the authors.

The New York Times has asked officials in Atlanta, Detroit and Phoenix to comment on the newspaper’s findings and outline their plans to respond to a combined blackout and heat wave.

A spokeswoman for the city of Phoenix, Tamra Ingersoll, said that in a crisis situation such as an overlapping heat wave with a prolonged power outage, many residents would leave the city on their own. Emergency response for those who remained would focus on “vulnerable populations such as the elderly, infirm or low-income,” she said.

Christopher Kopicko, spokesperson for the Detroit Office of Homeland Security and Emergency Management, said only one of the city’s 11 cooling centers had a back-up generator. But he said Detroit recently bought mobile generators that could be sent to cooling centers that needed them and that residents could go to any of the city’s 12 police stations, which have back-up generators. . He also said some of the city’s largest sites had agreed to serve as mass shelter sites.

The office of Atlanta Mayor Keisha Lance Bottoms did not comment.

The Federal Emergency Management Agency, in response to questions about its intention to help a major city cope with a combined blackout and heat wave, referred to a 2017 plan to deal with the effects of a long-term power failure.

But that paper did not address how the agency would react if a heat wave were to occur during such a power outage, in addition to noting that “the lack of electricity will create challenges in providing constant heat or cooling. and adequate sanitation / hygiene in shelters or other mass health care facilities. “

Other cities in the United States are at risk of facing similar health threats from a combined heat wave and power outage, in terms of the share of their population that could most likely be at risk , noted the authors.

“We are finding that millions of people are at risk,” Dr. Stone said. “Not years in the future, but this summer.”

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