Analysis of pan evaporation change trend and its influencing factors in Sichuan Basin

Based on the data of daily pan evaporation,air temperature,wind speed,sunshine duration,air pressure,and vapor pressure of the Sichuan Basin,the pan evaporation variation and its causes in the basin from 1980 to 2010 were analyzed. The results show that the pan evaporation in the Sichuan Basin had obvious spatial and temporal variation characteristics. The largest pan evaporation was found in midland Sichuan Basin with hilly areas, followed by that in the western Sichuan Plain,and the smallest pan evaporation was found in the parallel valley area in eastern Sichuan Basin. A significant upward trend was found in the annual pan evaporation. The pan evaporation had a significant increasing trend in the autumn and winter,while no significant trend was found in the spring and summer. The main meteorological factors influencing the pan evaporation included the sunshine duration,the average wind speed,vapor pressure,and air temperature,and the impact of sunshine duration on the pan evaporation increase was 1. 71 times that of the wind speed,and 2. 48 times that of the vapor pressure. However, the air temperature could reduce the pan evaporation,and the pan evaporation reduced by the air temperature was one fourth of that reduced by the sunshine duration on average.