Extreme Heat Warnings May Not Be Working

(Bloomberg) -- Summertime heat advisories have one job: Warn people when extreme temperatures could be harmful to their health. By that standard, they may be failing cooler parts of the country, according to new research.

Local public-health officials send the alerts based on National Weather Service data and criteria set with local weather officials. They vary widely based on region. The study found that in the Southwest, weather alerts go out, on average, before people start showing up at emergency rooms for heat-related disorders. Across the central-northern band of the U.S., it’s the reverse. When the local heat index (a combination of temperature and humidity) nears about 108 degrees Fahrenheit, alerts should go out; yet hospital data reveal that people show symptoms of heat stress when the index is about 10 degrees cooler.

The study, published Tuesday in the Proceedings of the National Academy of Sciences, suggests better understanding of the health and weather data would help officials design communication strategies that avert illness. Ascertaining the effectiveness of the alerts “has been elusive, complicating the work of setting appropriate local warning thresholds,” according to new research from the U.S. Center for Disease Control and Prevention scientist and several other institutions.

To figure out how well alerts are aligned to actual weather, the researchers assembled data on roughly 50 million inpatient hospitalizations, from 1,617 counties in 22 states, from the summers of 2003-2012. High heat caused jumps in instances of kidney disorders, dehydration, cardiovascular and respiratory diseases and diabetes, the study found. 

The fourth U.S. National Climate Assessment, released in November, projects the average temperature may rise about 2.5 degrees Fahrenheit (1.4 degrees Celsius) over the continental U.S. in the period from 2021-2050, relative to 1976-2005, “implying recent record-setting years may be ‘common’ in the next few decades.”

The new research is retrospective and does not address how getting heat alerts right may become more critical as overall warming continues. The study also does not account for non-meteorological factors that influence public health during heatwaves, like the prevalence of air conditioning. Alert-fatigue—when people ignore warnings because there are too many of them—is also a concern.

The study represents an arduous first step in making sure the criteria for sending alerts are based on public-health data. As the authors say, “[I]t is not clear exactly where warning thresholds should be set.”

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