Study on the evolution tendency of the urban heat island effect in Xichang City using Remote Sensing

Using Landsat TM/ETM+ images acquired on July 31, 1995, August 27, 2002, and September 18, 2007, the brightness temperature was retrieved. Built-up areas were extracted from images by combining normalized difference building index (NDBI), supervised classification, and unsupervised classification method. Meanwhile, their temperature was calculated. The heat island intensity of built-up area in Xichang City was calculated; simultaneously, the city thermal environment evolution trend was analyzed by using the urban heat island ratio index. The results show that: (1) Chronologically according to the images, the built-up area were 12.2 hm², 20.35 hm² and 23.79 hm² respectively, and the heat island intensity were 3.375 °C, 3.445 °C, and 3.606, °C respectively; (2) Before 2002, the built-up area expansion rate was 1.164 hm²/a, and the increase rate of heat island intensity was 0.010°C/a. After 2002, they were 0.688 hm²/a and 0.032°C/a respectively. (3) the heat island ratio index in study area were 0.869, 0.933, and 0.955, respectively. The Urban Heat Island Effects showed an overall upward trend.