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Q&A with Ashley Ward, director of Duke University's Heat Policy Innovation Hub
When does heat go from being uncomfortable to being dangerous for our bodies? North Carolinians have a newly refined, evidence-based system to lean on as they make decisions about outdoor activities and heat precautions.
The NC Department of Health and Human Services introduced the North Carolina Heat Health Alert System in 2018 to send alerts when the heat index reaches thresholds that can cause health issues, particularly for at-risk populations. Last year Duke University's Heat Policy Innovation Hub collaborated with state epidemiologists to update the system with refined regional and seasonal thresholds. Analysis of historical health and meteorological data shows the new system better detected harmful heat events early and late in heat season.
Hub Director Ashley Ward was part of the team that updated the system. Ward explains the recent improvements to the system and the potential for further refinements.
Ashley Ward, Ph.D., Heat Policy Innovation Hub Director
What makes North Carolina’s heat alert system unique compared to other states?
North Carolina’s system is important because it connects weather conditions to actual health outcomes. Many heat alert systems are based primarily on meteorological thresholds, such as how rare the high temperatures are compared to historic data. North Carolina has gone a step further by incorporating not only meteorological data but data that shows when people show up in the emergency departments.
North Carolina’s syndromic surveillance system, NCDETECT, is maintained by the NC Department of Health and Human Services and provides real-time emergency department data. This allows us to evaluate which temperature thresholds result in health outcomes across different regions in North Carolina. For example, people who live in the coastal plain may have a different trigger than those who live in the mountains.
This kind of outcome-based regional, statewide alert system is one of very few in the nation.
The revamped system divides North Carolina into eight distinct climatological regions. Why is it important to have different thresholds for each of these regions?
Heat does not impact every part of North Carolina in the same way. The mountains, Piedmont, Sandhills, coastal plain and coast experience heat and humidity differently, and communities in those regions may have different patterns of exposure, different kinds of housing, work and baseline risk.
A single, statewide threshold can miss those differences. Regional thresholds allow the state to issue alerts that better reflect when heat is likely to become dangerous for people where they live and work.
The 2025 update also introduced seasonal thresholds to the system. How does the human body’s response to heat change across those seasons?
The timing of heat matters. A 95-degree heat index in May can affect people differently than the same heat index in August. This is because our bodies and behaviors change over the course of the season.
Early-season heat can especially be risky because people may not yet be acclimatized, schools and employers may not have shifted routines and households may not yet be prepared for sustained cooling needs.
Seasonal thresholds help the alert system recognize that dangerous heat is not only about the number on the thermometer; it is also about when on the calendar heat occurs.
How could the system be strengthened even further?
The next major opportunity is delivery. Email alerts are valuable, especially for agencies, local governments, health departments and community organizations that help push information out to the public. These are trusted community voices that can substantively reduce heat burdens simply by passing along warnings. But the people at greatest risk may not be checking email at the right moment, or they may need a simpler, faster message. As Duke University School of Medicine researchers Hayden Bosworth and Elizabeth Rojo noted in a recent journal article, text alerts could make the system even more actionable.
I'd argue that stronger integration with trusted community messengers and tailored guidance for outdoor workers, older adults, caregivers, schools and people without reliable cooling would also be helpful.
Another opportunity I see is to incorporate nighttime heat more directly into the heat alert system. Hot nights are a major driver of health risk because they prevent the body from recovering after daytime heat exposure. That risk depends not only on outdoor temperatures, but also on whether people can safely and affordably cool their homes overnight. Nighttime heat can become especially dangerous in places with unreliable electricity, high energy costs, older housing or limited access to air conditioning.
For media inquiries, contact the Nicholas Institute communications team at ni-comm@duke.edu.
