HeatRisk Forecasts and Heat-Related Emergency Visits in New York, 2024

Heat exposure is linked to harm to health, including heat-related illness. In spring 2024 the National Weather Service, working with CDC, released HeatRisk for the continental United States: a health-based heat forecast issued up to 7 days before hot weather. It rates each place on a five-level color scale, from 0 (green, little to no risk) to 4 (magenta, extreme risk). The scale takes account of the particular heat risks of different places and times of year, and of how long the heat lasts, including temperatures at night.

That first summer, the New York State Department of Health checked whether the forecasts tracked what actually happened in its emergency departments. The results were published in CDC's Morbidity and Mortality Weekly Report as a Notes from the Field report.

Background: a warming state

Average temperatures in New York rose by about 2.6°F (1.4°C) from 1901 to 2022. The state's heat preparedness work has included studying how heat relates to health outcomes, calibrating heat advisory thresholds to their health effects, and building partnerships for heat mitigation and adaptation.

How the comparison worked

For May through September 2024, the department took the daily 24-hour HeatRisk forecast for each of the 57 counties outside New York City. It then counted emergency department visits for heat-related illness recorded in its Electronic Syndromic Surveillance System. A visit counted if it carried a diagnosis code for effects of heat and light, exposure to excessive natural heat, sunburn or exposure to sunlight, or if the patient's chief complaint was something like sunstroke, heatstroke, heat exhaustion or sunburn.

Visits were matched to the forecast for the same county and day. For each of seven regions, and for the state outside New York City as a whole, the analysts calculated a visit rate for each HeatRisk level: little to no risk, minor, moderate, major and extreme. The report describes this as an ecological analysis.

What they found

• Most days were low risk. In every region, at least 79% of county-days were forecast at little-to-no or minor risk, and no region had more than 0.3% of county-days at extreme risk.
• Higher forecasts, more visits. In six of the seven regions, and in the state outside New York City overall, forecasts of higher risk went with higher rates of emergency visits for heat-related illness.
• Extreme-risk days were rare. In the Capital District region there were no heat-related emergency visits on the few county-days forecast at extreme risk. The Hudson Valley, Long Island and Northeast regions had no extreme-risk county-days at all, though in each the visit rate still climbed with every level up to major.

What it means

The authors conclude that HeatRisk can help raise awareness of the health risks of heat. It gives state and local agencies a basis for acting, and helps the public and health professionals take steps to limit exposure. Building HeatRisk into weather apps on mobile phones might make it easier to reach, and they call for further study of other uses, such as an early-warning tool to prevent heat-related harm.

Sources

• Neil A. Muscatiello, Wanhsiang Hsu, Heather Aydin-Ghormoz, Charlene Weng, Vajeera Dorabawila, Kathleen F. Bush and Ambarish Vaidyanathan, "Notes from the Field: HeatRisk Forecasts and Emergency Department Visits for Heat-Related Illness — New York, May–September 2024," Morbidity and Mortality Weekly Report, CDC: https://www.cdc.gov/mmwr/volumes/74/wr/mm7418a2.htm
• The report's figure, from the state health department's analysis, is not reproduced here.