The Trend of Temperature Variation and Its Possible Causes in Chongqing

Based on the data of mean temperature,mean minimum temperature,and mean maximum temperature, extreme maximum temperature,and extreme minimum temperature in Chongqing from 1924 to 2007,the characteristics of temperature variations are analyzed.The results show that the decrease in the mean temperature in Chongqing is slight in recent 84 years,and the linear trend of the temperature in Chongqing is different from the trend averaged over China.The asymmetric changes of mean minimum temperature and mean maximum temperature, extreme maximum temperature and extreme minimum temperature are distinct.The decrease in the mean maximum temperature has obvious influence on the mean temperature.The mean minimum temperature in addition to that in spring has a more striking increase.The effect of the minimum temperature increasing on the diurnal temperature range decreasing is more obvious than others.The more southward western Pacific subtropical high in the past summers leads to the increase in rainfall and cloud fraction in summer,as well as the decrease in sunshine time in the eastern part of South-West China and the increase in light fog days.It may be the dominative reason for the persistent decrease in the maximum temperature in summer.The decrease in precipitation days,the increase in cloud cover,and the urban heat island effect are the main causes of the significant increase in mean minimum temperature in winter.