With rapid growth of economy and expansion of cities, urbanization has become a significant factor in affecting the long-term changes of mean and extreme temperature and other key climatic variablesat most urban stations of mainland China. So far, this problem has aroused more and more attentions in urbanization effect on mean temperature trends, but the few analysis of urbanization effect on temperature probability density distribution has been done. This article analyzes the urbanization effect on daily temperature probability density distribution(PDF), daily temperature cumulative probability density distribution (CDF) and the seasonal cycles of daily mean temperature for Shijiazhuang weather station without any relocation before 2011 as an example. This paper uses daily data of T-mean, T-min, and T-max of an urban weather station, Shijiazhuang station, and a nearby rural weather station, Gaocheng station, from 1962 to 2011. Shijiazhuang station was never moved before 2011. Urbanization effect (Delta T-ur) is defined as the temperature trends or change in daily temperature PDF and CDF of urban station caused by the changing Urban Heat Island (UHI) intensity and/or the effect of other factors (such as aerosols). The urbanization makes the distribution of annual T-mean, T-min, and T-max at Shijiazhuang station during 1962-2011 shift to high temperature side. Urbanization effect on the distribution of annual T-min, is very obvious, but the effect on the distribution of annual T-max is small. Due to the urbanization effect, the increase in T-min is larger on high value side than on low value side at Shijiazhuang station, resulting in a flatter shape of annual T-min PDF than that of the rural station; The PDF of T-mean, T-min, and T-max at Shijiazhuang station all shifts to the higher value side during 1987-2011 compared to 1962-1986, with the largest shift occurring in T-min The PDF of T-min at Shijiazhuang station in the time period 1962-2011 is characterized by a non-normal distribution due to the urbanization effect. The difference of PDF between Shijiazhuang station and Gaocheng station during 1962-2011 is larger and more significant in winter and spring than in summer and autumn, and the largest difference is found for winter T-min. The urbanization effect in the 1962- 2011 series of cold nights and warm nights are respectively -1. 13 d/10a and 1.48 d/10a, and the urbanization contribution are respectively 28. 32% and 37. 76%. The urbanization effects in the T-min-based extreme temperature indicesare larger for those in the T-max-based extreme temperature indices at Shijiazhuang station. In each of the seasons of a year, the daily mean T-min, difference between the urban and rural stations is generally more than 1.0 degrees C, with the daily urban heat island intensity, sometimes reaching above 1.5 degrees C, being the largest from the beginning of December to the end of May, and the daily mean T-max difference between the urban and rural stations is usually less than 0.5 degrees C. The significant urbanization effect on urban station surface air temperature records exists not merely in the linear trends of mean temperature series and extreme temperature indices series, but also in the probability density distribution of daily T-min, and T-max It is an important factor in forming the asymmetry changes of diurnal and seasonal temperature cycles for Shijiazhuang station.
