Cooling artificial turf through evaporation from a subsurface water storage unit

The increase in population in cities has led to increased pressure on available sport facilities. As a result, natural grass fields are converted to artificial turf, because fields with artificial turf can be used more frequently. Downsides of these artificial turf fields are the increase in surface temperature and the decrease in infiltration of precipitation resulting in faster discharge. Artificial turf can reach very high surface temperatures leading to unplayable fields and health risks, but also contributing to the urban heat island effect. To counteract these high temperatures, irrigation of the fields is needed, which leads to high water demands. In this study, a system to store precipitation below the fields and to enable evaporation to cool the artificial turf was tested. The system consists of water-storing units below the field, a capillary shockpad that enables water transport to the artificial turf and a natural infill from where water can evaporate. To quantify the effects on temperature and evaporation of the system, four test sites were created with natural grass, conventional artificial turf and two versions of the cooled artificial turf (non-infill and standard). All sites were equipped to measure evaporation, surface temperature, net radiation and water levels below the fields. A separate weather station was installed to measure other meteorological variables (e.g. precipitation, air temperature, wind). During the summer of 2020 on days with a maximum air temperature around 30°C, surface temperature reached 37°C at the cooled standard artificial grass, whereas it reached 62.5°C at the conventional artificial turf. The measured surface temperature for the cooled turf was less than 2°C warmer than the surface temperature at the natural grass site (35.3°C). Evaporation from the cooled artificial turf reached maximum values around 4 mm/d during the summer and was about half of the evaporation from natural grass, whereas evaporation from conventional artificial turf was close to zero. These results show that the system is successful in lowering the surface temperature by evaporation. This reduction in surface temperature is important to maintain playable conditions, but also helps to mitigate the heat island effect. In addition, the water storage below the fields reduces peak discharges during high-intensity precipitation. By combining these functions, the cooled artifical turf fields can help cities adapt to climate change.