Abstract: Based on the ground observations by the Xinjiang Bureau of Meteorology, the trend，periods and abrupt change of pan evaporation were analyzed in Weigan River Basin with methods of linear analysis, annual anomalies, abrupt t test, wavelet analysis and grey forecasting. The results indicated that as a whole, the annual pan evaporation trend was decreasing in the Weigan River Basin during the given 50 years. The average change was -19.72 mm/10a, which passed the significance test at 0.05 level. The results also showed the annual pan evaporation changes during 1987-2004, which had a high period before 1987, a low period 1987-2003 and a high period after 2004. The annual pan evaporation had presented abrupt changes during 1987-2004. The change type was complex, which included mean value changes and transition changes. There were obvious periods of 8, 17 and 20 years for the annual pan evaporation series during the given 50 years in the Weigan River Basin. At the scale of 8 years, there were 7 high value periods and 6 low value periods. At the scale of 17 years, there were 2 high value periods and 2 low value periods. At the scale of 20 years, there were 2 high value periods and 1 low value periods. The predicted amount of pan evaporation from the established grey dynamic model indicates that the dependability of the established grey dynamic model is very high and the predicted result has nicety. The annual pan evaporation will be increasing in the next three years.

Key words: change trend, grey forecasting, pan evaporation, wavelet analysis, Weigan River Basin