Identifying the mechanisms by which irrigation can cool urban green spaces in summer.

High temperatures in summer can prevent people from using urban green spaces. Irrigating urban green spaces is a promising strategy to reduce temperatures. In this study, we aimed to a) identify the proportional contribution of different irrigation cooling mechanisms and b) quantify the impacts of different irrigation amounts (from 2 to 30 mm d⁻¹) on the cooling effect of irrigating turfgrass in Melbourne, Australia. We first used a field experiment in Melbourne to provide empirical data to calibrate and verify the performance of an urban ecohydrological model, UT&C. Then, we used UT&C to predict the impacts of irrigating turfgrass on evapotranspiration, the energy balance and microclimate. UT&C predicted that irrigating turfgrass 4 mm d⁻¹ would increase the evaporation from grass canopy and soil surface by 0.2 and 0.6 mm d⁻¹, respectively, whereas it would reduce transpiration by 0.6 mm d⁻¹ due to intercepted water covering part of the grass canopy following the irrigation. UT&C predicted that daytime (10:00–16:59) mean air temperature reductions would increase from 0.2 to 0.4 °C when the irrigation amount increased from 2 to 4 mm d⁻¹. However, increasing the irrigation amount beyond 4 mm d⁻¹ would not increase the cooling benefits. [Display omitted] • We measured the cooling effects of irrigating urban green spaces. • We used a model to identify cooling mechanisms and optimal ideal irrigation amount. • Irrigating grass increased evaporation from soil surface and canopy interception. • Increasing irrigation amount beyond 4 mm d⁻¹ would not strengthen cooling effect. • Irrigating grass 4 mm d⁻¹ significantly reduced daytime air temperature by 0.4 °C. [ABSTRACT FROM AUTHOR]