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Smartphone apps claim to assess hot weather threats. But are they accurate?

A from the University of Georgia published in GeoHealth found a smartphone application designed to assess heat-related risks frequently reported temperatures that were lower than those recorded through direct on-site measurements.

The app also underestimated the necessity of activity modifications, such as shorter athletic practice schedules, moving physical activities indoors or more frequent water breaks. That could lead to potential safety concerns for athletes, students and other individuals exposed to hot weather conditions.

"Heat is the leading weather killer in the U.S. and among the top three causes of sudden death in sports," said Andrew Grundstein, lead author of the study and a professor in the UGA Franklin College of Arts and Sciences. "Effective environmental monitoring is essential to protecting communities from the growing risks of extreme heat."

Accuracy of smartphone apps is variable

Hot weather poses a significant risk for workers, athletes and military personnel participating in outdoor activities. To prevent heat-related illnesses, athletic programs and school districts, among others, regularly monitor local weather conditions and adjust activity levels and rest breaks accordingly.

They typically rely on onsite measurements of wet bulb globe temperature, which accounts for factors such as air temperature, humidity, wind and sunlight. Recently, smartphone applications have begun offering wet bulb globe temperature (WBGT) estimates as well.

"As more heat tracking tools, such as mobile apps, become available, it's important to assess their accuracy and effectiveness so athletic trainers and other professionals can make informed decisions," Grundstein said. "The big takeaway is that it's a good idea for those who want to use an app for heat safety to understand its accuracy and suitability for a particular location."

The present study suggests onsite WBGT measurements are still the most accurate way to safeguard vulnerable populations—at least for now.

App reported temperatures up to 4° cooler in hot weather

Over two months, the research team gathered data from 26 high schools across 11 U.S. states, measuring WBGT on surfaces such as artificial turf and natural grass.

The results show that while the estimates from the smartphone application were generally similar to the onsite measurements, the app often reported cooler temperatures by up to 4°. The app's accuracy was particularly spotty when WBGT was above 90°, making it less likely to suggest needed activity modifications to keep athletes, students and other vulnerable individuals safe.