Temporal and Spatial Variations of Extreme High-temperature Event of Summer Over Sichuan and Chongqing Region in Last 50 Years

Based on the daily mean temperature data of summer in 1961-2006 from 145 stations over Sichuan and Chongqing region,we analyzed extreme high-temperature event.As these results show,the high frequency regions of extreme high-temperature event are being east of 103°E,like a band from west to east arcoss central of Sichuan basin up to north of Chongqing.The lowest frequency regions of extreme high-temperature event are in Southwest of Sichuan.According to the anomalous spatial distribution of extreme high-temperature event,Sichuan and Chongqing region can be divided into four regions: Northwest of Sichuan Basin,Southeast of Sichuan Basin,Southwest of Western Sichuan plateau and Southwest of Sichuan.By analyzing long-term changing trend,Northwest of Sichuan Basin shows very obvious growth trend,Southeast of Sichuan Basin shows notable reduction trend,the remaining two regions show weak growth trend.In last 50 years,two main changes in Northwest of Sichuan Basin respectively happened around at 1972 and 1993;one main change in Southeast of Sichuan Basin happened around at 1972.