Abstract: Based on the daily data from 60 meteorological stations for the period of 1961-2010, spatial and temporal trends of actual evapotranspiration (E) were analyzed by applying the Advection-Aridity model in the Songhua River basin. The research results show that annual E in the Songhua River basin shows a significant upward trend at a rate of about 4.9 mm per decade. More significant upward trend can be detected in spring and winter. While the summer and autumn E show obvious inter-decadal fluctuation. Annual E has similar spatial distribution pattern to those of spring, summer and autumn, with high values located in the southern part and relatively low values in the west part. In 1961-2010, the annual and seasonal air temperatures, especially the minimum air temperature of the Songhua River basin, have significant upward trends, but the sunshine duration and wind speed have significant downward trends. Correlation analysis results show that, the spatial-temporal distribution of the E is derived from the comprehensive impact of the main meteorological factors. In general, the increase of the average/minimum air temperature can give explanations for the rising of annual and seasonal E, especially in spring and winter. In summer and autumn, the E has no significant trend in 1961-2010, because the main meteorological factors such as daily temperature range, actual vapor pressure, wind speed and precipitation all have no obvious trend.

Key words: actual evapotranspiration, Advection-Aridity model (AA model), the Songhua River basin, impact factors