Heat wave classification, naming system under construction


The tale becomes all too familiar: a severe heat wave develops, and a few days later people die. Today, lawmakers, scientists and a think tank are coming together to better adapt to America’s leading weather-related killer – categorizing and naming them in big cities.

In January, California Insurance Commissioner Ricardo Lara and other delegates will formally introduce legislation to assess and name heat waves in Los Angeles, potentially establishing the nation’s first ranking system for heat waves. Categorization would help communities take preventative action and hopefully reduce the number of heat-related deaths.

Heat waves are having a particularly strong impact in Southern California, where they have become more frequent, intense, and long-lasting over the past five decades. By 2050, Los Angeles is expected to experience an average of 22 days of extreme heat, up from six days from 1980 to 2000.

“This is a climate change adaptation and resilience strategy,” said Kathy Baughman McLeod, director of the Resilience Center at the Adrienne Arsht-Rockefeller Foundation which helps lead the initiative. “We are doing what we can do now to protect people’s lives and livelihoods. And that means being aware of the risks they face and what they can do to protect themselves.”

Los Angeles is one of six pilot sites that the Arsht-Rockefeller Center is working with along with Kansas City, Milwaukee and Miami-Dade County as well as Athens and Seville, Spain. The center aims to improve communication and public recognition of heatwave threats. In August 2020, the center formed the Extreme Heat Resilience Alliance, a group of emergency response organizations, researchers, cities and nonprofits fighting against the dangers of urban heat.

While the concept is similar to evaluating a hurricane, this ranking system would instead rank heat waves according to expected health outcomes.

“It is, if not the only one, at least one of the very few outcome-based weather warning systems,” said Larry Kalkstein, chief science adviser at Arsht-Rockefeller Center. “It’s the number of people who are going to die, rather than saying it’s going to be 105 degrees.”

Kalkstein and his team are creating three categories of heat waves for use in major US cities. Category 1 would indicate a relatively low number of expected deaths, perhaps a zero to 10 percent increase in daily mortality. Category 3 would indicate a larger potential increase in the number of deaths, such as the Pacific Northwest heat wave in June.

Each category would be linked to specific actions that can help alleviate the effects of extreme heat. For example, a category 3 could lead to the opening of urban swimming pools and air-conditioned shelters or even knocking on doors and monitoring the elderly and other vulnerable groups. Local utilities could be prevented from shutting off air conditioning or electricity for non-payment during episodes of intense heat. Other protections could include changing the hours of workers who have to work outside the home.

Kalkstein and his colleagues are awaiting the green light from the National Weather Service, the only government agency that could announce official heatwave alerts and categories, to conduct pilot studies. The goal is to create an interactive website, accessible by the weather service and stakeholders, that automatically checks for forecast updates every 15 minutes or so.

“We want to be able, by next summer, to try this system out in these different cities… then if they are successful, the goal, of course, is to do it nationally,” Kalkstein said.

The team already has permission from the local government to run pilot programs in Athens and Seville next summer.

A heat wave originates from a large three-dimensional air bubble, sometimes described as thermal domes. But not all air masses are the same and can pose different threats. Some are hot and humid, created by the warm tropical air offshore. Some are hot and dry, native to the deserts of the southwestern United States

Kalkstein and his team conducted detailed statistical analyzes of how weather conditions affect mortality in two of the pilot cities, Kansas City and Milwaukee. In Kansas City, they found 41 heat waves that have resulted in higher mortality since 1975 using this air mass approach along with other weather factors, such as air mass persistence.

For example, their calculations showed that a heat wave in July 1980, which lasted 17 days, showed an average increase in mortality of 425% over the period – an increase of about 25% in mortality from day.

In Milwaukee, they found 31 such heat episodes since 1975. For a heat wave in July 1995, they calculated an average increase in mortality of 212 percent during the six-day event, or a average daily increase of 35 percent.

In general, Kalkstein said warm, humid air masses and hot, dry air masses are generally associated with higher mortality.

In addition to classifying the heat waves, the pilot cities will also experiment with their name. Baughman McLeod said deciding on the name of the heat waves is more of a study of human behavior and is working with a social marketing company, which has helped test the names of the focus groups. For example, some rejected the idea of ​​naming heat waves after local flora and fauna, saying they would not take heat waves seriously.

“My prediction is that a human name or a set of Greek names that actually reflect human beings will be where people land,” said Baughman McLeod. “But we are putting in place a process to answer that question.”


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