“Self-cooling” artificial grass field to refresh cities

Posted on 01 June 2021.

Could areas of artificial turf have a natural cooling effect? This solution, tested in the Netherlands as part of the CitySports project, contributes to both the reduction of urban heat islands and to sustainable rainwater management.

“On sunny days, the water stored beneath the pitch will evaporate, naturally cooling the site and the surrounding area and helping to cool the city.”

Established in 2012 by the Dutch Ministry of Economic Affairs and Climate Policy, the Top Consortia for Knowledge and Innovation (TKIs) are programmes in which entrepreneurs and researchers work together to develop innovative solutions in key sectors of the economy.

TKI project CitySports is part of the Water and Maritime Affairs consortium. Launched in 2018, it aims to design and test a safer, more sustainable and more comfortable alternative for athletes to conventional artificial turf sports fields, which are the subject of widespread criticism.

The Dutch Watercycle Research Institute (KWR), in close cooperation with the City of Amsterdam, Waternet, DutchBlue, Drain Products Europe and Veolia, has tested several samples of artificial grass field systems at the Marineterrein Living Lab in Amsterdam. Based on these results, the most effective system has been installed at football club VVA Spartaan in the City of Amsterdam.


The urban heat island phenomenon

There are many concerns about the use of large quantities of rubber powder, derived from the recycling of waste tyres, for infilling artificial grass. This material could have adverse effects on human health and the environment due to the possible release of toxic compounds (such as lead) into the air and also into drained water.

In addition, artificial turf suffers from the major disadvantage that it heats up in the sun to a greater extent and much more quickly than natural turf. In the summer, some sites have reached temperatures of 60°C, making them totally unusable! This overheating phenomenon contributes to the urban heat island effect, a kind of microclimate in which the temperature is significantly higher than elsewhere in the same region or even the same city.

Several years ago, a researcher at the Centre for the Study of Climate Systems at Columbia University in New York discovered, by analysing satellite images of the “Big Apple”, that many of the heat bubbles present were in fact sports fields.

This phenomenon also exists in Amsterdam, which features around 100 artificial turf pitches and has experienced several heat waves. It was specifically to help the city cope with increasingly frequent heat waves that the CitySports pilot project was launched.


Refreshing the city rather than heating it up

The artificial turf system tested by KWR consists of a subbase made of water storage units, where rainwater is collected and stored before being used. These units, made from recycled materials by Veolia, contain very thin tubes that will naturally transport water by capillary action to the cushioning layer and then to the synthetic grass surface. On sunny days, the water will evaporate, naturally cooling the site and the surrounding area without the need for watering and thus helping to cool the city.

In addition to significantly reducing the contribution of artificial pitches to the urban heat island phenomenon, this passive cooling system will thus provide a further instrument for (sustainable!) rainwater management.

During the spring of 2020, KWR collected data from the sensors installed at all the test sites. The results are impressive: during the afternoon of 25 June, in the middle of one of the hottest periods of the year, the surface temperature of the conventional artificial turf was 62.2°C. The surface temperature of the "self-cooling" artificial turf was 35.9°C, only 1°C higher than natural grass.