Abstract:

Based on the daily measurement  data of 18 national meteorological stations in Shandong Province, statistical analysis, correlation analysis and Mann-Kendall trend test methods were selected to calculate and analyze the trend of pan evaporation and its associated influencing factors over the past 50 years. The results showed that the pan evaporation in the area declined during the studying period,  the  rate of decending was  about 8.78mm／year and  the decline in summer and spring was particularly significant. Spatially, the evaporation decrement increases gradually from coastal area to the inland. After comparison among the meteorological elements, including net solar radiation, wind speed, temperature and vapor pressure difference, in Shandong Province during the same period, it was inferred that the decline of evaporation is a result of multiple factors, among which the net solar radiation and wind speed are the main factors.

Key words:  pan evaporation, changing trend, influencing factor