Characteristics of variations of pan evaporation and its influencing factors in Dalian,Liaoning province

The characteristics of variations of pan evaporation and its influencing factors from 1951 to 2001 were analyzed in Dalian in terms of methods of a linear tendency estimation,an cumulative anomaly and a complete correlation coefficient.The results show that the annual pan evaporation has an increasing trend.The trend is significant in summer,followed in spring.However,it is not significant in autumn and winter.Summer pan evaporation is the main contributor to annual pan evaporation.Annual and seasonal pan evaporation is positively correlated with the sunshine duration,average surface temperature,diurnal range of average temperature and average wind speed,and negatively correlated with average relative humidity.The decreasing average relative humidity and the increasing average surface temperature are the major reasons for the increasing pan evaporation in Dalian.