The impact of urbanization on the monthly averaged diurnal cycle in October 2004 in the Pearl River Delta region

the pearl river delta (prd) region in southern china has experienced rapid urbanization and dramatic economic growth in last 25 years. using identical observed meteorology for lateral boundary conditions, two one-month simulations were conducted: one using the original united states geological survey (usgs) 24-category land cover data (namely nu) and the other using the urban land cover data from 2004 moderate resolution imaging spectroradiometer (modis) satellite images (namely hu) as lower boundary conditions in a mesoscale model. october 2004 was chosen for simulation due to no precipitation in the pearl river delta corresponding to drought conditions. the spatially averaged value (domain-averaged, land-averaged value, urban-averaged value) used for the analysis can reflect the regional climate over an area of several hundreds of kilometers. the simulation results show that the additional urbanization in the prd amplifies the spatially averaged diurnal cycle of surface temperature, sensible heat fluxes and planetary boundary layer (pbl) height, decreases relative humidity, water vapor in the air and latent heat flux, and increases the diurnal temperature range (dtr). the simulation also shows that the urban heat island (uhi) intensity is about 0.4° in the nighttime and about 1.3° in the daytime after the urban expansion.