Response of urban heat islands to heat waves in the Guangdong-Hong Kong-Macao Greater Bay Area

The synergistic interactions between urban heat islands (UHI) and heat waves remains relatively understudied in the Guangdong-Hong Kong-Macao Greater Bay Area, a region undergoing rapid urbanisation. This study explores this issue by analysing three typical heat waves using the coupled Weather Research and Forecasting (WRF) / Multilayer Urban Canopy and Building Energy Model (BEP/BEM). It is found that heatwaves significantly amplified the nighttime UHI, with an average increase of more than 1 °C, especially affecting areas that were already characterised by strong UHI during non-heatwave periods, where the maximum increase in UHI was 3 °C during the heat waves. In contrast the heat waves had little effect on the daytime UHI, which did not pass the 95% significance test in most areas. Using a biophysical factorization method, heat waves-induced temperature changes were attributed to different driving factors. Results suggested that the enhancement of nighttime UHI during heat waveswas associated mainly with greater anthropogenic heat, storage heat and enhanced warm advection. Comparing storage heat and anthropogenic heat, the former played a more important role in the early morning as opposed to anthropogenic heat, which contributed more in the evening.