Impacts of urban land cover and anthropogenic heat (AH) on extreme local rainfall over the coastal PRD megacity region during boreal summer are investigated by conducting numerical experiments using the Weather Research and Forecasting (WRF) model coupled with a single-layer urban canopy model (SLUCM). To examine the relative importance of land cover change vs the presence of AH, three numerical experiments corresponding to different levels of urbanization in the PRD area were designed: one with cropland covering the whole region, one with urban land cover but zero AH, and one with urban land cover and a strong diurnal maximum of 300Wm^-2 of AH in the model simulations. Results show that the increase of accumulated rainfall in the urban area is much more sensitive to the intensity of AH than the mere change of surface properties. Urbanization with intense AH can enhance both the intensity and frequency of extreme rainfall, which can be attributed to higher surface temperature (of about 3.5 to 4^oC), higher convective available potential energy (CAPE), and lower convective inhibition (CIN), thus creating an environment more conducive to strong convection over the urban areas. Moreover, enhanced rainfall is supported by moisture supply from the South China Sea and increased water vapor flux convergence over the PRD city area. The amount of moisture flux converging over the coastal megacity area was found to depend on the direction of prevailing background wind.