Abstract: Based on monthly observational data sets of 61 meteorological stations from 1961 to 2010, the pan evaporation trend and abrupt change in the Yellow River basin were analyzed by using Mann-Kendall test method, and then the influence factors were detected and analyzed by using multiple regression method and SVD (Singular Value Decomposition). The results show a significant decreasing trend in annual evaporation in 1961-2010, and the most significant decreasing trend occurs in summer. The abrupt changes of annual, spring and summer evaporation occurred in 1979. In the upper, middle and lower reaches of the Yellow River, the annual evaporation decreased at the rates of 2.38 mm/a, 2.35 mm/a and 8.35 mm/a, respectively with the most significant decreasing trend in the lower reaches. As to the spatial distribution, annual, spring and summer evaporation decreased significantly in the river source region, the west and north parts of Hetao region and the north part of Henan Province, while increased significantly in the east part of Hetao region. By using the method of SVD, it is found that there is a correlation between the spatial change of evaporation and different factors. Based on the multiple regression results, it is concluded that in the region with increasing evaporation, the main influence factor is temperature, whereas in the region with decreasing evaporation, the main influence factor is wind speed.

Key words: evaporation, trend, influence factors, Yellow River basin