Heat balance analysis in Taiwanese cities using aster and formosat-2 data

Abstract

In order to compare the influences of urbanization to urban heat island in different cities, surface heat balances on three urban areas in Taiwan, namely Kaohsiung City, Taichung City, and Tainan City, were estimated from remote sensing and ground meteorological data. We estimated heat fluxes by using ASTER data with surface classification map by Formosat-2. Because the orbit of ASTER and positions of the three cities are almost parallel, we could compare the surface heat balances of the study areas for the same day. The surface heat balance of each city shows obvious differences according to their characteristics of city scale, usage, and geographic conditions. The net radiation ranges showed similar values in all of the study areas because the three cities are located close to each other and the net radiation is primarily due to solar radiation. On the other hand, in Tainan City, which is the smallest in the three cities, sensible heat flux was 60 to 70 % of those in Taichung City and Kaohsiung City. Moreover, Taichung City, located in a basin, shows relatively larger sensible heat flux than Kaohsiung City caused by a temperature decrease during the night before the observation. Storage heat flux clearly shows the influence of anthropogenic heat discharge in some industrial areas in Kaohsiung City and Taichung City. Meanwhile, smaller urban function induces moderate distribution of storage heat flux in Tainan City. These results imply that the terrain around the certain city also affects the heat balance significantly as well as artificial influence.