Abstract
The urban heat island phenomenon occurs as a mixed result of anthropogenic heat discharge, decreased vegetation, and increased artificial impervious surfaces. To clarify the contribution of each factor to the urban heat island, it is necessary to evaluate the surface heat balance. Satellite remote sensing data of Tainan City, Taiwan, obtained from Terra ASTER and Formosat-2 were used to estimate surface heat balance in this study. ASTER data is suitable for analyzing heat balance because of the wide spectral range. We used Formosat-2 multispectral data to classify the land surface, which was used to interpolate some surface parameters for estimating heat fluxes. Because of the high spatial resolution of the Formosat-2 image, more roads, open spaces and small vegetation areas could be distinguished from buildings in urban areas; however, misclassifications of land cover in such areas using ASTER data would overestimate the sensible heat flux. On the other hand, the small vegetated areas detected from the Formosat-2 image slightly increased the estimation of latent heat flux. As a result, the storage heat flux derived from Formosat-2 is higher than that derived from ASTER data in most areas. From these results, we can conclude that the higher resolution land coverage map increases accuracy of the heat balance analysis. Storage heat flux occupies about 60 to 80% of the net radiation in most of the artificial surface areas in spite of their usages. Because of the homogeneity of the building roof materials, there is no contrast between the storage heat flux in business and residential areas. In sparsely vegetated urban areas, more heat is stored and latent heat is smaller than that in the forested suburbs. This result implies that density of vegetation has a significant influence in decreasing temperatures.
Highlights
The urban heat island effect is the temperature increase according to urbanization and has been studied for about four decades
This paper presents a case study of surface heat balance that was estimated based on surface classification maps from ASTER and Formosat-2 data in Tainan City, Taiwan on March 6, 2001
In order to individually assess the effects by the roughness length and the stomatal resistance to heat flux estimation, we estimated heat fluxes according to the following two cases: 1) heat fluxes estimated based on the roughness length from Formosat-2 and the minimum stomatal resistance from ASTER, and 2) heat fluxes estimated based on the roughness length from ASTER and the minimum stomatal resistance from Formosat-2, respectively
Summary
The urban heat island effect is the temperature increase according to urbanization and has been studied for about four decades. The urban heat island phenomenon occurs as a mixed result of anthropogenic heat discharge, decreased vegetation cover, and increased use of artificial impervious surface materials. These factors modify the heat balance at the land surface and eventually raise the atmospheric temperature. The same authors [2] introduced storage heat flux, ∆G, in order to evaluate the heat storage and discharge of urban surfaces Their results of estimated heat fluxes are reasonable compared with previous ground measurement data in other cities [3,4,5,6,7,8].
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