Heat is the top weather-related killer in the US. Why ranking heat waves could save lives

The World Meteorological Organization has no plans to name heat waves, but one organization believes categorization could save lives.

Hurricanes on a 1 to 5 intensity scale are given names like "Alex" and "Dorian." The Weather Channel names winter storms. But what about categorizing and naming extreme heat waves?  

Extreme heat kills more than 600 people in the U.S. annually. NOAA ranked heat as the top cause of weather-related fatalities in the nation in 2021. 

As heat waves intensify globally, the Adrienne Arsht-Rockefeller Foundation Resilience Center believes naming and ranking them on a 1 to 3 severity scale using health-based metrics could save lives. It’s a concept the Arsht-Rock Resilience Center, which works to implement climate-change solutions, is piloting in:

  • California
  • Miami
  • Kansas City, Missouri
  • Madison and Milwaukee, Wisconsin
  • Athens, Greece
  • Seville, Spain, which became the first city worldwide to name a heat wave: Zoe.

“It affects every person everywhere, and people don't have to die from heat,” Arsht-Rock Resilience Center director Kathy Baughman McLeod told USA TODAY, adding that, for now, U.S.-based cities are only categorizing heat waves, as they monitor Seville's progress with naming them. 

Here’s what to know about the the concept, who's on board and how two states are piloting it. 

How does a heat-wave ranking system work?

To create a categorization system, Arsht-Rock’s team examined decades of data showing daily deaths from any cause. They layered the data with climate information to observe whether heat was a factor on dates with higher death tolls, said Arsht-Rock communications director Geraldine Henrich-Koenis.

“Let's say 10 people on average died every day for different types of causes; we saw that on days where humidity, nighttime temperatures, etc. reached a certain level, there was a spike in the number of deaths for that day,” Henrich-Koenis told USA TODAY.

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Unlike tropical storm categories based on the storm's intensity, each heat wave category level – Category 1, Category 2 and Category 3 – is based on thresholds for the expected rise in all-cause mortality for each location when temperatures rise, according to Henrich-Koenis. Those category thresholds vary based on different cities' sensitivity to heat, she explained.

"When we say, 'with a Category 1 heat wave, we expect an increase of up to 20% in all-cause mortality,' of a baseline of 10 people, we can expect up to 20% more people will die because of heat," she said. 

Why isn't the World Meteorological Organization on board?

The WMO announced that it does not plan to rank or name heat waves. What’s been established for tropical cyclones may not necessarily translate to naming heat waves, the WMO said. 

“Independent practices to rank and name heat waves which are not coordinated with the official warning systems may risk disrupting civil protection protocols and coordination efforts, bring unintended negative consequences or reduce the effectiveness of established heat advisory and response measures,” the WMO's statement read.

Baughman McLeod said she's "optimistic" Arsht-Rock and the WMO can work together. She added, "It's also a health issue, this climate hazard goes beyond meteorological realm, so we're going to need both approaches."

California bill could protect millions from extreme heat

Los Angeles County experienced record-breaking heat as high as 121 degrees Fahrenheit in 2020, according to the California Department of Insurance. Assembly Bill 2238, first introduced in February, would launch a first-of-its-kind statewide extreme heat advance warning and ranking system for more than 39 million Californians. The proposed bill is in partnership with Arsht-Rock. 

It would require the California Environmental Protection Agency to develop a ranking system that could take effect in late 2023 if the bill is approved by legislature by Aug. 31 and signed into law, said California Insurance Commissioner Ricardo Lara. The system's focus would be on ranking rather than naming, he explained.

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"We need to build public awareness about the severity of heat waves, and naming them wouldn't give us that sense of urgency," Lara told USA TODAY, adding that air quality or fire danger ranking systems work without naming. "Too often, stories in terms of heat waves or extreme heat are treated as just a weather story when it's really a public health emergency."

California hasn't laid out what their ranking system will look like. Leaders plan to work with the National Weather Service and climate experts to develop it once the bill becomes law, according to Lara.

Wisconsin pilots heat wave warning system with National Weather Service

The urban heat island effect has hit Wisconsin cities like Milwaukee and Madison, said Gavin Luter, director of UniverCity Alliance at the University of Wisconsin-Madison. In April, the college invited climatologist Larry Kalkstein to explain excessive heat’s impact on human health and the benefits of ranking heat waves.

Luter and Kalkstein are part of the Wisconsin Heat Health Network, which is collaborating this summer with the National Weather Service office in Sullivan, Wisconsin, to pilot an excessive heat warning system. The pilot program is also part of Arsht-Rock's partnership.

The system factors into account mortality and weather data and could help policymakers decide how to keep people healthy during extreme heat, according to the University of Wisconsin-Madison. 

“Oftentimes when there's a heat event that might not seem too intense but it comes right after a cool period, people might go, ‘okay, it's going to be really hot,’ but actually, those are more dangerous events for human health, based on historical data,” Luter told USA TODAY.

“What the NWS in Sullivan is trying to work on is how can we change the messaging so people know this is an event that could be more dangerous based on the kind of air mass that exists."