When managing athlete safety during hot weather, many people wonder whether the type of surface—be it grass, turf, or track—affects Wet Bulb Globe Temperature (WBGT) readings. After all, anyone who’s stood on a turf field on a sunny day knows it can feel significantly hotter underfoot compared to a grassy area.
But does that mean you need to monitor WBGT or Heat Index readings separately for each surface? The answer, according to experts, might surprise you. A recent study provides evidence that WBGT is consistent over different athletic surfaces.
“In the nerdy weather world that I live in,” says Colin Perry, meteorologist and CEO at Perry Weather, “there’s a couple of what I call the godfathers of heat stress monitoring, and Dr. Grundstein and his team over at the University of Georgia have spent most of their career studying these types of effects of heat stress on athletes.” Dr. Grundstein and his team of researchers at the University of Georgia compared WBGT values over grass, artificial turf, and tennis courts at their athletic facility. They found no statistically significant differences in the WBGT measurements over these varied surfaces.
This suggests centralized WBGT monitoring from one sensor can be reasonably representative for nearby athletic fields, at least in certain conditions.
WBGT combines air temperature, humidity, wind speed, and radiant heat into a single value representing heat stress. It is measured using a thermometer with a wet bulb, a black globe, and a dry bulb.
Surface type doesn’t directly impact WBGT because it is mainly a factor in radiant heat absorption. But radiant heat is just one component balanced with air temperature and humidity. As long as moisture levels are sufficient, the evaporative cooling effect dominates over radiant heat from the surface.
Dr. Andrew Grundstein‘s study at the University of Georgia athletic complex had adjacent fields with grass, artificial turf, and hardcourt tennis surfaces. WBGT measurements were collected simultaneously from sensors positioned 1.25 meters above each surface. Data was gathered every 10 minutes from 9am to 6pm over 4 days in July 2019.
The researchers analyzed differences in WBGT as well as its component measurements across the three athletic surfaces.
The key finding was that WBGT measurements were statistically similar over grass, artificial turf, and tennis courts. This consistency held even when comparing morning, midday, and afternoon time periods.
On average, the grass field had a WBGT of 82.4°F, while the artificial turf and tennis courts measured 82.9°F and 83.1°F respectively. The maximum difference was only 0.7°F.
According to the study, “The lack of difference in WBGT among the surfaces is due to the counterbalancing influences of the different components in the WBGT index.” This suggests WBGT can be monitored from a single location at this athletic complex without compromising accuracy.
That’s not to say there’s no difference at all. For example, synthetic turf might register slightly higher temperatures but lower humidity because it drains moisture efficiently. On the other hand, grass might show a slightly lower temperature but higher humidity due to its ability to retain moisture. However, these variations are small and tend to balance each other out.
The key takeaway here is that while a turf field might feel much hotter to the touch than a grass field, this difference doesn’t translate into a significant change in WBGT readings at the standard measurement height. The air above these surfaces mixes and averages out the heat differences, making the impact of the surface type minimal when it comes to WBGT. This study provides evidence that monitoring WBGT from one location can sufficiently represent the entire athletic complex, at least in humid climates over well-watered grass. As Colin Perry explains, “Although the surface itself might feel hotter when you touch it, when the WBGT is measured at about head height, the air actually mixes up very well and so it has a very negligible impact.”
Since the WBGT differences were minor, adopting more extensive monitoring across multiple fields may provide limited additional value. A single WBGT sensor placed in a representative central location can be reasonable to implement heat safety guidelines. However, it is important to note that the study was limited to a single athletic facility. Further research across different climates, irrigation practices, and surface materials would build greater confidence in applying centralized WBGT monitoring.
Monitoring fewer locations reduces costs and complexity. But organizations should weigh this against any risks and liabilities if localized hotspots go undetected. A layered approach combining centralized monitoring and vigilance during practices may offer prudent heat safety.
For those in charge of monitoring WBGT or Heat Index readings on campuses with a variety of surfaces, this is good news. You don’t need to run around taking separate measurements on every type of surface. As Colin puts it, “If I’m an athletic trainer or if I’m the one responsible for monitoring heat, heat index, and WBGT, I do not have to go around to every single surface and take measurements of all of these all day long. I’m good if I just do it on one surface within a one square mile or five square miles around my campus.”
This simplifies the process significantly. Instead of juggling multiple devices and readings, you can focus on accurate, consistent monitoring from a single location, confident that the differences across various surfaces are negligible.
So, what’s the bottom line? The surface type—whether it’s grass, turf, or track—has little impact on WBGT readings when measured correctly. The differences in temperature and humidity balance out at the standard measurement height, so a single WBGT reading from one surface is sufficient for ensuring athlete safety across different fields or courts.
This study found wet bulb globe temperatures were statistically similar over grass, artificial turf, and tennis courts at a university athletic complex. Minor microclimate variations in temperature and humidity largely counterbalanced when incorporated into WBGT. Centralized WBGT monitoring provided reasonably representative values across the athletic surfaces.
Research at the University of Georgia found that wet bulb globe temperature (WBGT) measurements were statistically the same over adjacent grass, artificial turf, and tennis court surfaces. WBGT incorporates air temperature, humidity, wind, and radiant heat into a single value. Surface type doesn’t directly impact the WBGT.
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