Outdoor sports have become exceptionally warm. Well-known international athletes recently contributed to a report stating extreme heat can pose safety risks during this year's Olympic Games in Paris. Just a month ago, the South American Football Confederation, after FIFA years earlier, officially the rules have changed to take into account “rising temperatures due to climate change.” These heat problems are expected to worsen as temperatures are rising and more communities replace grass with easier to maintain artificial grassAlthough artificial grass is more durable, it has difficulty absorbing and retaining water, ultimately leading to higher surface temperatures. sometimes almost 170 degrees Fahrenheit.
Researchers at the KWR Water Research Institute in the Netherlands sought to tackle these sweltering temperatures on the turf by creating a new, 'evaporative-cooling' artificial material that can collect rainwater and use it to lower temperatures on the surface of a field. The research, published this week in Borders in sustainable cities, found that surface temperatures on their modified turf were 46 degrees cooler than modern artificial grass and nearly the same temperature as natural grass. If this type of self-cooling turf is implemented on a large scale, researchers believe it could reduce the risk of serious heat-related injuries and even help improve stormwater runoff in urban areas, where rainwater is not absorbed well by traditional artificial turf.
“Incorporating underground water storage and capillary irrigation systems into artificial turf pitches can lead to significantly lower surface temperatures compared to conventional artificial turf pitches,” said Marjolein van Huijgevoort, hydrologist at KWR Water Research Institute, in a statement. “With circular on-site water management beneath the pitch, a significant evaporative cooling effect is achieved.”
Evaporated rainwater can make turf almost as cool as natural grass
Natural grass is generally preferable to artificial alternatives in terms of both cooling and drainage, as water can seep into the ground organically. However, sports fields and even a growing number of parks have switched to artificial grass in recent years due to its ease of maintenance. Using the natural water absorption of grass as inspiration, the researchers created their own turf with an open water storage layer placed directly beneath the grass surface and shock absorber. This water layer captures and stores rainwater. Capillary cylinders of hydrophilic stone wool fibers are then used to transport the water back to the surface, where it evaporates. Ultimately, the evaporated water naturally cools the grass surface.
Researchers tested their self-cooling turf against traditional grass and natural grass on a warm, sunny summer day in the Netherlands in 2020. Surface temperatures on their self-cooled track reached 98 degrees Fahrenheit. That’s warm, but nothing compared to the traditional grass, which was a whopping 144 degrees Fahrenheit. What’s more, the self-cooling turf was nearly the same temperature as the natural grass field, which registered 101.6 degrees Fahrenheit.
While other research has previously looked at intermittently cooling artificial turf fields with sprinkler systems, this typically provides only limited, short-term cooling. Constant sprinkling can also damage or impede the playability of the field for sports. KWR researchers say this new approach improves on these efforts by storing naturally occurring rainwater to cool a field when needed. The self-cooling field also reportedly resulted in slightly cooler temperatures above the field surface. In addition to the cooling effects, researchers say the water-absorbing field can also help reduce stormwater runoff, which in turn can combat urban flooding. Poor drainage systems and an abundance of concrete have reportedly contributed to an increase in storm-related flooding during the past years.
Researchers say their new cooling system is relatively simple to implement, but not necessarily cheap. Installation costs for a self-cooling field can be about double that of traditional grass. And while the experiment focused on small 5×5 meter plots of grass, real-world fields could easily exceed that. Still, those initial costs may only tell part of the story. Heat stroke and other health-related or agricultural damage from poor drainage have long-term costs that, in theory, could potentially be mitigated with cooler grass on a larger scale.
“The required investment for a standard refrigerated field is higher than for a conventional field,” the researchers write. “However, this investment ensures that the field becomes part of the on-site water management and provides a cooler and safer field for the athletes, based on natural evaporation of retained (rather than drained) rainwater.”
