When extreme weather and natural disasters such as wildfires and hurricanes descend on a region, the immediate concern is typically damage from the event itself. But the power outages that often accompany such events can be dangerous as well. The recent Los Angeles wildfires left hundreds of thousands of residents without power, and Hurricane Helene caused more than 5 million customers in the Southeast to lose power last fall.

A new study published in PLOS Climate is among the first to parse how different kinds of extreme events affect the power grid in the United States.

“We see that power outages are occurring much more frequently with severe weather events than without, even compared to, like, 10 years ago,” said Vivian Do, an environmental health scientist at Columbia University and a paper coauthor.

Do and her colleagues found clear regional differences among the types of events associated with outages and gave insights into which kinds of weather are most dangerous for the grid.

Knowing, for example, that heavy rain is more likely to knock out power than severe heat or that extreme cold and heavy snowfall together are more dangerous than either by itself could let residents and authorities better prepare for outages.

The Worst Time for an Outage

Planning for outages that happen at the same time as severe weather is hampered by a lack of data on how specific weather and power outages relate in a given area, despite the increased risks these overlapping events bring, Do said. City agencies can assist residents who lose power by offering vital services at shelters, for example, but their strategy is likely to differ when a few feet of snow blankets the ground. “There are so many nuances to preparedness, to response,” she explained.

Knowing which scenarios are more likely to affect an area is a necessary first step toward devising strategies to deal with outages.

The researchers compiled county-level data from poweroutage.us, a service that aggregates data on outages from utilities around the country, and compared them with occurrences of wildfires, extreme heat and cold spells, heavy rain and snowfall, and hurricanes.

Between 2018 and 2020, 73% of counties in the dataset saw at least 1 day when a severe weather event and a power outage coincided. Further, 54% of counties overall, in 45 states, had at least one instance in which two simultaneous natural events occurred at the same time as an outage.

Their data did not allow them to prove any outage was directly caused by a severe event, only that they happened at the same time. Many of the natural events they analyzed are not independent of one another—hurricanes can bring heavy rain and wind, for instance—making it difficult to tease out which, if any, contributed to an outage or dealt the final blow.

Overall, the events most likely to coincide with an outage were hurricanes, followed by snowstorms and heavy rain, though the association varied by region: Rain was a bigger factor in the Northeast and on the Gulf Coast, as well as in Michigan and Southern California, whereas extreme heat events paired with power outages were concentrated in Southeastern states. Heavy snow coinciding with outages occurred most often in counties in the Northeast and in some counties near the West Coast. And though hurricanes were most likely to be associated with an outage, severe rain coincided with the most outages across the country overall.

Simultaneous severe weather events raised the probability of an outage even more. Of these events, paired severe heat and rain coincided most often with outages across the United States, whereas hurricanes and rain and severe cold and snow were the next most common paired weather combinations associated with outages. Some counties even saw three simultaneous hazards coincide with outages, such as extreme heat, rain, and hurricanes or severe cold, snow, and wildfires.

Bolstering the Grid

Multiple studies have shown that power outages alone can increase threats to human health—from spoiled food to failing medical equipment to a loss of heat in winter. These threats become more dire when paired with severe weather.

This kind of information could be useful to utility companies, which must allocate finite resources for maintenance and repair and make plans for a range of scenarios, said Ken Cummins, a researcher at the Florida Institute of Technology with experience in grid reliability who wasn’t involved in the research. (Cummins is a former science adviser to Eos.) But he cautioned that the specific infrastructure used by local electric utilities, which can vary significantly, is also an important factor.

“One thing that would be a problem in St. Louis might not be a problem in Denver or Omaha and would certainly be a different problem in New York City or Long Island,” he said.

Do agreed that a local approach to preparing for both severe weather and outages is paramount, something she argued their research is helping to advance by beginning to prioritize threats. “Preparedness and response should really be nuanced and consider how the different combinations can bring up different problems for different populations,” she said.

Cummins questioned why thunderstorms weren’t included in the analysis, given that they are the main cause of outages in many places. Though rain, snow, and other kinds of weather play a role, “thunderstorms today outweigh the impact of those things all added together,” Cummins said. “They are the majority of outage hours over the United States.”

Do said they considered including lightning strikes, but too few have caused outages to prioritize them. However, phenomena such as high winds and hail from thunderstorms, which also cause outages, did not feature in their analysis. That may be a direction for future work. “A lot of the research in this particular field is still very much so in its exposure assessment phase,” Do said.

This article originally appeared in EOS Magazine.