Estimation of urbanization effect on climatic warming over the recent 30 years in Guangzhou, South China

The urbanization effect on climate warming over the recent three decades (1978~2007) in Guangzhou, south China, where has experienced rapid urbanization process since China´s reform and opening-up initiated in the late 1978, was estimated by comparing surface air temperature (SAT) observations in the urban meteorological station with those in its two surrounding rural stations. The climatic warming trend in Guangzhou city is 0.44°C/decade for the urban station and an average of 0.32°C/decade for the rural stations, resulting in an urban warming rate of 0.12°C/decade and a 27.3% contribution proportion to the climatic trend. In addition, there are obvious seasonal changes in the urban heat island intensity and its contribution to urban warming in the climatic change. The largest seasonal urban warming rate due to UHI is in summer and spring with 0.14°C/decade, the second in autumn with 0.11°C/decade, and the smallest in winter being 0.09°C/decade. The largest contribution of urban warming to SAT trend in season is in summer (51.9%), the second in autumn (27.5%), the third in spring (25.9%), and the least in winter (16.4%). Results indicate that urbanization effect could produce different seasonal pattern in UHI intensity variation, enhance the climatic warming rate, and result in overestimating the climatic warming trend to some considerable extent at the local scale. This study can help further improve the understanding of urban climatic change and global warming.