Impact Of Urbanization On The Change Of Land Surface Air Temperature Series

Human-induced climate change can be caused by both changed atmospheric composition and land-use through, for example, urban development. The enhanced greenhouse and urban heat island effects both contribute to the warming of the lower troposphere, and many meteorological stations are so close to cities that the warming records are often greatly impacted by the two factors. This is especially true for China which has experienced a rapid and extensive urbanization over the last few decades, therefore, the urban bias should be considered before using the surface historical temperature data. Based on the statistics of 45 cities and the surface air temperature data observed by 45 meteorological stations close to the cities in mainland China, and considering urban size, relative position of meteorological station to city center and winds, this study qualified the degree of the urban impact on observed temperatures at 45 urban or suburban stations and the contributions of urban warming to total warming.The major results are shown as follows:(1) 44 urban stations show a warming trend during 1955-2012 over China excepting Guiyang station, but the magnitudes of warming trend are very different, the minimum and the maximum of annual mean temperature trend are-0.1 °C/10a(Guiyang station) and 0.49 °C/10a(Hohhot).(2) The difference of temperature change among 45 meteorological stations is closely related to the size of urban close to station, relative position of meteorological station to city, the direction and frequency of local prevailing wind. To quantify and represent the impact of urbanization on temperature observed by meteorological station, an index including the three factors mentioned above is proposed, namely Urban impact indicator(Uii). This study found that Uii of 45 stations vary greatly, the range is up to 37% with the minimum of 1%(Yuxi station) and the maximum of 38%(Beijing station).(3) The positive correlation between Uii and annual mean daily temperature of 45 meteorological stations is significant(P<0.05), which indicates that the influences of urbanization on temperature changes observed by 45 stations are significant. Warming caused by urbanization for the annual mean and annual mean minimum temperature of 45 stations are 0.046 °C/10 a and 0.054 °C/10 a, respectively, the contribution of urbanization to the warming of the annual mean and annual mean minimum temperature are 19% and 17%, respectively.(4) As the two adjacent cities, the temperature trends of the stations close to Beijing and Tianjin city are significant different, the seasonal temperature changes observed by the same station are also different, which is as same as the seasonal changes of Uii. The contributions of urbanization to the warming of the annual mean daily minimum temperature of Beijing and Tianjin station are the largest, which are 56% and 100%, respectively.