Change in pan evaporation and its driving factors in Jiangxi Province

In order to discuss the influences of the climate changes on the land-surface hydrological processes, in this paper, observation data from 79 weather stations of Jiangxi Province from 1960 to 2005 were analyzed, the attributions of changing annual pan evaporation due to percentage of sunshine duration, wind speed, actual vapor pressure, minimum temperature and maximum temperature were evaluated with Penman equation. It showed that the annual pan evaporation in Poyang Lake Basin as a whole had continuously decreased at a rate of -4.57 mm/a in the past 46 years. The major factors for annual pan evaporation decrease were reduced sunshine hours and weakened wind speed, with their attributions of -2.06 mm/a and -2.58 mm/a, respectively, whereas decrease in atmospheric vapor pressure and the increases in both the minimum and maximum temperatures contributed to the relatively smaller annual pan evaporation increase, with their attributions of 0.12 mm/a, 0.50 mm/a and 0.30 mm/a, respectively. In summary, the relative contributions of the five environmental factors to the observed pan evaporation variations were listed in the order of importance: wind speed (56.46%)> percentage of sunshine duration (45.08%)>minimum temperature (-10.94%)> maximum temperature (-6.57%) >vapor pressure (-2.63%).