On the cooling potential of irrigation to mitigate urban heat island.

Urban overheating is the most documented phenomenon of climate change, causing severe energy problems. The study aims to evaluate the mitigation potential of irrigation as a response to the urban overheating and heatwaves in large cities, using simulation-based techniques. Mesoscale simulations are conducted for a 32.5 km × 22.5 km metropolitan region of Sydney, Australia, and it is modelled based on the moderate resolution imaging spectroradiometer (MODIS) 500 m resolution land surface dataset. To better represent the Sydney metropolitan area, the New South Wales Land Zoning dataset is used to remap the land surface. The weather research forecast model (WRF) combined with the urban canopy model (UCM) is used as the simulation tool. The results show that a daily irrigation scheme results in a maximum daily temperature drop of approximately 1.3 °C and an average daily air temperature decrease close to 0.5 °C. It is also found that the cooling effect due to the additional irrigation is strongly correlated to the ambient temperature, urban fraction, and the soil moisture state before irrigation. The irrigation induced cooling effect tends to be higher in the urban areas where the soil is drier before irrigation, or in a larger portion of the area that is covered with vegetation, or where the ambient temperature is higher.