An urban heat island indicates an area with relatively warm surface, and most commonly the areas of human disturbance such as towns and cities. The cause of such a phenomenon is distributed in two major components. One factor is the change of land cover. Vegetation and water area that play important roles in alleviating the rise of air temperature are decreasing, and artificial land covers that have high heat capacity like asphalt and concrete are increasing. Another factor is the increase of artificial heat emission. Especially the emission from automobile and artificial cooling has been increasing recently. Now, there are lots of studies dealing with these topics, but the studies from the viewpoint of quantity are not enough. In this research the urban heat islands of Tehran, as the most important population center and one of the most important industrial center of Iran, is investigated.
The aim of this work is investigating the relationship between land cover proportions and UHI with ETM+ images of Tehran. To achieve this, for mapping land surface materials with distinct physical properties from Landsat ETM+, the linear spectral unmixing method was utilized for endmember fraction estimation. The transformed ETM+ image was unmixed into four fraction images (vegetation, soil, high albedo and low albedo). Impervious surfaces were then computed from the high and low albedo images. Multiple regression models were further developed to reveal how land surface temperatures were related to urban biophysical descriptors (i.e., impervious surfaces, green vegetation, and soil). Results indicate that impervious surfaces, because of high heat capacity and anthropogenic heat emissions into the air and dry soil through high heat capacity, were positively correlated; while vegetation was negatively correlated with land surface temperater. Also industrial area has the most positively correlated with land surface temperature, because the anthropogenic heat flux in industrial areas is high.
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