RS based study on urban expansion and its impact on city heat island effect in Chuxiong City in Yunnan, China

Based on the building areas information extracted from the multi-temporal Landsat data, city boundaries (measured by GPS on November 2008), land surface temperature (retrieved from band 6 of Landsat TM5 images) and year-book data, this paper discusses the urban expansion characteristics and their impact on the city heat island effect in Chuxiong City over the past 30 years. The urban expansion of Chuxiong City over the past 30 years could be divided into three periods: the slow development period from 1979 to 1991, the accelerated development period from 1992 to 2003 and the rapid development period from 2004 to 2008. In the past 30 years, the center of the city moved northward. The annual average expansion area increased from 0.4 km² to l.21 km², and the urban expansion and population rise flexibility index increased from 0.86 to 1.56 gradually. The built-up area has increased by 7 times, mainly by occupying the farmland and garden. Urban expansion has had a great effect on heat island effect in the past 30 years. The heat island effect hardly occurred before the 1980s. But in 1989, the temperature of urban areas was 0.5degC higher than that of suburbs, 1.1degC in 1999 and 1.35degC in 2007. The temperature of new town was 0.7degC higher than that of old town in 1999 and 0.1? in 2007. The hot island intensity in urban areas has increased, the temperature difference between new town and old town has reduced and the temperature of old town has also gradually increased in the past 30 years. At the same time, the distribution of city high-temperature zone has extended to the west of old town and industrial areas, and was significantly affected by human activities, topography and industry development. The distribution of low-temperature zone has changed from sporadic area to Longchuan River zone.