Estimation of heat storage and discharge from in the urban area using ASTER data
The urban heat-island phenomenon occurs as a result of mixed effects by anthropogenic heat discharge, increase of artificial impervious surface materials, and decrease of vegetation cover. These causes modify the heat balance at land surface, and eventually raise atmospheric temperature.
In this study, instantaneous surface heat fluxes were estimated around the city of Nagoya, Japan using Terra ASTER data products along with the meteorological data provided by Japan Meteorological Agency. In order to compare seasonal and day-night differences, ASTER data acquired in the daytime on July 10, 2000, and January 2, 2004 and nighttime on September 26, 2003 were used.
Surface heat fluxes were estimated based on the theoretical heat balance equation. Because it was difficult to know the ground heat flux and anthropogenic heat discharge, the net heat flux combining these two components was inferred as a residual of the net radiation, sensible heat, and latent heat fluxes in the heat balance equation. When an upward heat exists, it was defined as the heat discharge, while in the opposite case, it was interpreted as the heat storage.
As a result, heat discharge appeared mainly in the industrial areas for both daytime of summer and winter, and nighttime of autumn. In the central business and commercial districts, the heat storage was higher than those in the surrounding residential areas. Particularly in winter, the heat storage in the central urban area was 220 to 280 Wm-2, and was much larger than those in the residential areas, 150 to 200 Wm-2. Moreover the heat discharge in the central urban area was relatively higher in nighttime. This tendency implies that the large heat capacity of buildings provides high heat storage during daytime in the central urban area, and contributes to temperature rise as a result of the heat discharge in nighttime.