Aridity Index in Songnen Grassland, Northeast

Reference evapotranspiration (ET0) plays an irreplaceable role in regional dry/wet 15 conditions under the background of climate change. Based on the FAO Penman-Monteith method 16 and daily climate variables, ET0 was calculated for 22 stations in and around Songnen Grassland, 17 northeast China, during 1960-2014. The temporal and spatial variations of ET0 and precipitation (P) 18 were comprehensively analyzed at different time scales by using the Mann-Kendall test, Sen’s slope 19 estimator, and linear regression coupling with break trend analysis. Sensitivity analysis was used 20 to detect the key climate parameter attributed to ET0 change. Then, the role of ET0 in regional 21 dry/wet conditions was discussed by analyzing the relationship between ET0, P and aridity index 22 (AI). Results shown a higher ET0 in the southwest and a lower in the northeast, but P was opposite 23 to that of ET0. Evidently decreasing trend of ET0 at different time scales was detected in almost the 24 entire region, and the significant trend mainly distributed in the eastern, northeastern and central. 25 For the whole region, sensitivity analysis indicated decreasing trend of ET0 was primarily attributed 26 to relative humidity and maximum air temperature. The positive contribution of increasing 27 temperature rising to ET0 was offset by the effect of significantly decreasing relative humidity, wind 28 speed and sunshine duration. In addition, the value of ET0 shown higher in drought years and lower 29 in wet years. 30