Abstract:Reference evapotranspiration (ET 0 ) plays an important role in regional dry/wet conditions. Based on the Food and Agriculture Organization of the United (FAO) Penman-Monteith method and daily climate variables, ET 0 was calculated for 21 stations in and around the Songnen Grassland, northeast China, during 1960China, during -2014. The temporal and spatial variations of ET 0 and precipitation (P) were analyzed in the annual, seasonal, and growing season (from April to October) time series using the Mann-Kendall test, Sen's slope estimator, and linear regression coupled with a break trend analysis. A sensitivity analysis was used to detect the key climate parameter contributing to ET 0 change. By linear regression analysis on the relationship between ET 0 , P, and the aridity index (AI), the role of ET 0 in determining regional wet/dry conditions was analyzed. Results show a higher ET 0 in the southwest and a lower ET 0 in the northeast, but P was opposite to that of ET 0 . Evident decreasing trends of ET 0 in the annual, seasonal, and growing season time series were detected in almost the entire region by the trend analysis methods. For the entire region, the decreasing trend of ET 0 can be linked to the relative humidity and maximum air temperature. The positive contribution of increasing temperature to ET 0 was offset by the effect of the significantly decreasing relative humidity, wind speed, and sunshine duration at the 0.05 level during 1960-2014. In addition, the value of ET 0 was higher in drought years and lower in wet years.