Abstract: Using the meteorological data including daily pan evaporation,mean air temperature,minimum and maximum air temperature,relative humidity,sunshine duration and mean wind speed from 1961 to 2010,the characteristics and impact factors of pan evaporation were analyzed based on the methods of a climate inclination rate,an anomalies and correlation in Alar of Tarim irrigation area.The results show that annual fluctuation of pan evaporation is very obvious,with a "high-low-high-low" inter-decadal variability feature.The amplitude of pan evaporation decreases by 62.4 mm per decade (P<0.01),and has totally reduced about 312.0 mm in Alar of Tarim irrigation area in the past 50 years.The pan evaporation is the largest in summer,and then in spring,autumn,and winter in order from 1961 to 2010 in Alar of Tarim irrigation area.The decrease in pan evaporation is relatively larger in winter and summer (P<0.01),relatively smaller in spring (P<0.05),and very little in autumn (P>0.05).The cumulative decrease amplitudes are 81.5 mm,182.5 mm,28.5 mm,and 198.0 mm in spring,summer,autumn,and winter,respectively.The decrease in the annual cumulative pan evaporation depends strongly on the decreasing mean wind speed and increasing mean relative humidity,but less so on air temperature,precipitation,and sunshine duration.However,the decrease trend of seasonal cumulative pan evaporation is determined by the increasing (decreasing) air temperature,declining sunshine duration,increasing (decreasing) precipitation,decreasing mean wind speed,and increasing mean relative humidity together,although in spring and autumn it is little influenced by air temperature and sunshine duration.

Key words: Alar of Tarim irrigation area, Pan evaporation, Meteorological parameters, Correlation analysis