Study on the evolution of urban heat island in Tianjin city

s: The Urban Heat Island (UHI) has become more and more serious and affected the ecological environment greatly.The research 0f UHI and its environmental effects is conductive for the city's planning and its suitable development. In this paper, The evolution of UHI in Tianjin city is examined with the temperature data of urban and rural stations (1964—2003) and remote sensing data on June15, 1993 and May 12, 2001. The result shows the development of Tianjin city has obvious effect on UHI. With the rapid development of urbanization, the UHI has intensified at a rate of 0.11 ℃/10a, and the intensity of 2002 reached maximum with a value of 1.2 ℃, which is two times of 1960's. The trend of UHI in July increases obviously. For seasons, the trend of UHI intensity is the largest in autumn (0.16 ℃/ 10a) and the smallest in spring (0.06 ℃/10a). The trends of UHI intensity for maximum temperature difference are generally smaller than those for minimum temperature. The luminance temperature distribution shows the spatial distribution of heat island with some small stronger heat island in it, which is similar to the location of the city. With the development of city, the area of the UHI has been extended. At the end of paper, the mechanisms of UHI's variation are also explored.