わが国における都市ヒートアイラント形成要因, とくに都市ヒートアイランド強度形成要因に関する研究の動向

概要

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Fujibe (2007) reviewed urban climate research in Japan, and presented five formation factors of the urban heat island: (1) anthropogenic heat, (2) decreased evapotranspiration due to urbanization (especially removal of vegetation), (3) change of heat balance equation for urban canopy, (4) greenhouse effect due to air pollution, and (5) dynamic mixing due to buildings. Fujibe (2007) assumes the latter two formation factors of the urban heat island (4) and (5) are not determinate, although he concluded that the former three formation factors from (1) to (3) are correct. Although Fujibes (2007) review is excellent, the above-mentioned factors were already described clearly in Okes (1978) textbook, and are described from a viewpoint that is biased towards changes in the urban surface heat balance. The above factor (5), dynamic mixing due to buildings, is not a change in the urban surface heat balance, but considers changes in the thermal capacity of the urban boundary layer. The present paper reviews studies on the formation mechanism of the urban heat island in Japan with special emphasis on the relationships between heat island intensity and boundary layer of urban areas. As a result, it is pointed out that the different wind velocity dependency of the urban heat island intensity responds to the fact that the urban boundary layer is divided into the urban dome under calm conditions and the urban plume under windy conditions.
2011-04-25