Is the urban heat island exacerbated during heatwaves in southern Australian cities?

The extra-tropical Australian cities of Melbourne, Adelaide, and Perth are all affected by summer heatwaves and the urban heat island (UHI) effect. While research has been undertaken on both phenomena individually, they have not been studied in tandem in Australia. This research investigates the relationship between warm season heatwaves (November to March) and the UHI from January 1995 to March 2014. Observational temperature data from six or seven Bureau of Meteorology Automatic Weather Stations in each of Melbourne, Adelaide, and Perth are used to determine the strength of the UHI during heatwave periods and these are compared to non-heatwave periods. Melbourne and Adelaide both experience an exacerbated (warmer than normal) UHI at night during heatwaves. The night-time UHI in Perth is diminished (cooler than normal) during heatwaves and often changes to an urban cool island (UCI), when compared to non-heatwave periods. Environmental factors that might affect the strength of the UHI are investigated, including wind speed and direction, and station location. Despite the proximity of all stations to the coast, coastal influences on UHI strength are minimal during heatwave conditions. Station choice is found to not affect our results, with the characteristic pattern of the UHI during heatwaves remaining consistent across all three cities in a leave-one-out sensitivity analysis.