Variation and influencing factors of pan evaporation in anhui province in latest 45 years

Annual and seasonal variations analyzed by linear tendency estimate and Mann-Kendall test of 20 cm-pan evaporation of 32 meteorological stations over the Yangtze-Huaihe River in Anhui Province from 1963 to 2007 indicated a significant negative trend(-65.3 mm/10 a,confidence level of 0.01).The jump point of the evaporation happened in 1976,and the obvious variation in 1982.The most remarkable decrease happened in summer.The evaporation had a significant negative trend of 24 stations and a positive trend(confidence level of 0.05) of only 1 station,which shows a spatial declining trend of more in North and less in South.Combining with other research on the impact climate factors of evaporation(7 factors:temperature,sunshine duration,daily temperature rang,wind speed,relative humidity,precipitation and low-cloud),the main result indicated as follows:(1)the annual temperature increased and evaporation decreased,therefore the pan evaporation paradox actually existed in Anhui Province,but the correlation between temperature and evaporation was not significant;(2)the evaporation had significant negative correlation with the sunlight,daily temperature range and wind speed,meanwhile the low-cloud cover,precipitation and relative humidity may also play an important role in an unknown mechanism.