Varition of Evaporation and Its Influence Factors over Hami of Xinjiang in Recent 50 Years

Based on the data of 20 cm caliber evaporating pan and the E-601B evaporator as well as other meteorological observations from 1961 to 2010 at Hami national climate reference station,the climatic feature of evaporation in Hami was analyzed,and the relationships between evaporation and other meteorological elements such as wind speed,temperature,sunshine,precipitation,humidity were discussed.The result indicated that the annual,seasonal and monthly evaporation presented the obvious drop tendency in recent 50 years,and before 1990,evaporation was higher than the mean value but then it reduced and was less than the mean value from 1991 to 2010.It dropped quickly in summer,and next in spring,smallest in winter.There was a significant positive correlation between average wind velocity and evaporation,and average wind velocity was the most direct factor affecting evaporation.There was a significant negative correlation between vapor pressure,relative humidity and the evaporation,they were important factors resulted in the reduction of evaporation.Sunshine hours also positively correlated to evaporation,but its impact was less.The influence of temperature on evaporation was not very clear.