Urban anthropogenic heat is emitted from transportation, manufacturing, industry, houses, offices and energy sectors. None of them are easy to estimate or measure, resulting in the obscure contribution of each heat source to the urban atmosphere. In addition, the amount and distribution of each source in the future is much more difficult to quantify due to the uncertainty arises from the technological improvement of energy efficiency, economic development and the energy law enforcement.

In this paper, spatial and temporal distributions of anthropogenic heat emission from buildings and vehicles are quantified over the Kanto plain that covers major metropolitan cities including Tokyo metropolitan area, based on the available data sources. The data include the type and floor area of buildings, household numbers, and the volume and type of traffic, etc. The amount of anthropogenic heat emissions and patterns of diurnal and seasonal variations are parameterized in relation to the land use type. It is found that the anthropogenic emission from transportation is comparable to that from buildings for household and business purposes, especially in suburban areas. Future potential increase of those emissions is estimated by assuming future situation associated with the energy use, referring to reports from the government and municipal authorities.

Various countermeasures are searched for to reduce anthropogenic heat emission from vehicles and buildings. Traffic demand control, lighter vehicle and introducing fuel cells are the measures concerned with automobile emission reduction. Heat reduction is also expected for the decrease in domestic and commercial energy use by introducing energy-efficient electrical devices, achieving high insulation of buildings, high individual consciousness of the effective energy use, district heating and cooling in combination with water heat pump system. The amount of heat reduction in each measure is integrated to estimate the total amount of anthropogenic heat reduction over the Kanto plain in the near future.

In this study, a mesoscale model based on the PSU/MM5 was applied to the Kanto plain to see the impact of reduced anthropogenic heat. This model is characterized by some features added to the original MM5 such as the parameterization of surface heterogeneity to deal with complex urban land-use, inclusion of a land surface model, and the anthropogenic heat emission with spatial and temporal variation.

The base-case simulation was carried out for 3 days in summer, 1995 under clear sky conditions, showing fairly good agreements with observed air temperature at many urban and suburban locations. Then the model was used to estimate the changes in air temperature, humidity and wind field, giving spatial and temporal distribution of anthropogenic heat emission in the future. The impact of anthropogenic heat from vehicles is larger than that from buildings in the morning and night. The integrated impact of reducing anthropogenic heat is large over the inland region in the night, whereas the impact in the central Tokyo area is not so large compared to other possible mitigation measures such as introducing green roof, enlarging urban water surface and installing cool pavement.