Comparison of Energy Balance between Rooftop Surface in Urban Area and Grass Plot Surface in Suburban Area

Heat balance and radiation balance at the rooftop surface in urban area and the grass plot surface in suburban area of Hiroshima City were estimated on the basis of observation data in summer and winter. Difference in diurnal variation of energy balance between the rooftop surface and the grass plot surface was described preliminarily in this paper. As to the heat flux from the rooftop surface to the atmosphere, though the sensible heat flux is much larger than the latent heat flux in the afternoon, the latent heat flux is larger than the sensible heat flux in the morning. Therefore, the latent heat flux from the rooftop surface can not be disregarded. The sensible heat flux from the rooftop surface is larger than that from the grass plot surface during the daytime, which could cause higher temperature above the rooftop. Moreover, the heat flux into (daytime) / from (night) the inside of the building is larger than that into / from the soil of the grass plot especially in summer. This means that the heat storage of building is important for the energy balance of urban area in summer rather than in winter. Nighttime radiation cooling from the rooftop surface is stronger than that from the grass plot surface