Variation characteristics and impact factors of pan evaporation in Pearl River Basin, China

With the data of monthly 20 cm pan evaporation and its impact climatic factors at 65 meteorological stations in Pearl River Basin from 1960 to 2001, spatial-temporal change characteristics of pan evaporation are analyzed by using Mann-Kendall test method, complete correlation methods and geographic information systems. The results showed that there was a significant decreasing trend in the observations on pan evaporation in Pearl River Basin, with an average rate of 2.79 mm/a in the whole basin. In autumn and summer, pan evaporation had no apparent decline trend; but in spring and winter, there existed a significant decreasing trend. The spatial distribution of the change rate showed that the maximum decrease of annual pan evaporation mainly occurs in the south and middle of Pearl River Basin. On the attribution, the paper calculated the complete correlation coefficients of eight climate factors with pan evaporation. And decreases in the sunshine duration, diurnal temperature range and the average wind speed were found to be the main influencing factors leading to the decrease of pan evaporation. These can provide references for study of climate change and hydrologic cycle in Pearl River Basin.