Large seasonal and diurnal anthropogenic heat flux across four Australian cities

Anthropogenic heat release is a key component of the urban heat island. However, it is often excluded from studies of the urban heat island because reliable estimates are not available. This omission is important because anthropogenic heat can contribute up to 4ºC to the urban heat island, and increases heat stress to urban residents. The exclusion of anthropogenic heat means the urban heat island effect on temperatures may be under-estimated. Here we estimate anthropogenic heat for four Australian capital cities (Brisbane, Sydney, Melbourne and Adelaide) to inform the management of the urban heat island in a changing climate. Anthropogenic heat release was calculated using 2011 population census data and an inventory of hourly traffic volume, building electricity and gas use. Melbourne had the highest annual daily average anthropogenic heat emissions, which reached 376 W/m² in the city centre during the daytime, while Brisbane’s emissions were 261 W/m² and Sydney’s were 256 W/m² . Adelaide had the lowest emissions, with a daily average of 39 W/m² in the city centre. Emissions varied within and among the four cities and decreased rapidly with distance from the city centre, to < 5 W/m² at 20 km from the city in Brisbane, and 15 km in Adelaide. The highest emissions were found in the city centres during working hours. The peak emissions reached in the centre of Melbourne are similar to the peak emissions in London and Tokyo, where anthropogenic heat is a large component of the urban heat island. This indicates that anthropogenic heat could be an important contributor to the urban heat island in Australian capital cities, and needs to be considered in climate adaptation studies. This is an important problem because climate change, combined with an ageing population and urban growth, could double the deaths from heatwaves in Australian cities over the next 40 years.