Abstract: Daily reference evapotranspiration(ET0) in growing season(May to September) during 1961-2008 was calculated by using Penman-Monteith equation recommended by FAO,based on daily meteorological data provided by China Meteorological Administer.Temporal variation of ET0 and key meteorological factors were analyzed.Sensitivity of daily ET0 to key climate factors,such as temperature,sunshine hours,average wind speed and average relative humanity,was analyzed by using the methods of response curves,sensitivity matrixes and sensitivity coefficients.The results showed that temperature increased significantly(P<0.01) during 1961 to 2008,while sunshine hours,average wind speed and average relative humidity decreased significantly(P<0.01) in same time.The average daily ET0 uring growing season did not extended±0.3mm per day at the point of 3.60mm per day,and it was steady in these years and got maximum value in 2001(3.87mm per day) and minimum value in 1990(3.28mm per day).Daily ET0 also increased with temperature,sunshine hours and mean wind speed changed from-20% to 20%,while daily ET0 decreased with average relative humidity changed from-20% to 20%.Average daily sensitivity coefficients of meteorological factors during the growing season varied in region,of which temperature was the most sensitive to ET0,followed by average relative humidity,sunshine hours and mean wind speed.

Key words: Reference evapotranspiration(ET0), Penman-Monteith, Sensitivity analysis, Northeast China