Characteristics and Abrupt Change of Temperature in the Hexi corridor in recent 58 years

Based on data of the average monthly temperature,average monthly maximum and minimum temperature from 1951 to 2008 recorded by the surface weather stations in the Hexi Corridor-Dunhuang,Guazhou,Zhangye,Wuwei and Wuqiaoling,this paper analyzes trends and abrupt changes of climate in the region by means of linear fitting,moving average and Mann-Kendall.The research results show that the average annual temperature,average maximum and minimum temperature in the Hexi Corridor present increasing trends,with the temperature increment-ratio 0.19 ℃/10 a,0.14 ℃/10 a and 0.27 ℃/10 a respectively,and the increment-ratio of average annual minimum temperature is obviously greater than that of other two.Average annual temperature in 1950s' was positive anomalies,while negative anomalies in 1960-1987 and positive anomalies after 1987.The minimum of average annual temperature appeared in 1960s',and at the same time the departure from normal value is-0.3 ℃.On the other hand the positive anomaly of average annual temperature from 2001 to 2008 was 1.1 ℃,thereby the warmest time since 1958.The lowest average annual maximum temperature appeared in 1960s',while the highest appeared after 1990s'.The variation of average annual minimum-temperature slightly differed to that of average annual temperature and that of average annual maximum-temperature: the coldest time appeared in 1960s' with a positive departure from the normal value;and the warmest time appeared in 2001-2008;the average minimum-temperature of the warmest times increased of 1.7 ℃ compared with that of the coldest times.A warmly abrupt change was detected in 1997 by using Mann-Kendall method,which is 4 years later than nationwide abrupt change appeared in 1993,and 10 years later than that in north-west region.The average temperature from 1997 to 2008 was of 1.1 ℃ greater than that from 1951 to 1996.The warmly abrupt change of average annual maximum-temperature appeared in 1996,and average annual maximum-temperature from 1996 to 2008 increased of 0.9 ℃ compared with that from 1951 to 1995.The abruptly warming change of average annual minimum-temperature occurred in 1994,3 years and 2 years,respectively,earlier than that of average annual temperature and average annual maximum-temperature.The annual temperature range shown a decrease trend of 0.13 ℃/10 a,while about 0.6 ℃decreased since 2001,due to comparatively large variation in average annual minimum-temperature.The measurement revealed that annual temperature range decreased in 2002.Seasonally,average temperature increased totally,but the increasing magnitudes were different.The average winter temperature shown a steadily increase trend of 0.345 ℃/10 a,and the warming abrupt change appeared in 1986,which is earlier than other seasons.The steadily increasing ratio of average summer temperature was the smallest,and the obviously warming abrupt change was not detected.From 1951 to 2008,average maximum-temperature in winter increased of 0.27 ℃/10 a,which is the largest increasing magnitude in four seasons,and the warming abrupt change occurred in 1985.The increasing ratio of average summer temperature was 0.13 ℃/10 a-the smallest increasing magnitude in four seasons,and the warming abrupt change occurred in 2004.This illustrates that the climate warming in the Hexi Corridor starts from winter.The daily variation range of spring tended to decrease,with a ratio of 0.18 ℃/10 a from 1951-2008,when the abruptly decreasing change occurred in 1980.The daily variation range of summer and autumn decreased by a comparatively small ratio,which was 0.09 ℃/10 a and 0.05 ℃/10 a respectively,the abruptly decreasing change of summer daily variation range appeared in 2004,while that of autumn kept steady.The decreasing trend of winter daily variation range was also obvious,with a decreasing ratio of 0.13 ℃/10 a from 1951 to 2008,and abruptly decreasing change occurred in 1999.The largest increasing ratio occurred in winter and spring minimum temperature,0.42 ℃/10 a and 0.30 ℃/10 a respectively,demonstrating that the decreasing in daily variation range is due to increasing in night temperature.