Abstract: This paper quantitatively analyzed the effects of urban expansion on city thermal environment, taking the urban area of Lanzhou City as a case, and based on the 1978, 1993, 2001 and 2010 Landsat/TM and ETM⁺ images. The information of urban construction land was extracted by using NDBI-NDVI index, and the land surface temperature was retrieved via mono-window algorithm, with the urban heat-island ratio index and the land surface temperature grade maps built. In 1978-2010, the construction land in the central area of Lanzhou City increased from 87.47 km² to 172.61 km², and the urban expansion had a spatial consistency with the urban heat island expansion. At the same time of urban expansion, the urban surface temperature increased gradually, and the heat island area had an increasing expansion.

Key words: Polytrichum juniperinum, History reconstruction, Population dynamics