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Irrigated natural turf measures 4.9°C cooler than baseline average surface temperature

September 29, 2020

Urban heat & materials research

The benefits of living turf have been defined in new research commissioned by Hort Innovation (Conveying the benefits of living turf – mitigation of the urban heat island effect) and prepared by Seed Consulting Services (now Edge Environment).

Land use thermal performance assessment

Based on analysis of landscape-scale thermal data sets in three states (NSW, SA and Victoria), the following key findings are identified:

Across the country, the surface temperature of irrigated natural turf measures 4.9°C cooler than the baseline average surface temperature.

  • In this analysis, long pile synthetic turf is one of the hottest surfaces in the landscape measuring nearly 11°C hotter than average.
  • There is evidence of a difference in the warming potential of synthetic turf with long versus short pile (i.e. the length of the artificial grass blades), with the former having a greater average surface temperature. In contrast, bitumen, which was included as a control, consistently fell between long pile synthetic turf and short pile synthetic turf.
  • On average, non-irrigated natural turf provides a more moderate (1.3°C) but highly variable cooling influence, ranging from 4.4°C cooling in Victoria, to a 1.7°C warming in SA. The thermal performance of non-irrigated living turf depends heavily on the seasonal precipitation during the year of data collection.
  • The analysis of the thermal performance of the five landscape coverings reinforces that natural materials provide a cooling influence compared with built materials that provide a warming influence.

Surface‐to‐air relationship assessment

Field data was collected along transects across six surface types (irrigated living turf, non-irrigated living turf, synthetic turf, bitumen, playing courts and bare ground) during the 2018-19 summer period for air and surface temperature in NSW, SA and Victoria. The following key findings have been identified:

  • When compared with irrigated living turf, natural materials (bare ground and non-irrigated living turf) averaged 10 °C warming over the target surface (between the 1 metre and 4 metre marks), whereas synthetic materials (playing court, bitumen, and synthetic turf) averaged 23°C of warming.
  • At all times during the three hot days of data collection, average surface temperatures over irrigated living turf remained between 34 and 42°C. Temperatures over the target surfaces ranged from 42 to 70°C, with synthetic turf being the hottest measuring between 25 and 33°C hotter than irrigated living turf between the 1 and 4 m marks. Peak temperatures over 70°C for synthetic turf align with observations of the same material recorded in studies by Jim (Jim CY, 2017. Intense summer heat fluxes in artificial turf harm people and environment. Landscape and Urban Planning, Volume 157, pp. 561-576).
  • A key metric explored in the study was the range of influence (RoI), the limit at which the cooling influence of irrigated living turf is no longer measurable. Land surface temperature data collected along each transect provided the strongest example of how temperatures vary with distance from irrigated natural living turf. Universal thermal climate index (UTCI) provided the second strongest signal of the cooling influence of irrigated living turf.
  • Based on scenarios assessed for Sydney, Melbourne and Adelaide, outdoor thermal stress is increased a little (1°C) by the increased surface temperature of synthetic turf, and up to 8°C in cases where a warm surface is sheltered from any prevailing breezes. The results illustrate that for the scenarios analysed, synthetic turf has consistently higher heat stress predicted than irrigated turf.

A report by University of Adelaide, Natural grass vs synthetic surfaces for recreation and sports: an evidence review considers the urban heat and lifecycle costs of living turf versus synthetic turf.

The key take home message is that living green things provide the best urban cooling benefits.

Read the full report here: Conveying the benefits of living turf – mitigation of the urban heat island effect

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