The cooling effect of irrigation on urban microclimate during heatwave conditions

The emergence of integrated urban water management (IUWM), provides a unique opportunity for passive evaporative cooling of urban environments. This study investigates the potential of purposefully managed irrigation for cooling benefits in a suburb of Adelaide, Australia, where IUWM is widely adopted. SURFEX was used to simulate heatwave conditions across a suburban environment. Results from two simulation periods are presented: model validation period and a heatwave case study. Model validation suggests SURFEX can broadly capture the average intra-suburban diurnal air temperature variability, but not the average maxima and minima. A range of idealised irrigation scenarios were tested with different rates and timing of watering implemented. Clear evidence was found that irrigation reduces air temperature in urban environments. The diurnal average air temperature was reduced by up to 2.3°C. The cooling benefit of increasing irrigation was non-linear, with negligible additional cooling predicted above 20Lm ^-2 d ^-1. The magnitude of cooling was proportional to the pervious (irrigated) fraction, meaning less cooling occurred in areas with greater urban development. Although irrigation increased humidity, it still improved outdoor human thermal comfort during heatwave conditions. IUWM approaches can provide an additional fit-for-purpose water supply to the urban environment, which should be utilised for cooling benefits.