Direct Effects on Temperature Rise by Anthropogenic Heat Emissionsinto the Metropolitan Urban Atmosphere

The so-called heat island phenomena found over large urban areas are thought to arise due to many causes; one of the major causes of the phenomena is direct heating of the lower atmospheric boundary layer by anthropogenic heat emissions. However, no quantitative assessment of this cause has been reported. Recently developed numerical regional meteorological modeling techniques enable us to estimate the temperature rise resulting from anthropogenic heat emissions into the atmosphere. However, it remains difficult both to perform more than a single-year integration with these numerical meteorological models and to evaluate the annual mean temperature rise resulting from anthropogenic heat.Using a simplified analytical atmospheric dispersion model we estimated the annual mean air temperature rise in the surface layer due to direct heating by anthropogenic heat emissions in to the urban atmosphere over the Tokyo metropolitan area. The validity of this model was verified by applying it to the dispersion of nitrogen oxides over the same area. The temperature rise at the center of Tokyo resulting from anthropogenic heat emissions was estimated to be about 0.7 to 1.1°C. On the other hand, observations from our densely distributed, long-term monitoring network in this area showed that the annual mean temperature at the center of Tokyo was about 2.6 °C higher than the surrounding rural areas. We conclude that direct heating by anthropogenic heat sources accounts for 27% to 42% of the annual average observed heat-island intensity in the Tokyo metropolitan area.